[RESEND,v2] riscv: Introduce CONFIG_RELOCATABLE

Message ID	20200303054437.650-1-alex@ghiti.fr (mailing list archive)
State	New, archived
Headers	show Return-Path: <SRS0=0URg=4U=lists.infradead.org=linux-riscv-bounces+patchwork-linux-riscv=patchwork.kernel.org@kernel.org> DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0533C20716 sender: alex@ghiti.fr) by relay10.mail.gandi.net (Postfix) with ESMTPSA id 1C633240005; Tue, 3 Mar 2020 05:44:40 +0000 (UTC) From: Alexandre Ghiti <alex@ghiti.fr> To: Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Zong Li <zong.li@sifive.com>, Anup Patel <anup@brainfault.org>, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH RESEND v2] riscv: Introduce CONFIG_RELOCATABLE Date: Tue, 3 Mar 2020 00:44:37 -0500 Message-Id: <20200303054437.650-1-alex@ghiti.fr> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit summary: Content analysis details: (-2.6 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -1.9 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] -0.7 RCVD_IN_DNSWL_LOW RBL: Sender listed at https://www.dnswl.org/, low trust [217.70.178.230 listed in list.dnswl.org] 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record 0.0 SPF_NONE SPF: sender does not publish an SPF Record Precedence: list Cc: Alexandre Ghiti <alex@ghiti.fr> Sender: "linux-riscv" <linux-riscv-bounces@lists.infradead.org> Errors-To: linux-riscv-bounces+patchwork-linux-riscv=patchwork.kernel.org@lists.infradead.org
Series	[RESEND,v2] riscv: Introduce CONFIG_RELOCATABLE \| expand [RESEND,v2] riscv: Introduce CONFIG_RELOCATABLE

Alexandre Ghiti March 3, 2020, 5:44 a.m. UTC

This config allows to compile the kernel as PIE and to relocate it at any
virtual address at runtime: this paves the way to KASLR and to 4-level
page table folding at runtime. Runtime relocation is possible since
relocation metadata are embedded into the kernel.

Note that relocating at runtime introduces an overhead even if the kernel
is loaded at the same address it was linked at and that the compiler
options are those used in arm64 which uses the same RELA relocation format.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org> 
Tested-by: Zong Li <zong.li@sifive.com>
---
Changes in v2:                                                                   
- Make RELOCATABLE depend on MMU as suggested by Anup                            
- Rename kernel_load_addr into kernel_virt_addr as suggested by Anup             
- Use __pa_symbol instead of __pa, as suggested by Zong                          
- Rebased on top of v5.6-rc3                                                     
- Tested with sv48 patchset
- Add Reviewed/Tested-by from Zong and Anup

 arch/riscv/Kconfig              | 12 +++++
 arch/riscv/Makefile             |  5 +-
 arch/riscv/boot/loader.lds.S    |  2 +-
 arch/riscv/include/asm/page.h   |  5 +-
 arch/riscv/kernel/head.S        |  3 +-
 arch/riscv/kernel/vmlinux.lds.S | 10 ++--
 arch/riscv/mm/Makefile          |  4 ++
 arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
 8 files changed, 111 insertions(+), 22 deletions(-)

Palmer Dabbelt March 6, 2020, 5:58 p.m. UTC | #1

On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
> This config allows to compile the kernel as PIE and to relocate it at any
> virtual address at runtime: this paves the way to KASLR and to 4-level
> page table folding at runtime. Runtime relocation is possible since
> relocation metadata are embedded into the kernel.
>
> Note that relocating at runtime introduces an overhead even if the kernel
> is loaded at the same address it was linked at and that the compiler
> options are those used in arm64 which uses the same RELA relocation format.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> Reviewed-by: Zong Li <zong.li@sifive.com>
> Reviewed-by: Anup Patel <anup@brainfault.org>
> Tested-by: Zong Li <zong.li@sifive.com>
> ---
> Changes in v2:
> - Make RELOCATABLE depend on MMU as suggested by Anup
> - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
> - Use __pa_symbol instead of __pa, as suggested by Zong
> - Rebased on top of v5.6-rc3
> - Tested with sv48 patchset
> - Add Reviewed/Tested-by from Zong and Anup
>
>  arch/riscv/Kconfig              | 12 +++++
>  arch/riscv/Makefile             |  5 +-
>  arch/riscv/boot/loader.lds.S    |  2 +-
>  arch/riscv/include/asm/page.h   |  5 +-
>  arch/riscv/kernel/head.S        |  3 +-
>  arch/riscv/kernel/vmlinux.lds.S | 10 ++--
>  arch/riscv/mm/Makefile          |  4 ++
>  arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
>  8 files changed, 111 insertions(+), 22 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 73f029eae0cc..f5f3d474504d 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
>  	default 3 if 64BIT
>  	default 2
>
> +config RELOCATABLE
> +	bool
> +	depends on MMU
> +	help
> +          This builds a kernel as a Position Independent Executable (PIE),
> +          which retains all relocation metadata required to relocate the
> +          kernel binary at runtime to a different virtual address than the
> +          address it was linked at.
> +          Since RISCV uses the RELA relocation format, this requires a
> +          relocation pass at runtime even if the kernel is loaded at the
> +          same address it was linked at.
> +
>  source "arch/riscv/Kconfig.socs"
>
>  menu "Platform type"
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index b9009a2fbaf5..5a115cf6a9c1 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -9,7 +9,10 @@
>  #
>
>  OBJCOPYFLAGS    := -O binary
> -LDFLAGS_vmlinux :=
> +ifeq ($(CONFIG_RELOCATABLE),y)
> +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
> +KBUILD_CFLAGS += -fPIE
> +endif
>  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>  	LDFLAGS_vmlinux := --no-relax
>  endif
> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
> index 47a5003c2e28..a9ed218171aa 100644
> --- a/arch/riscv/boot/loader.lds.S
> +++ b/arch/riscv/boot/loader.lds.S
> @@ -7,7 +7,7 @@ ENTRY(_start)
>
>  SECTIONS
>  {
> -	. = PAGE_OFFSET;
> +	. = CONFIG_PAGE_OFFSET;
>
>  	.payload : {
>  		*(.payload)
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 8ca1930caa44..af5810f9aebd 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -31,9 +31,9 @@
>   * When not using MMU this corresponds to the first free page in
>   * physical memory (aligned on a page boundary).
>   */
> -#define PAGE_OFFSET		_AC(CONFIG_PAGE_OFFSET, UL)
> +#define PAGE_OFFSET		kernel_virt_addr

I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
systems.  As it currently stands this is imposing a performance hit even when 

> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
> +#define KERN_VIRT_SIZE		(-_AC(CONFIG_PAGE_OFFSET, UL))

This seems like it would cause issues if the kernel is relocated to high enough
addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.

>  #ifndef __ASSEMBLY__
>
> @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
>  #define ARCH_PFN_OFFSET		(PAGE_OFFSET >> PAGE_SHIFT)
>  #endif /* CONFIG_MMU */
>
> +extern unsigned long kernel_virt_addr;
>  extern unsigned long max_low_pfn;
>  extern unsigned long min_low_pfn;
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 271860fc2c3f..d792912c2da3 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -131,7 +131,8 @@ clear_bss_done:
>  #ifdef CONFIG_MMU
>  relocate:
>  	/* Relocate return address */
> -	li a1, PAGE_OFFSET
> +	la a1, kernel_virt_addr
> +	REG_L a1, 0(a1)
>  	la a2, _start
>  	sub a1, a1, a2
>  	add ra, ra, a1
> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index 1e0193ded420..5bf69e9b91e6 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -4,7 +4,7 @@
>   * Copyright (C) 2017 SiFive
>   */
>
> -#define LOAD_OFFSET PAGE_OFFSET
> +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
>  #include <asm/vmlinux.lds.h>
>  #include <asm/page.h>
>  #include <asm/cache.h>
> @@ -71,9 +71,11 @@ SECTIONS
>
>  	EXCEPTION_TABLE(0x10)
>
> -	.rel.dyn : {
> -		*(.rel.dyn*)
> -	}
> +        .rela.dyn : ALIGN(8) {
> +		__rela_dyn_start = .;
> +                *(.rela .rela*)
> +		__rela_dyn_end = .;
> +        }

It looks like the indentation is screwed up here: I see a mix of tabs/spaces
that doesn't match the rest of the file.

>
>  	_end = .;
>
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index 50b7af58c566..27593d362248 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -1,6 +1,10 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>
>  CFLAGS_init.o := -mcmodel=medany
> +ifdef CONFIG_RELOCATABLE
> +CFLAGS_init.o += -fno-pie
> +endif
> +
>  ifdef CONFIG_FTRACE
>  CFLAGS_REMOVE_init.o = -pg
>  endif
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 965a8cf4829c..428aee2669aa 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -12,6 +12,9 @@
>  #include <linux/sizes.h>
>  #include <linux/of_fdt.h>
>  #include <linux/libfdt.h>
> +#ifdef CONFIG_RELOCATABLE
> +#include <linux/elf.h>
> +#endif
>
>  #include <asm/fixmap.h>
>  #include <asm/tlbflush.h>
> @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
>  extern char _start[];
>  void *dtb_early_va;
>
> +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> +EXPORT_SYMBOL(kernel_virt_addr);
> +
>  static void __init zone_sizes_init(void)
>  {
>  	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
> @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
>  		phys_addr_t end = reg->base + reg->size;
>
>  		if (reg->base <= vmlinux_end && vmlinux_end <= end) {
> -			mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
> +			mem_size = min(reg->size,
> +				       (phys_addr_t)-kernel_virt_addr);

PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these --
they account for a significant fraction of the diff.

>  			/*
>  			 * Remove memblock from the end of usable area to the
> @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>  	if (mmu_enabled)
>  		return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>
> -	pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> +	pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
>  	BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>  	return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>  }
> @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>  #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
>  #endif
>
> +#ifdef CONFIG_RELOCATABLE
> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
> +
> +#ifdef CONFIG_64BIT
> +#define Elf_Rela Elf64_Rela
> +#define Elf_Addr Elf64_Addr
> +#else
> +#define Elf_Rela Elf32_Rela
> +#define Elf_Addr Elf32_Addr
> +#endif
> +
> +void __init relocate_kernel(uintptr_t load_pa)
> +{
> +	Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
> +	uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> +	/*
> +	 * This holds the offset between the linked virtual address and the
> +	 * relocated virtual address.
> +	 */
> +	uintptr_t reloc_offset = kernel_virt_addr - link_addr;
> +	/*
> +	 * This holds the offset between linked virtual address and physical
> +	 * address whereas va_pa_offset holds the offset between relocated
> +	 * virtual address and physical address.
> +	 */
> +	uintptr_t va_link_pa_offset = link_addr - load_pa;
> +
> +	for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
> +		Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
> +		Elf_Addr relocated_addr = rela->r_addend;
> +
> +		if (rela->r_info != R_RISCV_RELATIVE)
> +			continue;

This should at least provide a warning when it encounters an unresolvable
relocation.  Is it currently stands this just ignores all other runtime
relocations, and while I can buy the argument there shouldn't be any (though
I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently
skip them.

