| Message ID | 20210104155316.16259-1-toiwoton@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v9] mm: Optional full ASLR for mmap(), mremap(), vdso, stack and heap | expand |
Hi Topi,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on 2c85ebc57b3e1817b6ce1a6b703928e113a90442]
url: https://github.com/0day-ci/linux/commits/Topi-Miettinen/mm-Optional-full-ASLR-for-mmap-mremap-vdso-stack-and-heap/20210104-235438
base: 2c85ebc57b3e1817b6ce1a6b703928e113a90442
config: powerpc-randconfig-s032-20210105 (attached as .config)
compiler: powerpc64-linux-gcc (GCC) 9.3.0
reproduce:
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# apt-get install sparse
# sparse version: v0.6.3-184-g1b896707-dirty
# https://github.com/0day-ci/linux/commit/d65e085d04e2aace153b42d29d44f3711481c9ad
git remote add linux-review https://github.com/0day-ci/linux
git fetch --no-tags linux-review Topi-Miettinen/mm-Optional-full-ASLR-for-mmap-mremap-vdso-stack-and-heap/20210104-235438
git checkout d65e085d04e2aace153b42d29d44f3711481c9ad
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' ARCH=powerpc
If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
In file included from include/linux/mman.h:5,
from arch/powerpc/kernel/asm-offsets.c:21:
include/linux/mm.h: In function 'can_randomize_full':
>> include/linux/mm.h:2995:35: error: 'ADDR_NO_RANDOMIZE' undeclared (first use in this function); did you mean 'KERN_RANDOMIZE'?
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~
| KERN_RANDOMIZE
include/linux/mm.h:2995:35: note: each undeclared identifier is reported only once for each function it appears in
>> include/linux/mm.h:2995:55: error: 'ADDR_COMPAT_LAYOUT' undeclared (first use in this function)
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:9: error: 'ADDR_LIMIT_32BIT' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:28: error: 'ADDR_LIMIT_3GB' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~
>> include/linux/mm.h:2997:36: error: implicit declaration of function 'in_32bit_syscall'; did you mean 'in_compat_syscall'? [-Werror=implicit-function-declaration]
2997 | && !(IS_ENABLED(CONFIG_64BIT) && in_32bit_syscall())
| ^~~~~~~~~~~~~~~~
| in_compat_syscall
cc1: some warnings being treated as errors
--
In file included from include/linux/mman.h:5,
from arch/powerpc/kernel/asm-offsets.c:21:
include/linux/mm.h: In function 'can_randomize_full':
>> include/linux/mm.h:2995:35: error: 'ADDR_NO_RANDOMIZE' undeclared (first use in this function); did you mean 'KERN_RANDOMIZE'?
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~
| KERN_RANDOMIZE
include/linux/mm.h:2995:35: note: each undeclared identifier is reported only once for each function it appears in
>> include/linux/mm.h:2995:55: error: 'ADDR_COMPAT_LAYOUT' undeclared (first use in this function)
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:9: error: 'ADDR_LIMIT_32BIT' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:28: error: 'ADDR_LIMIT_3GB' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~
>> include/linux/mm.h:2997:36: error: implicit declaration of function 'in_32bit_syscall'; did you mean 'in_compat_syscall'? [-Werror=implicit-function-declaration]
2997 | && !(IS_ENABLED(CONFIG_64BIT) && in_32bit_syscall())
| ^~~~~~~~~~~~~~~~
| in_compat_syscall
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:117: arch/powerpc/kernel/asm-offsets.s] Error 1
make[2]: Target '__build' not remade because of errors.
make[1]: *** [Makefile:1206: prepare0] Error 2
make[1]: Target 'modules_prepare' not remade because of errors.
make: *** [Makefile:185: __sub-make] Error 2
make: Target 'modules_prepare' not remade because of errors.
--
scripts/genksyms/parse.y: warning: 9 shift/reduce conflicts [-Wconflicts-sr]
scripts/genksyms/parse.y: warning: 5 reduce/reduce conflicts [-Wconflicts-rr]
In file included from include/linux/mman.h:5,
from arch/powerpc/kernel/asm-offsets.c:21:
include/linux/mm.h: In function 'can_randomize_full':
>> include/linux/mm.h:2995:35: error: 'ADDR_NO_RANDOMIZE' undeclared (first use in this function); did you mean 'KERN_RANDOMIZE'?