> +
> +		/*
> +		 * Make sure to not relocate vdso symbols like rt_sigreturn
> +		 * which are linked from the address 0 in vmlinux since
> +		 * vdso symbol addresses are actually used as an offset from
> +		 * mm->context.vdso in VDSO_OFFSET macro.
> +		 */
> +		if (relocated_addr >= link_addr)
> +			relocated_addr += reloc_offset;
> +
> +		*(Elf_Addr *)addr = relocated_addr;
> +	}
> +}
> +#endif
> +
>  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  {
>  	uintptr_t va, end_va;
> @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>  	uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>
> -	va_pa_offset = PAGE_OFFSET - load_pa;
> +	va_pa_offset = kernel_virt_addr - load_pa;
>  	pfn_base = PFN_DOWN(load_pa);
>
> +#ifdef CONFIG_RELOCATABLE
> +	/*
> +	 * Early page table uses only one PGDIR, which makes it possible
> +	 * to map 1GB aligned on 1GB: if the relocation offset makes the kernel
> +	 * cross over a 1G boundary, raise a bug since a part of the kernel
> +	 * would not get mapped.
> +	 */
> +	BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
> +	relocate_kernel(load_pa);
> +#endif
> +
>  	/*
>  	 * Enforce boot alignment requirements of RV32 and
>  	 * RV64 by only allowing PMD or PGD mappings.
> @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	BUG_ON(map_size == PAGE_SIZE);
>
>  	/* Sanity check alignment and size */
> -	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
> +	BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
>  	BUG_ON((load_pa % map_size) != 0);
>  	BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
>
> @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	create_pmd_mapping(fixmap_pmd, FIXADDR_START,
>  			   (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
>  	/* Setup trampoline PGD and PMD */
> -	create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> +	create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>  			   (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
> -	create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
> +	create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>  			   load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>  #else
>  	/* Setup trampoline PGD */
> -	create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> +	create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>  			   load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
>  #endif
>
> @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>  	 * us to reach paging_init(). We map all memory banks later
>  	 * in setup_vm_final() below.
>  	 */
> -	end_va = PAGE_OFFSET + load_sz;
> -	for (va = PAGE_OFFSET; va < end_va; va += map_size)
> +	end_va = kernel_virt_addr + load_sz;
> +	for (va = kernel_virt_addr; va < end_va; va += map_size)
>  		create_pgd_mapping(early_pg_dir, va,
> -				   load_pa + (va - PAGE_OFFSET),
> +				   load_pa + (va - kernel_virt_addr),
>  				   map_size, PAGE_KERNEL_EXEC);
>
>  	/* Create fixed mapping for early FDT parsing */
> @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
>  			break;
>  		if (memblock_is_nomap(reg))
>  			continue;
> -		if (start <= __pa(PAGE_OFFSET) &&
> -		    __pa(PAGE_OFFSET) < end)
> -			start = __pa(PAGE_OFFSET);
> +		if (start <= __pa_symbol(kernel_virt_addr) &&
> +		    __pa(kernel_virt_addr) < end)
> +			start = __pa_symbol(kernel_virt_addr);
>
>  		map_size = best_map_size(start, end - start);
>  		for (pa = start; pa < end; pa += map_size) {

Alexandre Ghiti March 7, 2020, 10:16 a.m. UTC | #2

Hi Palmer,

On 3/6/20 12:58 PM, Palmer Dabbelt wrote:
> On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
>> This config allows to compile the kernel as PIE and to relocate it at any
>> virtual address at runtime: this paves the way to KASLR and to 4-level
>> page table folding at runtime. Runtime relocation is possible since
>> relocation metadata are embedded into the kernel.
>>
>> Note that relocating at runtime introduces an overhead even if the kernel
>> is loaded at the same address it was linked at and that the compiler
>> options are those used in arm64 which uses the same RELA relocation 
>> format.
>>
>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>> Reviewed-by: Zong Li <zong.li@sifive.com>
>> Reviewed-by: Anup Patel <anup@brainfault.org>
>> Tested-by: Zong Li <zong.li@sifive.com>
>> ---
>> Changes in v2:
>> - Make RELOCATABLE depend on MMU as suggested by Anup
>> - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
>> - Use __pa_symbol instead of __pa, as suggested by Zong
>> - Rebased on top of v5.6-rc3
>> - Tested with sv48 patchset
>> - Add Reviewed/Tested-by from Zong and Anup
>>
>>  arch/riscv/Kconfig              | 12 +++++
>>  arch/riscv/Makefile             |  5 +-
>>  arch/riscv/boot/loader.lds.S    |  2 +-
>>  arch/riscv/include/asm/page.h   |  5 +-
>>  arch/riscv/kernel/head.S        |  3 +-
>>  arch/riscv/kernel/vmlinux.lds.S | 10 ++--
>>  arch/riscv/mm/Makefile          |  4 ++
>>  arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
>>  8 files changed, 111 insertions(+), 22 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 73f029eae0cc..f5f3d474504d 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
>>      default 3 if 64BIT
>>      default 2
>>
>> +config RELOCATABLE
>> +    bool
>> +    depends on MMU
>> +    help
>> +          This builds a kernel as a Position Independent Executable 
>> (PIE),
>> +          which retains all relocation metadata required to relocate the
>> +          kernel binary at runtime to a different virtual address 
>> than the
>> +          address it was linked at.
>> +          Since RISCV uses the RELA relocation format, this requires a
>> +          relocation pass at runtime even if the kernel is loaded at the
>> +          same address it was linked at.
>> +
>>  source "arch/riscv/Kconfig.socs"
>>
>>  menu "Platform type"
>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>> index b9009a2fbaf5..5a115cf6a9c1 100644
>> --- a/arch/riscv/Makefile
>> +++ b/arch/riscv/Makefile
>> @@ -9,7 +9,10 @@
>>  #
>>
>>  OBJCOPYFLAGS    := -O binary
>> -LDFLAGS_vmlinux :=
>> +ifeq ($(CONFIG_RELOCATABLE),y)
>> +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
>> +KBUILD_CFLAGS += -fPIE
>> +endif
>>  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>>      LDFLAGS_vmlinux := --no-relax
>>  endif
>> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
>> index 47a5003c2e28..a9ed218171aa 100644
>> --- a/arch/riscv/boot/loader.lds.S
>> +++ b/arch/riscv/boot/loader.lds.S
>> @@ -7,7 +7,7 @@ ENTRY(_start)
>>
>>  SECTIONS
>>  {
>> -    . = PAGE_OFFSET;
>> +    . = CONFIG_PAGE_OFFSET;
>>
>>      .payload : {
>>          *(.payload)
>> diff --git a/arch/riscv/include/asm/page.h 
>> b/arch/riscv/include/asm/page.h
>> index 8ca1930caa44..af5810f9aebd 100644
>> --- a/arch/riscv/include/asm/page.h
>> +++ b/arch/riscv/include/asm/page.h
>> @@ -31,9 +31,9 @@
>>   * When not using MMU this corresponds to the first free page in
>>   * physical memory (aligned on a page boundary).
>>   */
>> -#define PAGE_OFFSET        _AC(CONFIG_PAGE_OFFSET, UL)
>> +#define PAGE_OFFSET        kernel_virt_addr
> 
> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
> systems.  As it currently stands this is imposing a performance hit even 
> when

Ok I can do that, thanks.

>> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
>> +#define KERN_VIRT_SIZE        (-_AC(CONFIG_PAGE_OFFSET, UL))
> 
> This seems like it would cause issues if the kernel is relocated to high 
> enough
> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.

KERN_VIRT_SIZE is only used to define the size of VMALLOC zone and 
VMALLOC zone must aligned on 2MB (size of PMD page): so I simply used 
CONFIG_PAGE_OFFSET that guarantees that (since aligned on 1GB).

But I should define KERN_VIRT_SIZE by using kernel_virt_addr and make 
sure that VMALLOC zone is aligned on 2MB.

Ok I'll fix that in v3, thanks.

> 
>>  #ifndef __ASSEMBLY__
>>
>> @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
>>  #define ARCH_PFN_OFFSET        (PAGE_OFFSET >> PAGE_SHIFT)
>>  #endif /* CONFIG_MMU */
>>
>> +extern unsigned long kernel_virt_addr;
>>  extern unsigned long max_low_pfn;
>>  extern unsigned long min_low_pfn;
>>
>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>> index 271860fc2c3f..d792912c2da3 100644
>> --- a/arch/riscv/kernel/head.S
>> +++ b/arch/riscv/kernel/head.S
>> @@ -131,7 +131,8 @@ clear_bss_done:
>>  #ifdef CONFIG_MMU
>>  relocate:
>>      /* Relocate return address */
>> -    li a1, PAGE_OFFSET
>> +    la a1, kernel_virt_addr
>> +    REG_L a1, 0(a1)
>>      la a2, _start
>>      sub a1, a1, a2
>>      add ra, ra, a1
>> diff --git a/arch/riscv/kernel/vmlinux.lds.S 
>> b/arch/riscv/kernel/vmlinux.lds.S
>> index 1e0193ded420..5bf69e9b91e6 100644
>> --- a/arch/riscv/kernel/vmlinux.lds.S
>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>> @@ -4,7 +4,7 @@
>>   * Copyright (C) 2017 SiFive
>>   */
>>
>> -#define LOAD_OFFSET PAGE_OFFSET
>> +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
>>  #include <asm/vmlinux.lds.h>
>>  #include <asm/page.h>
>>  #include <asm/cache.h>
>> @@ -71,9 +71,11 @@ SECTIONS
>>
>>      EXCEPTION_TABLE(0x10)
>>
>> -    .rel.dyn : {
>> -        *(.rel.dyn*)
>> -    }
>> +        .rela.dyn : ALIGN(8) {
>> +        __rela_dyn_start = .;
>> +                *(.rela .rela*)
>> +        __rela_dyn_end = .;
>> +        }
> 
> It looks like the indentation is screwed up here: I see a mix of 
> tabs/spaces
> that doesn't match the rest of the file.
> 

Thanks, I'll fix it.

>>
>>      _end = .;
>>
>> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
>> index 50b7af58c566..27593d362248 100644
>> --- a/arch/riscv/mm/Makefile
>> +++ b/arch/riscv/mm/Makefile
>> @@ -1,6 +1,10 @@
>>  # SPDX-License-Identifier: GPL-2.0-only
>>
>>  CFLAGS_init.o := -mcmodel=medany
>> +ifdef CONFIG_RELOCATABLE
>> +CFLAGS_init.o += -fno-pie
>> +endif
>> +
>>  ifdef CONFIG_FTRACE
>>  CFLAGS_REMOVE_init.o = -pg
>>  endif
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index 965a8cf4829c..428aee2669aa 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -12,6 +12,9 @@
>>  #include <linux/sizes.h>
>>  #include <linux/of_fdt.h>
>>  #include <linux/libfdt.h>
>> +#ifdef CONFIG_RELOCATABLE
>> +#include <linux/elf.h>
>> +#endif
>>
>>  #include <asm/fixmap.h>
>>  #include <asm/tlbflush.h>
>> @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
>>  extern char _start[];
>>  void *dtb_early_va;
>>
>> +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>> +EXPORT_SYMBOL(kernel_virt_addr);
>> +
>>  static void __init zone_sizes_init(void)
>>  {
>>      unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
>> @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
>>          phys_addr_t end = reg->base + reg->size;
>>
>>          if (reg->base <= vmlinux_end && vmlinux_end <= end) {
>> -            mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
>> +            mem_size = min(reg->size,
>> +                       (phys_addr_t)-kernel_virt_addr);
> 
> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change 
> these --
> they account for a significant fraction of the diff.

You are totally right, those are leftovers from a previous version. 
Thanks for catching that, that greatly simplifies this patch.