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~
| KERN_RANDOMIZE
include/linux/mm.h:2995:35: note: each undeclared identifier is reported only once for each function it appears in
>> include/linux/mm.h:2995:55: error: 'ADDR_COMPAT_LAYOUT' undeclared (first use in this function)
2995 | return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
| ^~~~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:9: error: 'ADDR_LIMIT_32BIT' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~~~
>> include/linux/mm.h:2996:28: error: 'ADDR_LIMIT_3GB' undeclared (first use in this function)
2996 | | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
| ^~~~~~~~~~~~~~
>> include/linux/mm.h:2997:36: error: implicit declaration of function 'in_32bit_syscall'; did you mean 'in_compat_syscall'? [-Werror=implicit-function-declaration]
2997 | && !(IS_ENABLED(CONFIG_64BIT) && in_32bit_syscall())
| ^~~~~~~~~~~~~~~~
| in_compat_syscall
cc1: some warnings being treated as errors
make[2]: *** [scripts/Makefile.build:117: arch/powerpc/kernel/asm-offsets.s] Error 1
make[2]: Target '__build' not remade because of errors.
make[1]: *** [Makefile:1206: prepare0] Error 2
make[1]: Target 'prepare' not remade because of errors.
make: *** [Makefile:185: __sub-make] Error 2
make: Target 'prepare' not remade because of errors.
vim +2995 include/linux/mm.h
2986
2987 #ifndef CONFIG_MMU
2988 #define randomize_va_space 0
2989 static inline bool can_randomize_full(void) { return false; }
2990 #else
2991 extern int randomize_va_space;
2992 static inline bool can_randomize_full(void)
2993 {
2994 /* Don't randomize 32 bit applications */
> 2995 return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT
> 2996 | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB))
> 2997 && !(IS_ENABLED(CONFIG_64BIT) && in_32bit_syscall())
2998 && randomize_va_space == 3;
2999 }
3000 #endif
3001
---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
On 4.1.2021 17.53, Topi Miettinen wrote: > Writing a new value of 3 to /proc/sys/kernel/randomize_va_space > enables full randomization of memory mappings. With 2, the base of the > VMA used for such mappings is random, but the mappings are created in > predictable places within the VMA and in sequential order. With 3, new > VMAs are created to fully randomize the mappings. > > Mappings created with mmap(NULL, ...) are randomized and mremap(..., > MREMAP_MAYMOVE) will move the mappings even if not necessary. The > locations of heap (memory allocated with brk()), stack and vdso are > also randomized. It seems that always moving the mappings in mremap() can expose bugs where the callers don't actually expect the mappings to move, even though MREMAP_MAYMOVE is specified (Debian libapt-pkg6.0): https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=980037 Perhaps this part should be a separate option to avoid tripping such bugs when compatibility is more important than improved ASLR and debugging. The option could be also used without randomize_va_space==3. How about something like sysctl.kernel.mremap_always_move, sysctl.vm.mremap_always_move or CONFIG_MREMAP_ALWAYS_MOVE? -Topi
diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst index e05e581af5cf..9ea250522077 100644 --- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -254,7 +254,7 @@ Spectre variant 2 left by the previous process will also be cleared. User programs should use address space randomization to make attacks - more difficult (Set /proc/sys/kernel/randomize_va_space = 1 or 2). + more difficult (Set /proc/sys/kernel/randomize_va_space = 1, 2 or 3). 3. A virtualized guest attacking the host ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -499,8 +499,8 @@ Spectre variant 2 more overhead and run slower. User programs should use address space randomization - (/proc/sys/kernel/randomize_va_space = 1 or 2) to make attacks more - difficult. + (/proc/sys/kernel/randomize_va_space = 1, 2 or 3) to make attacks + more difficult. 