> 
>>              /*
>>               * Remove memblock from the end of usable area to the
>> @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>>      if (mmu_enabled)
>>          return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>
>> -    pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>> +    pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
>>      BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>>      return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>>  }
>> @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t 
>> base, phys_addr_t size)
>>  #error "setup_vm() is called from head.S before relocate so it should 
>> not use absolute addressing."
>>  #endif
>>
>> +#ifdef CONFIG_RELOCATABLE
>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
>> +
>> +#ifdef CONFIG_64BIT
>> +#define Elf_Rela Elf64_Rela
>> +#define Elf_Addr Elf64_Addr
>> +#else
>> +#define Elf_Rela Elf32_Rela
>> +#define Elf_Addr Elf32_Addr
>> +#endif
>> +
>> +void __init relocate_kernel(uintptr_t load_pa)
>> +{
>> +    Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
>> +    uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>> +    /*
>> +     * This holds the offset between the linked virtual address and the
>> +     * relocated virtual address.
>> +     */
>> +    uintptr_t reloc_offset = kernel_virt_addr - link_addr;
>> +    /*
>> +     * This holds the offset between linked virtual address and physical
>> +     * address whereas va_pa_offset holds the offset between relocated
>> +     * virtual address and physical address.
>> +     */
>> +    uintptr_t va_link_pa_offset = link_addr - load_pa;
>> +
>> +    for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
>> +        Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
>> +        Elf_Addr relocated_addr = rela->r_addend;
>> +
>> +        if (rela->r_info != R_RISCV_RELATIVE)
>> +            continue;
> 
> This should at least provide a warning when it encounters an unresolvable
> relocation.  Is it currently stands this just ignores all other runtime
> relocations, and while I can buy the argument there shouldn't be any 
> (though
> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just 
> silently
> skip them.
> 

It's hard to warn that early in the boot process: what about we do like 
powerpc and warns at compile time ? In addition, it would be better that 
way since we can eliminate false-positive like in 43e76cd368fb (because 
the only R_RISCV_64 relocations are indeed false-positive).

>> +
>> +        /*
>> +         * Make sure to not relocate vdso symbols like rt_sigreturn
>> +         * which are linked from the address 0 in vmlinux since
>> +         * vdso symbol addresses are actually used as an offset from
>> +         * mm->context.vdso in VDSO_OFFSET macro.
>> +         */
>> +        if (relocated_addr >= link_addr)
>> +            relocated_addr += reloc_offset;
>> +
>> +        *(Elf_Addr *)addr = relocated_addr;
>> +    }
>> +}
>> +#endif
>> +
>>  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>  {
>>      uintptr_t va, end_va;
>> @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>      uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>>      uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>>
>> -    va_pa_offset = PAGE_OFFSET - load_pa;
>> +    va_pa_offset = kernel_virt_addr - load_pa;
>>      pfn_base = PFN_DOWN(load_pa);
>>
>> +#ifdef CONFIG_RELOCATABLE
>> +    /*
>> +     * Early page table uses only one PGDIR, which makes it possible
>> +     * to map 1GB aligned on 1GB: if the relocation offset makes the 
>> kernel
>> +     * cross over a 1G boundary, raise a bug since a part of the kernel
>> +     * would not get mapped.
>> +     */
>> +    BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
>> +    relocate_kernel(load_pa);
>> +#endif
>> +
>>      /*
>>       * Enforce boot alignment requirements of RV32 and
>>       * RV64 by only allowing PMD or PGD mappings.
>> @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>      BUG_ON(map_size == PAGE_SIZE);
>>
>>      /* Sanity check alignment and size */
>> -    BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
>> +    BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
>>      BUG_ON((load_pa % map_size) != 0);
>>      BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
>>
>> @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>      create_pmd_mapping(fixmap_pmd, FIXADDR_START,
>>                 (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
>>      /* Setup trampoline PGD and PMD */
>> -    create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>> +    create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>                 (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
>> -    create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
>> +    create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>>                 load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>>  #else
>>      /* Setup trampoline PGD */
>> -    create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>> +    create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>                 load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
>>  #endif
>>
>> @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>       * us to reach paging_init(). We map all memory banks later
>>       * in setup_vm_final() below.
>>       */
>> -    end_va = PAGE_OFFSET + load_sz;
>> -    for (va = PAGE_OFFSET; va < end_va; va += map_size)
>> +    end_va = kernel_virt_addr + load_sz;
>> +    for (va = kernel_virt_addr; va < end_va; va += map_size)
>>          create_pgd_mapping(early_pg_dir, va,
>> -                   load_pa + (va - PAGE_OFFSET),
>> +                   load_pa + (va - kernel_virt_addr),
>>                     map_size, PAGE_KERNEL_EXEC);
>>
>>      /* Create fixed mapping for early FDT parsing */
>> @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
>>              break;
>>          if (memblock_is_nomap(reg))
>>              continue;
>> -        if (start <= __pa(PAGE_OFFSET) &&
>> -            __pa(PAGE_OFFSET) < end)
>> -            start = __pa(PAGE_OFFSET);
>> +        if (start <= __pa_symbol(kernel_virt_addr) &&
>> +            __pa(kernel_virt_addr) < end)
>> +            start = __pa_symbol(kernel_virt_addr);
>>
>>          map_size = best_map_size(start, end - start);
>>          for (pa = start; pa < end; pa += map_size) {

Thanks Palmer,

Alex

Zong Li March 12, 2020, 5:57 a.m. UTC | #3

On Sat, Mar 7, 2020 at 1:58 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
> > This config allows to compile the kernel as PIE and to relocate it at any
> > virtual address at runtime: this paves the way to KASLR and to 4-level
> > page table folding at runtime. Runtime relocation is possible since
> > relocation metadata are embedded into the kernel.
> >
> > Note that relocating at runtime introduces an overhead even if the kernel
> > is loaded at the same address it was linked at and that the compiler
> > options are those used in arm64 which uses the same RELA relocation format.
> >
> > Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> > Reviewed-by: Zong Li <zong.li@sifive.com>
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > Tested-by: Zong Li <zong.li@sifive.com>
> > ---
> > Changes in v2:
> > - Make RELOCATABLE depend on MMU as suggested by Anup
> > - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
> > - Use __pa_symbol instead of __pa, as suggested by Zong
> > - Rebased on top of v5.6-rc3
> > - Tested with sv48 patchset
> > - Add Reviewed/Tested-by from Zong and Anup
> >
> >  arch/riscv/Kconfig              | 12 +++++
> >  arch/riscv/Makefile             |  5 +-
> >  arch/riscv/boot/loader.lds.S    |  2 +-
> >  arch/riscv/include/asm/page.h   |  5 +-
> >  arch/riscv/kernel/head.S        |  3 +-
> >  arch/riscv/kernel/vmlinux.lds.S | 10 ++--
> >  arch/riscv/mm/Makefile          |  4 ++
> >  arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
> >  8 files changed, 111 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 73f029eae0cc..f5f3d474504d 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
> >       default 3 if 64BIT
> >       default 2
> >
> > +config RELOCATABLE
> > +     bool
> > +     depends on MMU
> > +     help
> > +          This builds a kernel as a Position Independent Executable (PIE),
> > +          which retains all relocation metadata required to relocate the
> > +          kernel binary at runtime to a different virtual address than the
> > +          address it was linked at.
> > +          Since RISCV uses the RELA relocation format, this requires a
> > +          relocation pass at runtime even if the kernel is loaded at the
> > +          same address it was linked at.
> > +
> >  source "arch/riscv/Kconfig.socs"
> >
> >  menu "Platform type"
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index b9009a2fbaf5..5a115cf6a9c1 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -9,7 +9,10 @@
> >  #
> >
> >  OBJCOPYFLAGS    := -O binary
> > -LDFLAGS_vmlinux :=
> > +ifeq ($(CONFIG_RELOCATABLE),y)
> > +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
> > +KBUILD_CFLAGS += -fPIE
> > +endif
> >  ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> >       LDFLAGS_vmlinux := --no-relax
> >  endif
> > diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
> > index 47a5003c2e28..a9ed218171aa 100644
> > --- a/arch/riscv/boot/loader.lds.S
> > +++ b/arch/riscv/boot/loader.lds.S
> > @@ -7,7 +7,7 @@ ENTRY(_start)
> >
> >  SECTIONS
> >  {
> > -     . = PAGE_OFFSET;
> > +     . = CONFIG_PAGE_OFFSET;
> >
> >       .payload : {
> >               *(.payload)
> > diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> > index 8ca1930caa44..af5810f9aebd 100644
> > --- a/arch/riscv/include/asm/page.h
> > +++ b/arch/riscv/include/asm/page.h
> > @@ -31,9 +31,9 @@
> >   * When not using MMU this corresponds to the first free page in
> >   * physical memory (aligned on a page boundary).
> >   */
> > -#define PAGE_OFFSET          _AC(CONFIG_PAGE_OFFSET, UL)
> > +#define PAGE_OFFSET          kernel_virt_addr
>
> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
> systems.  As it currently stands this is imposing a performance hit even when
>

I had almost done the KASLR implementation on top of this patch.
Actually, PAGE_OFFSET change is unnecessary in KASLR , because we
would move kernel image to a random physical address as well, so the
$pc will go to the relevant random virtual address. We need
kernel_virt_addr to record the new destination, but keep PAGE_OFFSET
to be CONFIG_PAGE_OFFSET is enough.

> > -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
> > +#define KERN_VIRT_SIZE               (-_AC(CONFIG_PAGE_OFFSET, UL))
>
> This seems like it would cause issues if the kernel is relocated to high enough
> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.
>

Based on the same reason, keep KERN_VIRT_SIZE to be -PAGE_OFFSET is good.

> >  #ifndef __ASSEMBLY__
> >
> > @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
> >  #define ARCH_PFN_OFFSET              (PAGE_OFFSET >> PAGE_SHIFT)
> >  #endif /* CONFIG_MMU */
> >
> > +extern unsigned long kernel_virt_addr;
> >  extern unsigned long max_low_pfn;
> >  extern unsigned long min_low_pfn;
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 271860fc2c3f..d792912c2da3 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -131,7 +131,8 @@ clear_bss_done:
> >  #ifdef CONFIG_MMU
> >  relocate:
> >       /* Relocate return address */
> > -     li a1, PAGE_OFFSET
> > +     la a1, kernel_virt_addr
> > +     REG_L a1, 0(a1)
> >       la a2, _start
> >       sub a1, a1, a2
> >       add ra, ra, a1
> > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > index 1e0193ded420..5bf69e9b91e6 100644
> > --- a/arch/riscv/kernel/vmlinux.lds.S
> > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > @@ -4,7 +4,7 @@
> >   * Copyright (C) 2017 SiFive
> >   */
> >
> > -#define LOAD_OFFSET PAGE_OFFSET
> > +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
> >  #include <asm/vmlinux.lds.h>
> >  #include <asm/page.h>
> >  #include <asm/cache.h>
> > @@ -71,9 +71,11 @@ SECTIONS
> >
> >       EXCEPTION_TABLE(0x10)
> >
> > -     .rel.dyn : {
> > -             *(.rel.dyn*)
> > -     }
> > +        .rela.dyn : ALIGN(8) {
> > +             __rela_dyn_start = .;
> > +                *(.rela .rela*)
> > +             __rela_dyn_end = .;
> > +        }
>
> It looks like the indentation is screwed up here: I see a mix of tabs/spaces
> that doesn't match the rest of the file.
>
> >
> >       _end = .;
> >
> > diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> > index 50b7af58c566..27593d362248 100644
> > --- a/arch/riscv/mm/Makefile
> > +++ b/arch/riscv/mm/Makefile
> > @@ -1,6 +1,10 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >
> >  CFLAGS_init.o := -mcmodel=medany
> > +ifdef CONFIG_RELOCATABLE
> > +CFLAGS_init.o += -fno-pie
> > +endif
> > +
> >  ifdef CONFIG_FTRACE
> >  CFLAGS_REMOVE_init.o = -pg
> >  endif
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 965a8cf4829c..428aee2669aa 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -12,6 +12,9 @@
> >  #include <linux/sizes.h>
> >  #include <linux/of_fdt.h>
> >  #include <linux/libfdt.h>
> > +#ifdef CONFIG_RELOCATABLE
> > +#include <linux/elf.h>
> > +#endif
> >
> >  #include <asm/fixmap.h>
> >  #include <asm/tlbflush.h>
> > @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
> >  extern char _start[];
> >  void *dtb_early_va;
> >
> > +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> > +EXPORT_SYMBOL(kernel_virt_addr);
> > +
> >  static void __init zone_sizes_init(void)
> >  {
> >       unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
> > @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
> >               phys_addr_t end = reg->base + reg->size;
> >
> >               if (reg->base <= vmlinux_end && vmlinux_end <= end) {
> > -                     mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
> > +                     mem_size = min(reg->size,
> > +                                    (phys_addr_t)-kernel_virt_addr);
>
> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these --
> they account for a significant fraction of the diff.
>

kernel_virt_addr would be assigned to a random destination by KASLR,
but here still should be PAGE_OFFSET rather than kernel_virt_addr as
mentioned above.

> >                       /*
> >                        * Remove memblock from the end of usable area to the
> > @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
> >       if (mmu_enabled)
> >               return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> >
> > -     pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> > +     pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;

Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.

> >       BUG_ON(pmd_num >= NUM_EARLY_PMDS);
> >       return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
> >  }
> > @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> >  #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
> >  #endif
> >
> > +#ifdef CONFIG_RELOCATABLE
> > +extern unsigned long __rela_dyn_start, __rela_dyn_end;
> > +
> > +#ifdef CONFIG_64BIT
> > +#define Elf_Rela Elf64_Rela
> > +#define Elf_Addr Elf64_Addr
> > +#else
> > +#define Elf_Rela Elf32_Rela
> > +#define Elf_Addr Elf32_Addr
> > +#endif
> > +
> > +void __init relocate_kernel(uintptr_t load_pa)
> > +{
> > +     Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
> > +     uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> > +     /*
> > +      * This holds the offset between the linked virtual address and the
> > +      * relocated virtual address.
> > +      */
> > +     uintptr_t reloc_offset = kernel_virt_addr - link_addr;
> > +     /*
> > +      * This holds the offset between linked virtual address and physical
> > +      * address whereas va_pa_offset holds the offset between relocated
> > +      * virtual address and physical address.
> > +      */
> > +     uintptr_t va_link_pa_offset = link_addr - load_pa;
> > +
> > +     for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
> > +             Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
> > +             Elf_Addr relocated_addr = rela->r_addend;
> > +
> > +             if (rela->r_info != R_RISCV_RELATIVE)
> > +                     continue;
>
> This should at least provide a warning when it encounters an unresolvable
> relocation.  Is it currently stands this just ignores all other runtime
> relocations, and while I can buy the argument there shouldn't be any (though
> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently
> skip them.
>
> > +
> > +             /*
> > +              * Make sure to not relocate vdso symbols like rt_sigreturn
> > +              * which are linked from the address 0 in vmlinux since
> > +              * vdso symbol addresses are actually used as an offset from
> > +              * mm->context.vdso in VDSO_OFFSET macro.
> > +              */
> > +             if (relocated_addr >= link_addr)
> > +                     relocated_addr += reloc_offset;
> > +
> > +             *(Elf_Addr *)addr = relocated_addr;
> > +     }
> > +}
> > +#endif
> > +
> >  asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >  {
> >       uintptr_t va, end_va;
> > @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >       uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
> >       uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> >
> > -     va_pa_offset = PAGE_OFFSET - load_pa;
> > +     va_pa_offset = kernel_virt_addr - load_pa;
> >       pfn_base = PFN_DOWN(load_pa);
> >
> > +#ifdef CONFIG_RELOCATABLE
> > +     /*
> > +      * Early page table uses only one PGDIR, which makes it possible
> > +      * to map 1GB aligned on 1GB: if the relocation offset makes the kernel
> > +      * cross over a 1G boundary, raise a bug since a part of the kernel
> > +      * would not get mapped.
> > +      */
> > +     BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
> > +     relocate_kernel(load_pa);
> > +#endif
> > +
> >       /*
> >        * Enforce boot alignment requirements of RV32 and
> >        * RV64 by only allowing PMD or PGD mappings.
> > @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >       BUG_ON(map_size == PAGE_SIZE);
> >
> >       /* Sanity check alignment and size */
> > -     BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
> > +     BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
> >       BUG_ON((load_pa % map_size) != 0);
> >       BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
> >
> > @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >       create_pmd_mapping(fixmap_pmd, FIXADDR_START,
> >                          (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
> >       /* Setup trampoline PGD and PMD */
> > -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> > +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
> >                          (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
> > -     create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
> > +     create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
> >                          load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
> >  #else
> >       /* Setup trampoline PGD */
> > -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> > +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
> >                          load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
> >  #endif
> >
> > @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >        * us to reach paging_init(). We map all memory banks later
> >        * in setup_vm_final() below.
> >        */
> > -     end_va = PAGE_OFFSET + load_sz;
> > -     for (va = PAGE_OFFSET; va < end_va; va += map_size)
> > +     end_va = kernel_virt_addr + load_sz;
> > +     for (va = kernel_virt_addr; va < end_va; va += map_size)
> >               create_pgd_mapping(early_pg_dir, va,
> > -                                load_pa + (va - PAGE_OFFSET),
> > +                                load_pa + (va - kernel_virt_addr),
> >                                  map_size, PAGE_KERNEL_EXEC);
> >
> >       /* Create fixed mapping for early FDT parsing */
> > @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
> >                       break;
> >               if (memblock_is_nomap(reg))
> >                       continue;
> > -             if (start <= __pa(PAGE_OFFSET) &&
> > -                 __pa(PAGE_OFFSET) < end)
> > -                     start = __pa(PAGE_OFFSET);
> > +             if (start <= __pa_symbol(kernel_virt_addr) &&
> > +                 __pa(kernel_virt_addr) < end)
> > +                     start = __pa_symbol(kernel_virt_addr);

Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.

> >
> >               map_size = best_map_size(start, end - start);
> >               for (pa = start; pa < end; pa += map_size) {

Alexandre Ghiti March 22, 2020, 7:10 a.m. UTC | #4

Hi Zong,

Sorry for the response delay, please find below my comments.

On 3/12/20 1:57 AM, Zong Li wrote:
> On Sat, Mar 7, 2020 at 1:58 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>>
>> On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
>>> This config allows to compile the kernel as PIE and to relocate it at any
>>> virtual address at runtime: this paves the way to KASLR and to 4-level
>>> page table folding at runtime. Runtime relocation is possible since
>>> relocation metadata are embedded into the kernel.
>>>
>>> Note that relocating at runtime introduces an overhead even if the kernel
>>> is loaded at the same address it was linked at and that the compiler
>>> options are those used in arm64 which uses the same RELA relocation format.
>>>
>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>>> Reviewed-by: Zong Li <zong.li@sifive.com>
>>> Reviewed-by: Anup Patel <anup@brainfault.org>
>>> Tested-by: Zong Li <zong.li@sifive.com>
>>> ---
>>> Changes in v2:
>>> - Make RELOCATABLE depend on MMU as suggested by Anup
>>> - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
>>> - Use __pa_symbol instead of __pa, as suggested by Zong
>>> - Rebased on top of v5.6-rc3
>>> - Tested with sv48 patchset
>>> - Add Reviewed/Tested-by from Zong and Anup
>>>
>>>   arch/riscv/Kconfig              | 12 +++++
>>>   arch/riscv/Makefile             |  5 +-
>>>   arch/riscv/boot/loader.lds.S    |  2 +-
>>>   arch/riscv/include/asm/page.h   |  5 +-
>>>   arch/riscv/kernel/head.S        |  3 +-
>>>   arch/riscv/kernel/vmlinux.lds.S | 10 ++--
>>>   arch/riscv/mm/Makefile          |  4 ++
>>>   arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
>>>   8 files changed, 111 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index 73f029eae0cc..f5f3d474504d 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
>>>        default 3 if 64BIT
>>>        default 2
>>>
>>> +config RELOCATABLE
>>> +     bool
>>> +     depends on MMU
>>> +     help
>>> +          This builds a kernel as a Position Independent Executable (PIE),
>>> +          which retains all relocation metadata required to relocate the
>>> +          kernel binary at runtime to a different virtual address than the
>>> +          address it was linked at.
>>> +          Since RISCV uses the RELA relocation format, this requires a
>>> +          relocation pass at runtime even if the kernel is loaded at the
>>> +          same address it was linked at.
>>> +
>>>   source "arch/riscv/Kconfig.socs"
>>>
>>>   menu "Platform type"
>>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>>> index b9009a2fbaf5..5a115cf6a9c1 100644
>>> --- a/arch/riscv/Makefile
>>> +++ b/arch/riscv/Makefile
>>> @@ -9,7 +9,10 @@
>>>   #
>>>
>>>   OBJCOPYFLAGS    := -O binary
>>> -LDFLAGS_vmlinux :=
>>> +ifeq ($(CONFIG_RELOCATABLE),y)
>>> +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
>>> +KBUILD_CFLAGS += -fPIE
>>> +endif
>>>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>>>        LDFLAGS_vmlinux := --no-relax
>>>   endif
>>> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
>>> index 47a5003c2e28..a9ed218171aa 100644
>>> --- a/arch/riscv/boot/loader.lds.S
>>> +++ b/arch/riscv/boot/loader.lds.S
>>> @@ -7,7 +7,7 @@ ENTRY(_start)
>>>
>>>   SECTIONS
>>>   {
>>> -     . = PAGE_OFFSET;
>>> +     . = CONFIG_PAGE_OFFSET;
>>>
>>>        .payload : {
>>>                *(.payload)
>>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
>>> index 8ca1930caa44..af5810f9aebd 100644
>>> --- a/arch/riscv/include/asm/page.h
>>> +++ b/arch/riscv/include/asm/page.h
>>> @@ -31,9 +31,9 @@
>>>    * When not using MMU this corresponds to the first free page in
>>>    * physical memory (aligned on a page boundary).
>>>    */
>>> -#define PAGE_OFFSET          _AC(CONFIG_PAGE_OFFSET, UL)
>>> +#define PAGE_OFFSET          kernel_virt_addr
>>
>> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
>> systems.  As it currently stands this is imposing a performance hit even when
>>
> 
> I had almost done the KASLR implementation on top of this patch.
> Actually, PAGE_OFFSET change is unnecessary in KASLR , because we
> would move kernel image to a random physical address as well, so the
> $pc will go to the relevant random virtual address. We need

I don't understand what you mean here, can you explain it a bit more ?

> kernel_virt_addr to record the new destination, but keep PAGE_OFFSET
> to be CONFIG_PAGE_OFFSET is enough.

 From my understanding, PAGE_OFFSET should represent the start of the 
direct mapping, so in case of a relocatable kernel, its value should 
reflect the offset too.

Is there any issue with having PAGE_OFFSET equal to kernel_virt_addr ?

If we use both, we will need to know precisely when we should use 
kernel_virt_addr or PAGE_OFFSET, which I think will be painful and error 
prone.