3. VM mitigation ^^^^^^^^^^^^^^^^ diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index d4b32cc32bb7..5de63c8eefc8 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -1060,6 +1060,29 @@ that support this feature. Systems with ancient and/or broken binaries should be configured with ``CONFIG_COMPAT_BRK`` enabled, which excludes the heap from process address space randomization. + +3 Additionally enable full randomization of memory mappings. With 2, + the base of the VMA used for such mappings may be random, but the + mappings are created in predictable places within the VMA and in + sequential order. With 3, new VMAs are created to fully randomize + the mappings. + + Mappings created with mmap(NULL, ...) are randomized and + mremap(..., MREMAP_MAYMOVE) will move the mappings even if not + necessary. The locations of heap (memory allocated with brk()), + stack and vdso are also randomized. + + On 32 bit systems this may cause problems due to increased VM + fragmentation if the address space gets crowded, so this flag is + ignored for 32 bit compatibility personalities. + + On all systems, it will reduce performance and increase memory and + cache usage due to less efficient use of page tables and inability + to merge adjacent VMAs with compatible attributes. On x86_64 with + 5 level page tables, in the worst case, additional page table + entries of up to 4 pages are created for each mapping, so with + small mappings there's considerable penalty. + == =========================================================================== diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index fbf26e0f7a6a..d95a8f1e101c 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -266,7 +266,7 @@ config ARCH_MMAP_RND_BITS_MIN default 8 config ARCH_MMAP_RND_BITS_MAX - default 32 if 64BIT + default 35 if 64BIT default 16 config ARCH_MMAP_RND_COMPAT_BITS_MIN diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c index 9185cb1d13b9..5a30e53cdc1d 100644 --- a/arch/x86/entry/vdso/vma.c +++ b/arch/x86/entry/vdso/vma.c @@ -361,7 +361,12 @@ static unsigned long vdso_addr(unsigned long start, unsigned len) static int map_vdso_randomized(const struct vdso_image *image) { - unsigned long addr = vdso_addr(current->mm->start_stack, image->size-image->sym_vvar_start); + unsigned long addr; + + if (can_randomize_full()) + addr = 0; /* let get_unmapped_area() pick the address */ + else + addr = vdso_addr(current->mm->start_stack, image->size-image->sym_vvar_start); return map_vdso(image, addr); } diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 145a7ac0c19a..bdfd457adfa8 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -905,7 +905,10 @@ unsigned long arch_align_stack(unsigned long sp) unsigned long arch_randomize_brk(struct mm_struct *mm) { - return randomize_page(mm->brk, 0x02000000); + if (can_randomize_full()) + return arch_mmap_rnd(); + else + return randomize_page(mm->brk, 0x02000000); } /* diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c index c90c20904a60..31b0e4e1a4c1 100644 --- a/arch/x86/mm/mmap.c +++ b/arch/x86/mm/mmap.c @@ -21,6 +21,7 @@ #include <linux/elf-randomize.h> #include <asm/elf.h> #include <asm/io.h> +#include <linux/security.h> #include "physaddr.h" @@ -122,6 +123,8 @@ static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base, *legacy_base = mmap_legacy_base(random_factor, task_size); if (mmap_is_legacy()) *base = *legacy_base; + else if (can_randomize_full()) + *base = mmap_min_addr; else *base = mmap_base(random_factor, task_size, rlim_stack); } diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index fa50e8936f5f..8d681e06cfcd 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1108,7 +1108,12 @@ static int load_elf_binary(struct linux_binprm *bprm) * without MAP_FIXED). */ if (interpreter) { - load_bias = ELF_ET_DYN_BASE; + if (can_randomize_full()) + /* more space for randomization */ + load_bias = mmap_min_addr; + else + load_bias = ELF_ET_DYN_BASE; + if (current->flags & PF_RANDOMIZE) load_bias += arch_mmap_rnd(); alignment = maximum_alignment(elf_phdata, elf_ex->e_phnum); @@ -1277,6 +1282,13 @@ static int load_elf_binary(struct linux_binprm *bprm) } mm->brk = mm->start_brk = arch_randomize_brk(mm); + if (can_randomize_full()) { + unsigned long random_offset = get_random_int() & ~PAGE_MASK & ~0xf; + mm->brk += random_offset; + retval = vm_brk_flags(mm->start_brk, random_offset, 0); + if (retval) + goto out; + } #ifdef compat_brk_randomized current->brk_randomized = 1; #endif diff --git a/include/linux/mm.h b/include/linux/mm.h index db6ae4d3fb4e..2e8c088f83e3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -31,6 +31,7 @@ #include <linux/sizes.h> #include <linux/sched.h> #include <linux/pgtable.h> +#include <linux/compat.h> struct mempolicy; struct anon_vma; @@ -2985,8 +2986,17 @@ void drop_slab_node(int nid); #ifndef CONFIG_MMU #define randomize_va_space 0 +static inline bool can_randomize_full(void) { return false; } #else extern int randomize_va_space; +static inline bool can_randomize_full(void) +{ + /* Don't randomize 32 bit applications */ + return !(current->personality & (ADDR_NO_RANDOMIZE | ADDR_COMPAT_LAYOUT + | ADDR_LIMIT_32BIT | ADDR_LIMIT_3GB)) + && !(IS_ENABLED(CONFIG_64BIT) && in_32bit_syscall()) + && randomize_va_space == 3; +} #endif const char * arch_vma_name(struct vm_area_struct *vma); diff --git a/init/Kconfig b/init/Kconfig index 0872a5a2e759..3b8982262b06 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1873,7 +1873,7 @@ config COMPAT_BRK also breaks ancient binaries (including anything libc5 based). This option changes the bootup default to heap randomization disabled, and can be overridden at runtime by setting - /proc/sys/kernel/randomize_va_space to 2. + /proc/sys/kernel/randomize_va_space to 2 or 3. On non-ancient distros (post-2000 ones) N is usually a safe choice. diff --git a/mm/mmap.c b/mm/mmap.c index 5c8b4485860d..a55f32981946 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -47,6 +47,7 @@ #include <linux/pkeys.h> #include <linux/oom.h> #include <linux/sched/mm.h> +#include <linux/elf-randomize.h> #include <linux/uaccess.h> #include <asm/cacheflush.h> @@ -73,6 +74,8 @@ const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX; int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS; #endif +#define MAX_RANDOM_MMAP_RETRIES 5 + static bool ignore_rlimit_data; core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644); @@ -206,7 +209,7 @@ SYSCALL_DEFINE1(brk, unsigned long, brk) #ifdef CONFIG_COMPAT_BRK /* * CONFIG_COMPAT_BRK can still be overridden by setting - * randomize_va_space to 2, which will still cause mm->start_brk + * randomize_va_space to >= 2, which will still cause mm->start_brk * to be arbitrarily shifted */ if (current->brk_randomized) @@ -2281,10 +2284,30 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, get_area = shmem_get_unmapped_area; } + /* Pick a random address even outside current VMAs? */ + if (!addr && can_randomize_full()) { + int i; + unsigned long new_addr; + + /* Try a few times to find a free area */ + for (i = 0; i < MAX_RANDOM_MMAP_RETRIES; i++) { + new_addr = arch_mmap_rnd(); + + new_addr = get_area(file, new_addr, len, pgoff, + flags | MAP_FIXED_NOREPLACE); + if (!IS_ERR_VALUE(new_addr)) { + addr = new_addr; + goto found; + } + } + /* failed, retry with original addr */ + } + addr = get_area(file, addr, len, pgoff, flags); if (IS_ERR_VALUE(addr)) return addr; + found: if (addr > TASK_SIZE - len) return -ENOMEM; if (offset_in_page(addr)) diff --git a/mm/mremap.c b/mm/mremap.c index 138abbae4f75..9cdb680318e8 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -665,6 +665,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, unsigned long charged = 0; bool locked = false; bool downgraded = false; + bool randomize = false; struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX; LIST_HEAD(uf_unmap_early); LIST_HEAD(uf_unmap); @@ -720,6 +721,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, goto out; } + randomize = (flags & MREMAP_MAYMOVE) && can_randomize_full(); /* * Always allow