> 
>>> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
>>> +#define KERN_VIRT_SIZE               (-_AC(CONFIG_PAGE_OFFSET, UL))
>>
>> This seems like it would cause issues if the kernel is relocated to high enough
>> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.
>>
> 
> Based on the same reason, keep KERN_VIRT_SIZE to be -PAGE_OFFSET is good.
> 
>>>   #ifndef __ASSEMBLY__
>>>
>>> @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
>>>   #define ARCH_PFN_OFFSET              (PAGE_OFFSET >> PAGE_SHIFT)
>>>   #endif /* CONFIG_MMU */
>>>
>>> +extern unsigned long kernel_virt_addr;
>>>   extern unsigned long max_low_pfn;
>>>   extern unsigned long min_low_pfn;
>>>
>>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>>> index 271860fc2c3f..d792912c2da3 100644
>>> --- a/arch/riscv/kernel/head.S
>>> +++ b/arch/riscv/kernel/head.S
>>> @@ -131,7 +131,8 @@ clear_bss_done:
>>>   #ifdef CONFIG_MMU
>>>   relocate:
>>>        /* Relocate return address */
>>> -     li a1, PAGE_OFFSET
>>> +     la a1, kernel_virt_addr
>>> +     REG_L a1, 0(a1)
>>>        la a2, _start
>>>        sub a1, a1, a2
>>>        add ra, ra, a1
>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>>> index 1e0193ded420..5bf69e9b91e6 100644
>>> --- a/arch/riscv/kernel/vmlinux.lds.S
>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>>> @@ -4,7 +4,7 @@
>>>    * Copyright (C) 2017 SiFive
>>>    */
>>>
>>> -#define LOAD_OFFSET PAGE_OFFSET
>>> +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
>>>   #include <asm/vmlinux.lds.h>
>>>   #include <asm/page.h>
>>>   #include <asm/cache.h>
>>> @@ -71,9 +71,11 @@ SECTIONS
>>>
>>>        EXCEPTION_TABLE(0x10)
>>>
>>> -     .rel.dyn : {
>>> -             *(.rel.dyn*)
>>> -     }
>>> +        .rela.dyn : ALIGN(8) {
>>> +             __rela_dyn_start = .;
>>> +                *(.rela .rela*)
>>> +             __rela_dyn_end = .;
>>> +        }
>>
>> It looks like the indentation is screwed up here: I see a mix of tabs/spaces
>> that doesn't match the rest of the file.
>>
>>>
>>>        _end = .;
>>>
>>> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
>>> index 50b7af58c566..27593d362248 100644
>>> --- a/arch/riscv/mm/Makefile
>>> +++ b/arch/riscv/mm/Makefile
>>> @@ -1,6 +1,10 @@
>>>   # SPDX-License-Identifier: GPL-2.0-only
>>>
>>>   CFLAGS_init.o := -mcmodel=medany
>>> +ifdef CONFIG_RELOCATABLE
>>> +CFLAGS_init.o += -fno-pie
>>> +endif
>>> +
>>>   ifdef CONFIG_FTRACE
>>>   CFLAGS_REMOVE_init.o = -pg
>>>   endif
>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>> index 965a8cf4829c..428aee2669aa 100644
>>> --- a/arch/riscv/mm/init.c
>>> +++ b/arch/riscv/mm/init.c
>>> @@ -12,6 +12,9 @@
>>>   #include <linux/sizes.h>
>>>   #include <linux/of_fdt.h>
>>>   #include <linux/libfdt.h>
>>> +#ifdef CONFIG_RELOCATABLE
>>> +#include <linux/elf.h>
>>> +#endif
>>>
>>>   #include <asm/fixmap.h>
>>>   #include <asm/tlbflush.h>
>>> @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
>>>   extern char _start[];
>>>   void *dtb_early_va;
>>>
>>> +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>>> +EXPORT_SYMBOL(kernel_virt_addr);
>>> +
>>>   static void __init zone_sizes_init(void)
>>>   {
>>>        unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
>>> @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
>>>                phys_addr_t end = reg->base + reg->size;
>>>
>>>                if (reg->base <= vmlinux_end && vmlinux_end <= end) {
>>> -                     mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
>>> +                     mem_size = min(reg->size,
>>> +                                    (phys_addr_t)-kernel_virt_addr);
>>
>> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these --
>> they account for a significant fraction of the diff.
>>
> 
> kernel_virt_addr would be assigned to a random destination by KASLR,
> but here still should be PAGE_OFFSET rather than kernel_virt_addr as
> mentioned above.
> 
>>>                        /*
>>>                         * Remove memblock from the end of usable area to the
>>> @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>>>        if (mmu_enabled)
>>>                return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>>
>>> -     pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>>> +     pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
> 
> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
> 
>>>        BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>>>        return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>>>   }
>>> @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>>>   #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
>>>   #endif
>>>
>>> +#ifdef CONFIG_RELOCATABLE
>>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
>>> +
>>> +#ifdef CONFIG_64BIT
>>> +#define Elf_Rela Elf64_Rela
>>> +#define Elf_Addr Elf64_Addr
>>> +#else
>>> +#define Elf_Rela Elf32_Rela
>>> +#define Elf_Addr Elf32_Addr
>>> +#endif
>>> +
>>> +void __init relocate_kernel(uintptr_t load_pa)
>>> +{
>>> +     Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
>>> +     uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>>> +     /*
>>> +      * This holds the offset between the linked virtual address and the
>>> +      * relocated virtual address.
>>> +      */
>>> +     uintptr_t reloc_offset = kernel_virt_addr - link_addr;
>>> +     /*
>>> +      * This holds the offset between linked virtual address and physical
>>> +      * address whereas va_pa_offset holds the offset between relocated
>>> +      * virtual address and physical address.
>>> +      */
>>> +     uintptr_t va_link_pa_offset = link_addr - load_pa;
>>> +
>>> +     for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
>>> +             Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
>>> +             Elf_Addr relocated_addr = rela->r_addend;
>>> +
>>> +             if (rela->r_info != R_RISCV_RELATIVE)
>>> +                     continue;
>>
>> This should at least provide a warning when it encounters an unresolvable
>> relocation.  Is it currently stands this just ignores all other runtime
>> relocations, and while I can buy the argument there shouldn't be any (though
>> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently
>> skip them.
>>
>>> +
>>> +             /*
>>> +              * Make sure to not relocate vdso symbols like rt_sigreturn
>>> +              * which are linked from the address 0 in vmlinux since
>>> +              * vdso symbol addresses are actually used as an offset from
>>> +              * mm->context.vdso in VDSO_OFFSET macro.
>>> +              */
>>> +             if (relocated_addr >= link_addr)
>>> +                     relocated_addr += reloc_offset;
>>> +
>>> +             *(Elf_Addr *)addr = relocated_addr;
>>> +     }
>>> +}
>>> +#endif
>>> +
>>>   asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>   {
>>>        uintptr_t va, end_va;
>>> @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>        uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>>>        uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>>>
>>> -     va_pa_offset = PAGE_OFFSET - load_pa;
>>> +     va_pa_offset = kernel_virt_addr - load_pa;
>>>        pfn_base = PFN_DOWN(load_pa);
>>>
>>> +#ifdef CONFIG_RELOCATABLE
>>> +     /*
>>> +      * Early page table uses only one PGDIR, which makes it possible
>>> +      * to map 1GB aligned on 1GB: if the relocation offset makes the kernel
>>> +      * cross over a 1G boundary, raise a bug since a part of the kernel
>>> +      * would not get mapped.
>>> +      */
>>> +     BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
>>> +     relocate_kernel(load_pa);
>>> +#endif
>>> +
>>>        /*
>>>         * Enforce boot alignment requirements of RV32 and
>>>         * RV64 by only allowing PMD or PGD mappings.
>>> @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>        BUG_ON(map_size == PAGE_SIZE);
>>>
>>>        /* Sanity check alignment and size */
>>> -     BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
>>> +     BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
>>>        BUG_ON((load_pa % map_size) != 0);
>>>        BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
>>>
>>> @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>        create_pmd_mapping(fixmap_pmd, FIXADDR_START,
>>>                           (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
>>>        /* Setup trampoline PGD and PMD */
>>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>                           (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
>>> -     create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
>>> +     create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>>>                           load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>>>   #else
>>>        /* Setup trampoline PGD */
>>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>                           load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
>>>   #endif
>>>
>>> @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>         * us to reach paging_init(). We map all memory banks later
>>>         * in setup_vm_final() below.
>>>         */
>>> -     end_va = PAGE_OFFSET + load_sz;
>>> -     for (va = PAGE_OFFSET; va < end_va; va += map_size)
>>> +     end_va = kernel_virt_addr + load_sz;
>>> +     for (va = kernel_virt_addr; va < end_va; va += map_size)
>>>                create_pgd_mapping(early_pg_dir, va,
>>> -                                load_pa + (va - PAGE_OFFSET),
>>> +                                load_pa + (va - kernel_virt_addr),
>>>                                   map_size, PAGE_KERNEL_EXEC);
>>>
>>>        /* Create fixed mapping for early FDT parsing */
>>> @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
>>>                        break;
>>>                if (memblock_is_nomap(reg))
>>>                        continue;
>>> -             if (start <= __pa(PAGE_OFFSET) &&
>>> -                 __pa(PAGE_OFFSET) < end)
>>> -                     start = __pa(PAGE_OFFSET);
>>> +             if (start <= __pa_symbol(kernel_virt_addr) &&
>>> +                 __pa(kernel_virt_addr) < end)
>>> +                     start = __pa_symbol(kernel_virt_addr);
> 
> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
> 
>>>
>>>                map_size = best_map_size(start, end - start);
>>>                for (pa = start; pa < end; pa += map_size) {

Thanks,

Alex

Zong Li March 24, 2020, 7:22 a.m. UTC | #5

On Sun, Mar 22, 2020 at 3:10 PM Alex Ghiti <alex@ghiti.fr> wrote:
>
> Hi Zong,
>
> Sorry for the response delay, please find below my comments.
>
> On 3/12/20 1:57 AM, Zong Li wrote:
> > On Sat, Mar 7, 2020 at 1:58 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
> >>
> >> On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
> >>> This config allows to compile the kernel as PIE and to relocate it at any
> >>> virtual address at runtime: this paves the way to KASLR and to 4-level
> >>> page table folding at runtime. Runtime relocation is possible since
> >>> relocation metadata are embedded into the kernel.
> >>>
> >>> Note that relocating at runtime introduces an overhead even if the kernel
> >>> is loaded at the same address it was linked at and that the compiler
> >>> options are those used in arm64 which uses the same RELA relocation format.
> >>>
> >>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> >>> Reviewed-by: Zong Li <zong.li@sifive.com>
> >>> Reviewed-by: Anup Patel <anup@brainfault.org>
> >>> Tested-by: Zong Li <zong.li@sifive.com>
> >>> ---
> >>> Changes in v2:
> >>> - Make RELOCATABLE depend on MMU as suggested by Anup
> >>> - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
> >>> - Use __pa_symbol instead of __pa, as suggested by Zong
> >>> - Rebased on top of v5.6-rc3
> >>> - Tested with sv48 patchset
> >>> - Add Reviewed/Tested-by from Zong and Anup
> >>>
> >>>   arch/riscv/Kconfig              | 12 +++++
> >>>   arch/riscv/Makefile             |  5 +-
> >>>   arch/riscv/boot/loader.lds.S    |  2 +-
> >>>   arch/riscv/include/asm/page.h   |  5 +-
> >>>   arch/riscv/kernel/head.S        |  3 +-
> >>>   arch/riscv/kernel/vmlinux.lds.S | 10 ++--
> >>>   arch/riscv/mm/Makefile          |  4 ++
> >>>   arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
> >>>   8 files changed, 111 insertions(+), 22 deletions(-)
> >>>
> >>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >>> index 73f029eae0cc..f5f3d474504d 100644
> >>> --- a/arch/riscv/Kconfig
> >>> +++ b/arch/riscv/Kconfig
> >>> @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
> >>>        default 3 if 64BIT
> >>>        default 2
> >>>
> >>> +config RELOCATABLE
> >>> +     bool
> >>> +     depends on MMU
> >>> +     help
> >>> +          This builds a kernel as a Position Independent Executable (PIE),
> >>> +          which retains all relocation metadata required to relocate the
> >>> +          kernel binary at runtime to a different virtual address than the
> >>> +          address it was linked at.
> >>> +          Since RISCV uses the RELA relocation format, this requires a
> >>> +          relocation pass at runtime even if the kernel is loaded at the
> >>> +          same address it was linked at.
> >>> +
> >>>   source "arch/riscv/Kconfig.socs"
> >>>
> >>>   menu "Platform type"
> >>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> >>> index b9009a2fbaf5..5a115cf6a9c1 100644
> >>> --- a/arch/riscv/Makefile
> >>> +++ b/arch/riscv/Makefile
> >>> @@ -9,7 +9,10 @@
> >>>   #
> >>>
> >>>   OBJCOPYFLAGS    := -O binary
> >>> -LDFLAGS_vmlinux :=
> >>> +ifeq ($(CONFIG_RELOCATABLE),y)
> >>> +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
> >>> +KBUILD_CFLAGS += -fPIE
> >>> +endif
> >>>   ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
> >>>        LDFLAGS_vmlinux := --no-relax
> >>>   endif
> >>> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
> >>> index 47a5003c2e28..a9ed218171aa 100644
> >>> --- a/arch/riscv/boot/loader.lds.S
> >>> +++ b/arch/riscv/boot/loader.lds.S
> >>> @@ -7,7 +7,7 @@ ENTRY(_start)
> >>>
> >>>   SECTIONS
> >>>   {
> >>> -     . = PAGE_OFFSET;
> >>> +     . = CONFIG_PAGE_OFFSET;
> >>>
> >>>        .payload : {
> >>>                *(.payload)
> >>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> >>> index 8ca1930caa44..af5810f9aebd 100644
> >>> --- a/arch/riscv/include/asm/page.h
> >>> +++ b/arch/riscv/include/asm/page.h
> >>> @@ -31,9 +31,9 @@
> >>>    * When not using MMU this corresponds to the first free page in
> >>>    * physical memory (aligned on a page boundary).
> >>>    */
> >>> -#define PAGE_OFFSET          _AC(CONFIG_PAGE_OFFSET, UL)
> >>> +#define PAGE_OFFSET          kernel_virt_addr
> >>
> >> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
> >> systems.  As it currently stands this is imposing a performance hit even when
> >>
> >
> > I had almost done the KASLR implementation on top of this patch.
> > Actually, PAGE_OFFSET change is unnecessary in KASLR , because we
> > would move kernel image to a random physical address as well, so the
> > $pc will go to the relevant random virtual address. We need
>
> I don't understand what you mean here, can you explain it a bit more ?
>
> > kernel_virt_addr to record the new destination, but keep PAGE_OFFSET
> > to be CONFIG_PAGE_OFFSET is enough.
>
>  From my understanding, PAGE_OFFSET should represent the start of the
> direct mapping, so in case of a relocatable kernel, its value should
> reflect the offset too.
>

Let me try to use the common RISC-V case to explain that.

In this v2 version, we could use a random virtual address to map the
kernel image which is located in 0x8020_0000 physical address, then we
could achieve the purpose of randomization, but it only happens on
virtual address, the kernel image is still in 0x8020_0000 physical
address, so we would also try to move the physical location of kernel
image by a random offset.

For example, assume there is a 1G size DDR, the kernel image size is
10MB and we get a random kernel offset 0x100_0000, finally, kernel
image would locate in 0x8120_0000, and run on corresponding virtual
address 0xffff_ffe0_0100_0000 in CPU view. The direct mapping range is
still got from 0x8020_0000 to 0xc000_0000, that means, there are
available free pages from 0x8020_0000 to 0x811f_ffff, and a reserved
region for kernel image from 0x8120_0000 to 0x81c0_0000, the rest of
the memory are free pages as well (in fact, there are other reserved
regions such as dtb, initrd and so on). Hence, we don't change
PAGE_OFFSET, the PAGE_OFFSET still represent the start of the direct
mapping as you mentioned, but the location of kernel image which in
direct mapping would be unpredictable.

> Is there any issue with having PAGE_OFFSET equal to kernel_virt_addr ?

If we make PAGE_OFFSET be the new random kernel start address, the
system would lose the part of memory after we also moving kernel image
to a new physical location, that means, the memory which prior of new
random kernel start address is disappeared, because some reasons like
it only creates page table start from new physical address, the
memblock only sees the memory from __pa(PAGE_OFFSET), and etc.

>
> If we use both, we will need to know precisely when we should use
> kernel_virt_addr or PAGE_OFFSET, which I think will be painful and error
> prone.

There is a use case, we could get kernel offset by the expression
'kernel_virt_addr - PAGE_OFFSET'.

It seems to me that I could post the RFC patches first, but it depends
on other patch series, include your relocation implementation.

>
> >
> >>> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
> >>> +#define KERN_VIRT_SIZE               (-_AC(CONFIG_PAGE_OFFSET, UL))
> >>
> >> This seems like it would cause issues if the kernel is relocated to high enough
> >> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.
> >>
> >
> > Based on the same reason, keep KERN_VIRT_SIZE to be -PAGE_OFFSET is good.
> >
> >>>   #ifndef __ASSEMBLY__
> >>>
> >>> @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
> >>>   #define ARCH_PFN_OFFSET              (PAGE_OFFSET >> PAGE_SHIFT)
> >>>   #endif /* CONFIG_MMU */
> >>>
> >>> +extern unsigned long kernel_virt_addr;
> >>>   extern unsigned long max_low_pfn;
> >>>   extern unsigned long min_low_pfn;
> >>>
> >>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> >>> index 271860fc2c3f..d792912c2da3 100644
> >>> --- a/arch/riscv/kernel/head.S
> >>> +++ b/arch/riscv/kernel/head.S
> >>> @@ -131,7 +131,8 @@ clear_bss_done:
> >>>   #ifdef CONFIG_MMU
> >>>   relocate:
> >>>        /* Relocate return address */
> >>> -     li a1, PAGE_OFFSET
> >>> +     la a1, kernel_virt_addr
> >>> +     REG_L a1, 0(a1)
> >>>        la a2, _start
> >>>        sub a1, a1, a2
> >>>        add ra, ra, a1
> >>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> >>> index 1e0193ded420..5bf69e9b91e6 100644
> >>> --- a/arch/riscv/kernel/vmlinux.lds.S
> >>> +++ b/arch/riscv/kernel/vmlinux.lds.S
> >>> @@ -4,7 +4,7 @@
> >>>    * Copyright (C) 2017 SiFive
> >>>    */
> >>>
> >>> -#define LOAD_OFFSET PAGE_OFFSET
> >>> +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
> >>>   #include <asm/vmlinux.lds.h>
> >>>   #include <asm/page.h>
> >>>   #include <asm/cache.h>
> >>> @@ -71,9 +71,11 @@ SECTIONS
> >>>
> >>>        EXCEPTION_TABLE(0x10)
> >>>
> >>> -     .rel.dyn : {
> >>> -             *(.rel.dyn*)
> >>> -     }
> >>> +        .rela.dyn : ALIGN(8) {
> >>> +             __rela_dyn_start = .;
> >>> +                *(.rela .rela*)
> >>> +             __rela_dyn_end = .;
> >>> +        }
> >>
> >> It looks like the indentation is screwed up here: I see a mix of tabs/spaces
> >> that doesn't match the rest of the file.
> >>
> >>>
> >>>        _end = .;
> >>>
> >>> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> >>> index 50b7af58c566..27593d362248 100644
> >>> --- a/arch/riscv/mm/Makefile
> >>> +++ b/arch/riscv/mm/Makefile
> >>> @@ -1,6 +1,10 @@
> >>>   # SPDX-License-Identifier: GPL-2.0-only
> >>>
> >>>   CFLAGS_init.o := -mcmodel=medany
> >>> +ifdef CONFIG_RELOCATABLE
> >>> +CFLAGS_init.o += -fno-pie
> >>> +endif
> >>> +
> >>>   ifdef CONFIG_FTRACE
> >>>   CFLAGS_REMOVE_init.o = -pg
> >>>   endif
> >>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> >>> index 965a8cf4829c..428aee2669aa 100644
> >>> --- a/arch/riscv/mm/init.c
> >>> +++ b/arch/riscv/mm/init.c
> >>> @@ -12,6 +12,9 @@
> >>>   #include <linux/sizes.h>
> >>>   #include <linux/of_fdt.h>
> >>>   #include <linux/libfdt.h>
> >>> +#ifdef CONFIG_RELOCATABLE
> >>> +#include <linux/elf.h>
> >>> +#endif
> >>>
> >>>   #include <asm/fixmap.h>
> >>>   #include <asm/tlbflush.h>
> >>> @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
> >>>   extern char _start[];
> >>>   void *dtb_early_va;
> >>>
> >>> +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> >>> +EXPORT_SYMBOL(kernel_virt_addr);
> >>> +
> >>>   static void __init zone_sizes_init(void)
> >>>   {
> >>>        unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
> >>> @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
> >>>                phys_addr_t end = reg->base + reg->size;
> >>>
> >>>                if (reg->base <= vmlinux_end && vmlinux_end <= end) {
> >>> -                     mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
> >>> +                     mem_size = min(reg->size,
> >>> +                                    (phys_addr_t)-kernel_virt_addr);
> >>
> >> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these --
> >> they account for a significant fraction of the diff.
> >>
> >
> > kernel_virt_addr would be assigned to a random destination by KASLR,
> > but here still should be PAGE_OFFSET rather than kernel_virt_addr as
> > mentioned above.
> >
> >>>                        /*
> >>>                         * Remove memblock from the end of usable area to the
> >>> @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
> >>>        if (mmu_enabled)
> >>>                return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> >>>
> >>> -     pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> >>> +     pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
> >
> > Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
> >
> >>>        BUG_ON(pmd_num >= NUM_EARLY_PMDS);
> >>>        return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
> >>>   }
> >>> @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> >>>   #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
> >>>   #endif
> >>>
> >>> +#ifdef CONFIG_RELOCATABLE
> >>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
> >>> +
> >>> +#ifdef CONFIG_64BIT
> >>> +#define Elf_Rela Elf64_Rela
> >>> +#define Elf_Addr Elf64_Addr
> >>> +#else
> >>> +#define Elf_Rela Elf32_Rela
> >>> +#define Elf_Addr Elf32_Addr
> >>> +#endif
> >>> +
> >>> +void __init relocate_kernel(uintptr_t load_pa)
> >>> +{
> >>> +     Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
> >>> +     uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
> >>> +     /*
> >>> +      * This holds the offset between the linked virtual address and the
> >>> +      * relocated virtual address.
> >>> +      */
> >>> +     uintptr_t reloc_offset = kernel_virt_addr - link_addr;
> >>> +     /*
> >>> +      * This holds the offset between linked virtual address and physical
> >>> +      * address whereas va_pa_offset holds the offset between relocated
> >>> +      * virtual address and physical address.
> >>> +      */
> >>> +     uintptr_t va_link_pa_offset = link_addr - load_pa;
> >>> +
> >>> +     for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
> >>> +             Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
> >>> +             Elf_Addr relocated_addr = rela->r_addend;
> >>> +
> >>> +             if (rela->r_info != R_RISCV_RELATIVE)
> >>> +                     continue;
> >>
> >> This should at least provide a warning when it encounters an unresolvable
> >> relocation.  Is it currently stands this just ignores all other runtime
> >> relocations, and while I can buy the argument there shouldn't be any (though
> >> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently
> >> skip them.
> >>
> >>> +
> >>> +             /*
> >>> +              * Make sure to not relocate vdso symbols like rt_sigreturn
> >>> +              * which are linked from the address 0 in vmlinux since
> >>> +              * vdso symbol addresses are actually used as an offset from
> >>> +              * mm->context.vdso in VDSO_OFFSET macro.
> >>> +              */
> >>> +             if (relocated_addr >= link_addr)
> >>> +                     relocated_addr += reloc_offset;
> >>> +
> >>> +             *(Elf_Addr *)addr = relocated_addr;
> >>> +     }
> >>> +}
> >>> +#endif
> >>> +
> >>>   asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >>>   {
> >>>        uintptr_t va, end_va;
> >>> @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >>>        uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
> >>>        uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> >>>
> >>> -     va_pa_offset = PAGE_OFFSET - load_pa;
> >>> +     va_pa_offset = kernel_virt_addr - load_pa;
> >>>        pfn_base = PFN_DOWN(load_pa);
> >>>
> >>> +#ifdef CONFIG_RELOCATABLE
> >>> +     /*
> >>> +      * Early page table uses only one PGDIR, which makes it possible
> >>> +      * to map 1GB aligned on 1GB: if the relocation offset makes the kernel
> >>> +      * cross over a 1G boundary, raise a bug since a part of the kernel
> >>> +      * would not get mapped.
> >>> +      */
> >>> +     BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
> >>> +     relocate_kernel(load_pa);
> >>> +#endif
> >>> +
> >>>        /*
> >>>         * Enforce boot alignment requirements of RV32 and
> >>>         * RV64 by only allowing PMD or PGD mappings.
> >>> @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >>>        BUG_ON(map_size == PAGE_SIZE);
> >>>
> >>>        /* Sanity check alignment and size */
> >>> -     BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
> >>> +     BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
> >>>        BUG_ON((load_pa % map_size) != 0);
> >>>        BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
> >>>
> >>> @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >>>        create_pmd_mapping(fixmap_pmd, FIXADDR_START,
> >>>                           (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
> >>>        /* Setup trampoline PGD and PMD */
> >>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> >>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
> >>>                           (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
> >>> -     create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
> >>> +     create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
> >>>                           load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
> >>>   #else
> >>>        /* Setup trampoline PGD */
> >>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
> >>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
> >>>                           load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
> >>>   #endif
> >>>
> >>> @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> >>>         * us to reach paging_init(). We map all memory banks later
> >>>         * in setup_vm_final() below.
> >>>         */
> >>> -     end_va = PAGE_OFFSET + load_sz;
> >>> -     for (va = PAGE_OFFSET; va < end_va; va += map_size)
> >>> +     end_va = kernel_virt_addr + load_sz;
> >>> +     for (va = kernel_virt_addr; va < end_va; va += map_size)
> >>>                create_pgd_mapping(early_pg_dir, va,
> >>> -                                load_pa + (va - PAGE_OFFSET),
> >>> +                                load_pa + (va - kernel_virt_addr),
> >>>                                   map_size, PAGE_KERNEL_EXEC);
> >>>
> >>>        /* Create fixed mapping for early FDT parsing */
> >>> @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
> >>>                        break;
> >>>                if (memblock_is_nomap(reg))
> >>>                        continue;
> >>> -             if (start <= __pa(PAGE_OFFSET) &&
> >>> -                 __pa(PAGE_OFFSET) < end)
> >>> -                     start = __pa(PAGE_OFFSET);
> >>> +             if (start <= __pa_symbol(kernel_virt_addr) &&
> >>> +                 __pa(kernel_virt_addr) < end)
> >>> +                     start = __pa_symbol(kernel_virt_addr);
> >
> > Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
> >
> >>>
> >>>                map_size = best_map_size(start, end - start);
> >>>                for (pa = start; pa < end; pa += map_size) {
>
> Thanks,
>
> Alex