a shrinking remap: that just unmaps * the unnecessary pages.. @@ -730,7 +732,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, int retval; retval = __do_munmap(mm, addr+new_len, old_len - new_len, - &uf_unmap, true); + &uf_unmap, !randomize); if (retval < 0 && old_len != new_len) { ret = retval; goto out; @@ -738,6 +740,16 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, } else if (retval == 1) downgraded = true; ret = addr; + + /* + * Caller is happy with a new address, so let's move + * even if not necessary + */ + if (randomize) + ret = mremap_to(addr, new_len, 0, new_len, + &locked, flags, &uf, &uf_unmap_early, + &uf_unmap); + goto out; } @@ -751,8 +763,10 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, } /* old_len exactly to the end of the area.. + * But when randomizing, don't just expand the mapping if + * caller is happy with a moved and resized mapping */ - if (old_len == vma->vm_end - addr) { + if (old_len == vma->vm_end - addr && !randomize) { /* can we just expand the current mapping? */ if (vma_expandable(vma, new_len - old_len)) { int pages = (new_len - old_len) >> PAGE_SHIFT; diff --git a/mm/util.c b/mm/util.c index 4ddb6e186dd5..475d4eaa8ff1 100644 --- a/mm/util.c +++ b/mm/util.c @@ -320,6 +320,9 @@ unsigned long randomize_stack_top(unsigned long stack_top) unsigned long random_variable = 0; if (current->flags & PF_RANDOMIZE) { + if (can_randomize_full()) + return arch_mmap_rnd(); + random_variable = get_random_long(); random_variable &= STACK_RND_MASK; random_variable <<= PAGE_SHIFT; @@ -338,6 +341,9 @@ unsigned long arch_randomize_brk(struct mm_struct *mm) if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task()) return randomize_page(mm->brk, SZ_32M); + if (can_randomize_full()) + return arch_mmap_rnd(); + return randomize_page(mm->brk, SZ_1G); } @@ -412,7 +418,10 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) #elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT) void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) { - mm->mmap_base = TASK_UNMAPPED_BASE; + if (can_randomize_full()) + mm->mmap_base = mmap_min_addr; + else + mm->mmap_base = TASK_UNMAPPED_BASE; mm->get_unmapped_area = arch_get_unmapped_area; } #endif
Writing a new value of 3 to /proc/sys/kernel/randomize_va_space enables full randomization of memory mappings. With 2, the base of the VMA used for such mappings is random, but the mappings are created in predictable places within the VMA and in sequential order. With 3, new VMAs are created to fully randomize the mappings. Mappings created with mmap(NULL, ...) are randomized and mremap(..., MREMAP_MAYMOVE) will move the mappings even if not necessary. The locations of heap (memory allocated with brk()), stack and vdso are also randomized. On 32 bit systems this may cause problems due to increased VM fragmentation if the address space gets crowded, so this flag is ignored for 32 bit compatibility personalities. On all systems, it will reduce performance and increase memory and cache usage due to less efficient use of page tables and inability to merge adjacent VMAs with compatible attributes. On x86_64 with 5 level page tables, in the worst case, additional page table entries of up to 4 pages are created for each mapping, so with small mappings there's considerable penalty. By lowering the lowest address for mapping the main executable from 2/3 of the address space to sysctl.vm.mmap_min_addr, it's possible to use the full 35 bits available on x86_64 for ASLR. This is not usable without sysctl.kernel.randomize_va_space = 3. The method is to randomize the new address without considering VMAs. If the address fails checks because of overlap with the stack area (or in case of mremap(), overlap with the old mapping), the operation is retried a few times before falling back to old method. Kernel compile time was increased by 3% with 35 bits randomization instead of 28 and sysctl.kernel.randomize_va_space = 3 instead of 2. In another test involving X11 session with a browser with several tabs open, the memory reported in PageTables field in /proc/meminfo was increased from 67MB to 137MB, or 104% increase. In this example with sysctl.kernel.randomize_va_space = 2, main executable, heap allocated with brk(), locale-archive, libc, dynamic loader, some anonymous memory reserved with mmap(), stack and vdso are located in three groups and inside each group the mappings are close to each other: $ echo 2 > /proc/sys/kernel/randomize_va_space $ echo 28 > /proc/sys/vm/mmap_rnd_bits $ cat /proc/self/maps (only first line for each object shown for brevity) 55c6af2a6000-55c6af2a8000 r--p 00000000 fe:0c 1868624 /usr/bin/cat 55c6b0087000-55c6b00a8000 rw-p 00000000 00:00 0 [heap] 7fba5d2f9000-7fba5d85b000 r--p 00000000 fe:0c 2474005 /usr/lib/locale/locale-archive 7fba5d85b000-7fba5d880000 r--p 00000000 fe:0c 2402332 /usr/lib/x86_64-linux-gnu/libc-2.31.so 7fba5da1c000-7fba5da22000 rw-p 00000000 00:00 0 7fba5da2c000-7fba5da4e000 rw-p 00000000 00:00 0 7fba5da4e000-7fba5da4f000 r--p 00000000 fe:0c 2400754 /usr/lib/x86_64-linux-gnu/ld-2.31.so 7fba5da7a000-7fba5da7b000 rw-p 00000000 00:00 0 7ffd1bae5000-7ffd1bb06000 rw-p 00000000 00:00 0 [stack] 7ffd1bb3b000-7ffd1bb3f000 r--p 00000000 00:00 0 [vvar] 7ffd1bb3f000-7ffd1bb41000 r-xp 00000000 00:00 0 [vdso] The heap is also aligned to page boundary: $ cat brk.S .globl _start _start: movq $12, %rax movq $0, %rdi syscall movq $60, %rax syscall $ strace ./brk brk(NULL) = 0xd92000 exit(0) = ? With sysctl.kernel.randomize_va_space = 3, the segments are located at unrelated addresses and the order is random: $ echo 3 > /proc/sys/kernel/randomize_va_space $ echo 35 > /proc/sys/vm/mmap_rnd_bits $ cat /proc/self/maps (only first line for each object shown for brevity) 14872b64000-14872b65000 r--p 00000000 fe:0c 2400754 /usr/lib/x86_64-linux-gnu/ld-2.31.so f242fb53000-f242fb57000 r--p 00000000 00:00 0 [vvar] f242fb57000-f242fb59000 r-xp 00000000 00:00 0 [vdso] 19c43add2000-19c43adf4000 rw-p 00000000 00:00 0 1eec5609e000-1eec560a0000 r--p 00000000 fe:0c 1868624 /usr/bin/cat 2760e70ad000-2760e70ae000 rw-p 00000000 00:00 0 37c0c5728000-37c0c572a000 rw-p 00000000 00:00 0 3a6175611000-3a6175632000 rw-p 00000000 00:00 0 [stack] 55159e8c4000-55159e8e9000 r--p 00000000 fe:0c 2402332 /usr/lib/x86_64-linux-gnu/libc-2.31.so 76d786a2e000-76d786f90000 r--p 00000000 fe:0c 2474005 /usr/lib/locale/locale-archive 7e8f9a574000-7e8f9a595000 rw-p 00000000 00:00 0 [heap] Also low address bits of heap are randomized as was already done for stack: $ strace ./brk brk(NULL) = 0x15b9727a3aa0 exit(0) = ? CC: Andrew Morton <akpm@linux-foundation.org> CC: Jann Horn <jannh@google.com> CC: Kees Cook <keescook@chromium.org> CC: Matthew Wilcox <willy@infradead.org> CC: Mike Rapoport <rppt@kernel.org> CC: Linux API <linux-api@vger.kernel.org> Signed-off-by: Topi Miettinen <toiwoton@gmail.com> --- v2: also randomize mremap(..., MREMAP_MAYMOVE) v3: avoid stack area and retry in case of bad random address (Jann Horn), improve description in kernel.rst (Matthew Wilcox) v4: - use /proc/$pid/maps in the example (Mike Rapaport) - CCs (Andrew Morton) - only check randomize_va_space == 3 v5: randomize also vdso and stack v6: - randomize also heap - use 35 bits for ASLR on x86_64 - RFC due to temporarily disabling mremap() randomization v7: reimplement mremap() randomization v8: - randomize also lowest bits of heap - use MAP_FIXED_NOREPLACE to find a random but unused area v9: fix debugging and 32 bit apps (Steam) --- Documentation/admin-guide/hw-vuln/spectre.rst | 6 ++--- Documentation/admin-guide/sysctl/kernel.rst | 23 +++++++++++++++++ arch/x86/Kconfig | 2 +- arch/x86/entry/vdso/vma.c | 7 +++++- arch/x86/kernel/process.c | 5 +++- arch/x86/mm/mmap.c | 3 +++ fs/binfmt_elf.c | 14 ++++++++++- include/linux/mm.h | 10 ++++++++ init/Kconfig | 2 +- mm/mmap.c | 25 ++++++++++++++++++- mm/mremap.c | 18 +++++++++++-- mm/util.c | 11 +++++++- 12 files changed, 114 insertions(+), 12 deletions(-) base-commit: 2c85ebc57b3e1817b6ce1a6b703928e113a90442