Alexandre Ghiti March 29, 2020, 4:15 p.m. UTC | #6

Hi Zong,

On 3/24/20 3:22 AM, Zong Li wrote:
> On Sun, Mar 22, 2020 at 3:10 PM Alex Ghiti <alex@ghiti.fr> wrote:
>>
>> Hi Zong,
>>
>> Sorry for the response delay, please find below my comments.
>>
>> On 3/12/20 1:57 AM, Zong Li wrote:
>>> On Sat, Mar 7, 2020 at 1:58 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>>>>
>>>> On Mon, 02 Mar 2020 21:44:37 PST (-0800), alex@ghiti.fr wrote:
>>>>> This config allows to compile the kernel as PIE and to relocate it at any
>>>>> virtual address at runtime: this paves the way to KASLR and to 4-level
>>>>> page table folding at runtime. Runtime relocation is possible since
>>>>> relocation metadata are embedded into the kernel.
>>>>>
>>>>> Note that relocating at runtime introduces an overhead even if the kernel
>>>>> is loaded at the same address it was linked at and that the compiler
>>>>> options are those used in arm64 which uses the same RELA relocation format.
>>>>>
>>>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>>>>> Reviewed-by: Zong Li <zong.li@sifive.com>
>>>>> Reviewed-by: Anup Patel <anup@brainfault.org>
>>>>> Tested-by: Zong Li <zong.li@sifive.com>
>>>>> ---
>>>>> Changes in v2:
>>>>> - Make RELOCATABLE depend on MMU as suggested by Anup
>>>>> - Rename kernel_load_addr into kernel_virt_addr as suggested by Anup
>>>>> - Use __pa_symbol instead of __pa, as suggested by Zong
>>>>> - Rebased on top of v5.6-rc3
>>>>> - Tested with sv48 patchset
>>>>> - Add Reviewed/Tested-by from Zong and Anup
>>>>>
>>>>>    arch/riscv/Kconfig              | 12 +++++
>>>>>    arch/riscv/Makefile             |  5 +-
>>>>>    arch/riscv/boot/loader.lds.S    |  2 +-
>>>>>    arch/riscv/include/asm/page.h   |  5 +-
>>>>>    arch/riscv/kernel/head.S        |  3 +-
>>>>>    arch/riscv/kernel/vmlinux.lds.S | 10 ++--
>>>>>    arch/riscv/mm/Makefile          |  4 ++
>>>>>    arch/riscv/mm/init.c            | 92 ++++++++++++++++++++++++++++-----
>>>>>    8 files changed, 111 insertions(+), 22 deletions(-)
>>>>>
>>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>>>> index 73f029eae0cc..f5f3d474504d 100644
>>>>> --- a/arch/riscv/Kconfig
>>>>> +++ b/arch/riscv/Kconfig
>>>>> @@ -163,6 +163,18 @@ config PGTABLE_LEVELS
>>>>>         default 3 if 64BIT
>>>>>         default 2
>>>>>
>>>>> +config RELOCATABLE
>>>>> +     bool
>>>>> +     depends on MMU
>>>>> +     help
>>>>> +          This builds a kernel as a Position Independent Executable (PIE),
>>>>> +          which retains all relocation metadata required to relocate the
>>>>> +          kernel binary at runtime to a different virtual address than the
>>>>> +          address it was linked at.
>>>>> +          Since RISCV uses the RELA relocation format, this requires a
>>>>> +          relocation pass at runtime even if the kernel is loaded at the
>>>>> +          same address it was linked at.
>>>>> +
>>>>>    source "arch/riscv/Kconfig.socs"
>>>>>
>>>>>    menu "Platform type"
>>>>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>>>>> index b9009a2fbaf5..5a115cf6a9c1 100644
>>>>> --- a/arch/riscv/Makefile
>>>>> +++ b/arch/riscv/Makefile
>>>>> @@ -9,7 +9,10 @@
>>>>>    #
>>>>>
>>>>>    OBJCOPYFLAGS    := -O binary
>>>>> -LDFLAGS_vmlinux :=
>>>>> +ifeq ($(CONFIG_RELOCATABLE),y)
>>>>> +LDFLAGS_vmlinux := -shared -Bsymbolic -z notext -z norelro
>>>>> +KBUILD_CFLAGS += -fPIE
>>>>> +endif
>>>>>    ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>>>>>         LDFLAGS_vmlinux := --no-relax
>>>>>    endif
>>>>> diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
>>>>> index 47a5003c2e28..a9ed218171aa 100644
>>>>> --- a/arch/riscv/boot/loader.lds.S
>>>>> +++ b/arch/riscv/boot/loader.lds.S
>>>>> @@ -7,7 +7,7 @@ ENTRY(_start)
>>>>>
>>>>>    SECTIONS
>>>>>    {
>>>>> -     . = PAGE_OFFSET;
>>>>> +     . = CONFIG_PAGE_OFFSET;
>>>>>
>>>>>         .payload : {
>>>>>                 *(.payload)
>>>>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
>>>>> index 8ca1930caa44..af5810f9aebd 100644
>>>>> --- a/arch/riscv/include/asm/page.h
>>>>> +++ b/arch/riscv/include/asm/page.h
>>>>> @@ -31,9 +31,9 @@
>>>>>     * When not using MMU this corresponds to the first free page in
>>>>>     * physical memory (aligned on a page boundary).
>>>>>     */
>>>>> -#define PAGE_OFFSET          _AC(CONFIG_PAGE_OFFSET, UL)
>>>>> +#define PAGE_OFFSET          kernel_virt_addr
>>>>
>>>> I assume we want to keep PAGE_OFFSET a constant for the non-relocatable
>>>> systems.  As it currently stands this is imposing a performance hit even when
>>>>
>>>
>>> I had almost done the KASLR implementation on top of this patch.
>>> Actually, PAGE_OFFSET change is unnecessary in KASLR , because we
>>> would move kernel image to a random physical address as well, so the
>>> $pc will go to the relevant random virtual address. We need
>>
>> I don't understand what you mean here, can you explain it a bit more ?
>>
>>> kernel_virt_addr to record the new destination, but keep PAGE_OFFSET
>>> to be CONFIG_PAGE_OFFSET is enough.
>>
>>   From my understanding, PAGE_OFFSET should represent the start of the
>> direct mapping, so in case of a relocatable kernel, its value should
>> reflect the offset too.
>>
> 
> Let me try to use the common RISC-V case to explain that.
> 
> In this v2 version, we could use a random virtual address to map the
> kernel image which is located in 0x8020_0000 physical address, then we
> could achieve the purpose of randomization, but it only happens on
> virtual address, the kernel image is still in 0x8020_0000 physical
> address, so we would also try to move the physical location of kernel
> image by a random offset.
> 
> For example, assume there is a 1G size DDR, the kernel image size is
> 10MB and we get a random kernel offset 0x100_0000, finally, kernel
> image would locate in 0x8120_0000, and run on corresponding virtual
> address 0xffff_ffe0_0100_0000 in CPU view. The direct mapping range is
> still got from 0x8020_0000 to 0xc000_0000, that means, there are
> available free pages from 0x8020_0000 to 0x811f_ffff, and a reserved
> region for kernel image from 0x8120_0000 to 0x81c0_0000, the rest of
> the memory are free pages as well (in fact, there are other reserved
> regions such as dtb, initrd and so on). Hence, we don't change
> PAGE_OFFSET, the PAGE_OFFSET still represent the start of the direct
> mapping as you mentioned, but the location of kernel image which in
> direct mapping would be unpredictable.
> 
>> Is there any issue with having PAGE_OFFSET equal to kernel_virt_addr ?
> 
> If we make PAGE_OFFSET be the new random kernel start address, the
> system would lose the part of memory after we also moving kernel image
> to a new physical location, that means, the memory which prior of new
> random kernel start address is disappeared, because some reasons like
> it only creates page table start from new physical address, the
> memblock only sees the memory from __pa(PAGE_OFFSET), and etc.
> 
>>
>> If we use both, we will need to know precisely when we should use
>> kernel_virt_addr or PAGE_OFFSET, which I think will be painful and error
>> prone.
> 
> There is a use case, we could get kernel offset by the expression
> 'kernel_virt_addr - PAGE_OFFSET'.
> 
> It seems to me that I could post the RFC patches first, but it depends
> on other patch series, include your relocation implementation.
> 

You are totally right, thanks for your explanation. I'll fix that in v3 
then.

I'll take a look at your KASLR implementation soon,

Thanks,

Alex

>>
>>>
>>>>> -#define KERN_VIRT_SIZE (-PAGE_OFFSET)
>>>>> +#define KERN_VIRT_SIZE               (-_AC(CONFIG_PAGE_OFFSET, UL))
>>>>
>>>> This seems like it would cause issues if the kernel is relocated to high enough
>>>> addresses that "kernel_virt_addr+KERN_VIRT_SIZE" overflows.
>>>>
>>>
>>> Based on the same reason, keep KERN_VIRT_SIZE to be -PAGE_OFFSET is good.
>>>
>>>>>    #ifndef __ASSEMBLY__
>>>>>
>>>>> @@ -97,6 +97,7 @@ extern unsigned long pfn_base;
>>>>>    #define ARCH_PFN_OFFSET              (PAGE_OFFSET >> PAGE_SHIFT)
>>>>>    #endif /* CONFIG_MMU */
>>>>>
>>>>> +extern unsigned long kernel_virt_addr;
>>>>>    extern unsigned long max_low_pfn;
>>>>>    extern unsigned long min_low_pfn;
>>>>>
>>>>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>>>>> index 271860fc2c3f..d792912c2da3 100644
>>>>> --- a/arch/riscv/kernel/head.S
>>>>> +++ b/arch/riscv/kernel/head.S
>>>>> @@ -131,7 +131,8 @@ clear_bss_done:
>>>>>    #ifdef CONFIG_MMU
>>>>>    relocate:
>>>>>         /* Relocate return address */
>>>>> -     li a1, PAGE_OFFSET
>>>>> +     la a1, kernel_virt_addr
>>>>> +     REG_L a1, 0(a1)
>>>>>         la a2, _start
>>>>>         sub a1, a1, a2
>>>>>         add ra, ra, a1
>>>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>>>>> index 1e0193ded420..5bf69e9b91e6 100644
>>>>> --- a/arch/riscv/kernel/vmlinux.lds.S
>>>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>>>>> @@ -4,7 +4,7 @@
>>>>>     * Copyright (C) 2017 SiFive
>>>>>     */
>>>>>
>>>>> -#define LOAD_OFFSET PAGE_OFFSET
>>>>> +#define LOAD_OFFSET CONFIG_PAGE_OFFSET
>>>>>    #include <asm/vmlinux.lds.h>
>>>>>    #include <asm/page.h>
>>>>>    #include <asm/cache.h>
>>>>> @@ -71,9 +71,11 @@ SECTIONS
>>>>>
>>>>>         EXCEPTION_TABLE(0x10)
>>>>>
>>>>> -     .rel.dyn : {
>>>>> -             *(.rel.dyn*)
>>>>> -     }
>>>>> +        .rela.dyn : ALIGN(8) {
>>>>> +             __rela_dyn_start = .;
>>>>> +                *(.rela .rela*)
>>>>> +             __rela_dyn_end = .;
>>>>> +        }
>>>>
>>>> It looks like the indentation is screwed up here: I see a mix of tabs/spaces
>>>> that doesn't match the rest of the file.
>>>>
>>>>>
>>>>>         _end = .;
>>>>>
>>>>> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
>>>>> index 50b7af58c566..27593d362248 100644
>>>>> --- a/arch/riscv/mm/Makefile
>>>>> +++ b/arch/riscv/mm/Makefile
>>>>> @@ -1,6 +1,10 @@
>>>>>    # SPDX-License-Identifier: GPL-2.0-only
>>>>>
>>>>>    CFLAGS_init.o := -mcmodel=medany
>>>>> +ifdef CONFIG_RELOCATABLE
>>>>> +CFLAGS_init.o += -fno-pie
>>>>> +endif
>>>>> +
>>>>>    ifdef CONFIG_FTRACE
>>>>>    CFLAGS_REMOVE_init.o = -pg
>>>>>    endif
>>>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>>>> index 965a8cf4829c..428aee2669aa 100644
>>>>> --- a/arch/riscv/mm/init.c
>>>>> +++ b/arch/riscv/mm/init.c
>>>>> @@ -12,6 +12,9 @@
>>>>>    #include <linux/sizes.h>
>>>>>    #include <linux/of_fdt.h>
>>>>>    #include <linux/libfdt.h>
>>>>> +#ifdef CONFIG_RELOCATABLE
>>>>> +#include <linux/elf.h>
>>>>> +#endif
>>>>>
>>>>>    #include <asm/fixmap.h>
>>>>>    #include <asm/tlbflush.h>
>>>>> @@ -28,6 +31,9 @@ EXPORT_SYMBOL(empty_zero_page);
>>>>>    extern char _start[];
>>>>>    void *dtb_early_va;
>>>>>
>>>>> +unsigned long kernel_virt_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>>>>> +EXPORT_SYMBOL(kernel_virt_addr);
>>>>> +
>>>>>    static void __init zone_sizes_init(void)
>>>>>    {
>>>>>         unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };
>>>>> @@ -132,7 +138,8 @@ void __init setup_bootmem(void)
>>>>>                 phys_addr_t end = reg->base + reg->size;
>>>>>
>>>>>                 if (reg->base <= vmlinux_end && vmlinux_end <= end) {
>>>>> -                     mem_size = min(reg->size, (phys_addr_t)-PAGE_OFFSET);
>>>>> +                     mem_size = min(reg->size,
>>>>> +                                    (phys_addr_t)-kernel_virt_addr);
>>>>
>>>> PAGE_OFFSET is kernel_virt_addr, so I don't see any reason to change these --
>>>> they account for a significant fraction of the diff.
>>>>
>>>
>>> kernel_virt_addr would be assigned to a random destination by KASLR,
>>> but here still should be PAGE_OFFSET rather than kernel_virt_addr as
>>> mentioned above.
>>>
>>>>>                         /*
>>>>>                          * Remove memblock from the end of usable area to the
>>>>> @@ -269,7 +276,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>>>>>         if (mmu_enabled)
>>>>>                 return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>>>>
>>>>> -     pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>>>>> +     pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
>>>
>>> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
>>>
>>>>>         BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>>>>>         return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>>>>>    }
>>>>> @@ -370,6 +377,54 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>>>>>    #error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
>>>>>    #endif
>>>>>
>>>>> +#ifdef CONFIG_RELOCATABLE
>>>>> +extern unsigned long __rela_dyn_start, __rela_dyn_end;
>>>>> +
>>>>> +#ifdef CONFIG_64BIT
>>>>> +#define Elf_Rela Elf64_Rela
>>>>> +#define Elf_Addr Elf64_Addr
>>>>> +#else
>>>>> +#define Elf_Rela Elf32_Rela
>>>>> +#define Elf_Addr Elf32_Addr
>>>>> +#endif
>>>>> +
>>>>> +void __init relocate_kernel(uintptr_t load_pa)
>>>>> +{
>>>>> +     Elf_Rela *rela = (Elf_Rela *)&__rela_dyn_start;
>>>>> +     uintptr_t link_addr = _AC(CONFIG_PAGE_OFFSET, UL);
>>>>> +     /*
>>>>> +      * This holds the offset between the linked virtual address and the
>>>>> +      * relocated virtual address.
>>>>> +      */
>>>>> +     uintptr_t reloc_offset = kernel_virt_addr - link_addr;
>>>>> +     /*
>>>>> +      * This holds the offset between linked virtual address and physical
>>>>> +      * address whereas va_pa_offset holds the offset between relocated
>>>>> +      * virtual address and physical address.
>>>>> +      */
>>>>> +     uintptr_t va_link_pa_offset = link_addr - load_pa;
>>>>> +
>>>>> +     for ( ; rela < (Elf_Rela *)&__rela_dyn_end; rela++) {
>>>>> +             Elf_Addr addr = (rela->r_offset - va_link_pa_offset);
>>>>> +             Elf_Addr relocated_addr = rela->r_addend;
>>>>> +
>>>>> +             if (rela->r_info != R_RISCV_RELATIVE)
>>>>> +                     continue;
>>>>
>>>> This should at least provide a warning when it encounters an unresolvable
>>>> relocation.  Is it currently stands this just ignores all other runtime
>>>> relocations, and while I can buy the argument there shouldn't be any (though
>>>> I'd expect R_RISCV_{32,64} to show up?) we certainly shouldn't just silently
>>>> skip them.
>>>>
>>>>> +
>>>>> +             /*
>>>>> +              * Make sure to not relocate vdso symbols like rt_sigreturn
>>>>> +              * which are linked from the address 0 in vmlinux since
>>>>> +              * vdso symbol addresses are actually used as an offset from
>>>>> +              * mm->context.vdso in VDSO_OFFSET macro.
>>>>> +              */
>>>>> +             if (relocated_addr >= link_addr)
>>>>> +                     relocated_addr += reloc_offset;
>>>>> +
>>>>> +             *(Elf_Addr *)addr = relocated_addr;
>>>>> +     }
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>>    asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>    {
>>>>>         uintptr_t va, end_va;
>>>>> @@ -377,9 +432,20 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>         uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>>>>>         uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
>>>>>
>>>>> -     va_pa_offset = PAGE_OFFSET - load_pa;
>>>>> +     va_pa_offset = kernel_virt_addr - load_pa;
>>>>>         pfn_base = PFN_DOWN(load_pa);
>>>>>
>>>>> +#ifdef CONFIG_RELOCATABLE
>>>>> +     /*
>>>>> +      * Early page table uses only one PGDIR, which makes it possible
>>>>> +      * to map 1GB aligned on 1GB: if the relocation offset makes the kernel
>>>>> +      * cross over a 1G boundary, raise a bug since a part of the kernel
>>>>> +      * would not get mapped.
>>>>> +      */
>>>>> +     BUG_ON(SZ_1G - (kernel_virt_addr & (SZ_1G - 1)) < load_sz);
>>>>> +     relocate_kernel(load_pa);
>>>>> +#endif
>>>>> +
>>>>>         /*
>>>>>          * Enforce boot alignment requirements of RV32 and
>>>>>          * RV64 by only allowing PMD or PGD mappings.
>>>>> @@ -387,7 +453,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>         BUG_ON(map_size == PAGE_SIZE);
>>>>>
>>>>>         /* Sanity check alignment and size */
>>>>> -     BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
>>>>> +     BUILD_BUG_ON((_AC(CONFIG_PAGE_OFFSET, UL) % PGDIR_SIZE) != 0);
>>>>>         BUG_ON((load_pa % map_size) != 0);
>>>>>         BUG_ON(load_sz > MAX_EARLY_MAPPING_SIZE);
>>>>>
>>>>> @@ -400,13 +466,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>         create_pmd_mapping(fixmap_pmd, FIXADDR_START,
>>>>>                            (uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
>>>>>         /* Setup trampoline PGD and PMD */
>>>>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>>>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>>>                            (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
>>>>> -     create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
>>>>> +     create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>>>>>                            load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>>>>>    #else
>>>>>         /* Setup trampoline PGD */
>>>>> -     create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>>>> +     create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>>>                            load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
>>>>>    #endif
>>>>>
>>>>> @@ -415,10 +481,10 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>          * us to reach paging_init(). We map all memory banks later
>>>>>          * in setup_vm_final() below.
>>>>>          */
>>>>> -     end_va = PAGE_OFFSET + load_sz;
>>>>> -     for (va = PAGE_OFFSET; va < end_va; va += map_size)
>>>>> +     end_va = kernel_virt_addr + load_sz;
>>>>> +     for (va = kernel_virt_addr; va < end_va; va += map_size)
>>>>>                 create_pgd_mapping(early_pg_dir, va,
>>>>> -                                load_pa + (va - PAGE_OFFSET),
>>>>> +                                load_pa + (va - kernel_virt_addr),
>>>>>                                    map_size, PAGE_KERNEL_EXEC);
>>>>>
>>>>>         /* Create fixed mapping for early FDT parsing */
>>>>> @@ -457,9 +523,9 @@ static void __init setup_vm_final(void)
>>>>>                         break;
>>>>>                 if (memblock_is_nomap(reg))
>>>>>                         continue;
>>>>> -             if (start <= __pa(PAGE_OFFSET) &&
>>>>> -                 __pa(PAGE_OFFSET) < end)
>>>>> -                     start = __pa(PAGE_OFFSET);
>>>>> +             if (start <= __pa_symbol(kernel_virt_addr) &&
>>>>> +                 __pa(kernel_virt_addr) < end)
>>>>> +                     start = __pa_symbol(kernel_virt_addr);
>>>
>>> Here is the same, please use PAGE_OFFSET instead of kernel_virt_addr.
>>>
>>>>>
>>>>>                 map_size = best_map_size(start, end - start);
>>>>>                 for (pa = start; pa < end; pa += map_size) {
>>
>> Thanks,
>>
>> Alex

[RESEND,v2] riscv: Introduce CONFIG_RELOCATABLE

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