[v5,1/9] riscv/kprobe: Prepare the skeleton to implement RISCV OPTPROBES feature

Commit Message

Xim Dec. 24, 2022, 11:43 a.m. UTC

From: Liao Chang <[e-mail]>

Prepare skeleton to implement optimized kprobe on RISCV, it is consist
of Makfile, Kconfig and some architecture specific files: kprobe.h and
opt.c opt.c include some macro, type definition and functions required
by kprobe framework, opt_trampoline.S provide a piece of assembly code
template used to construct the detour buffer as the target of long jump
instruction(s) for each optimzed kprobe.

Since the jump range of PC-relative instruction JAL is +/-2M, that is
too small to reach the detour buffer, hence the foudamental idea to
address OPTPROBES on RISCV is replace 'EBREAK' with 'AUIPC/JALR'. which
means it needs to clobber one more instruction beside the kprobe
instruction, furthermore, RISCV supports hybird RVI and RVC in single
kernel binary, so in theory a pair of 'AUIPC/JALR' is about to clobber
10 bytes(3 RVC and 1 RVI, 2 bytes is padding for alignment) at worst
case. The second hardsome problem is looking for one integer register as
the destination of 'AUIPC/JALR' without any side-effect.

Signed-off-by: Liao Chang <[e-mail]>
Co-developed-by: Chen Guokai <[e-mail]>
Signed-off-by: Chen Guokai <[e-mail]>
---
 arch/riscv/Kconfig                        |  1 +
 arch/riscv/include/asm/kprobes.h          | 32 ++++++++++++++
 arch/riscv/kernel/probes/Makefile         |  1 +
 arch/riscv/kernel/probes/opt.c            | 51 +++++++++++++++++++++++
 arch/riscv/kernel/probes/opt_trampoline.S | 12 ++++++
 5 files changed, 97 insertions(+)
 create mode 100644 arch/riscv/kernel/probes/opt.c
 create mode 100644 arch/riscv/kernel/probes/opt_trampoline.S

Comments

Björn Töpel Jan. 2, 2023, 6:03 p.m. UTC | #1

Chen Guokai <[e-mail]> writes:

> From: Liao Chang <[e-mail]>
>
> Prepare skeleton to implement optimized kprobe on RISCV, it is consist
> of Makfile, Kconfig and some architecture specific files: kprobe.h and
> opt.c opt.c include some macro, type definition and functions required
> by kprobe framework, opt_trampoline.S provide a piece of assembly code
> template used to construct the detour buffer as the target of long jump
> instruction(s) for each optimzed kprobe.

This is pretty much just reiterating what diff-stat says. Please try to
explain why a certain change is done, instead of what. What is already
in the patch.

> Since the jump range of PC-relative instruction JAL is +/-2M, that is
> too small to reach the detour buffer, hence the foudamental idea to
> address OPTPROBES on RISCV is replace 'EBREAK' with 'AUIPC/JALR'. which
> means it needs to clobber one more instruction beside the kprobe
> instruction, furthermore, RISCV supports hybird RVI and RVC in single
> kernel binary, so in theory a pair of 'AUIPC/JALR' is about to clobber
> 10 bytes(3 RVC and 1 RVI, 2 bytes is padding for alignment) at worst
> case. The second hardsome problem is looking for one integer register as
> the destination of 'AUIPC/JALR' without any side-effect.

There are a number of spelling errors, please use a spellchecker and if
you reference a file (e.g. Makefile), make sure it is correctly spelled
out.

The comments above applies to all the commit messages of this series.


Björn

Liao, Chang Jan. 4, 2023, 8:34 a.m. UTC | #2

在 2023/1/3 2:03, Björn Töpel 写道:
> Chen Guokai <[e-mail]> writes:
> 
>> From: Liao Chang <[e-mail]>
>>
>> Prepare skeleton to implement optimized kprobe on RISCV, it is consist
>> of Makfile, Kconfig and some architecture specific files: kprobe.h and
>> opt.c opt.c include some macro, type definition and functions required
>> by kprobe framework, opt_trampoline.S provide a piece of assembly code
>> template used to construct the detour buffer as the target of long jump
>> instruction(s) for each optimzed kprobe.
> 
> This is pretty much just reiterating what diff-stat says. Please try to
> explain why a certain change is done, instead of what. What is already
> in the patch.

Thanks for your suggestion, i will explain further in next revision.

> 
>> Since the jump range of PC-relative instruction JAL is +/-2M, that is
>> too small to reach the detour buffer, hence the foudamental idea to
>> address OPTPROBES on RISCV is replace 'EBREAK' with 'AUIPC/JALR'. which
>> means it needs to clobber one more instruction beside the kprobe
>> instruction, furthermore, RISCV supports hybird RVI and RVC in single
>> kernel binary, so in theory a pair of 'AUIPC/JALR' is about to clobber
>> 10 bytes(3 RVC and 1 RVI, 2 bytes is padding for alignment) at worst
>> case. The second hardsome problem is looking for one integer register as
>> the destination of 'AUIPC/JALR' without any side-effect.
> 
> There are a number of spelling errors, please use a spellchecker and if
> you reference a file (e.g. Makefile), make sure it is correctly spelled
> out.
> 
> The comments above applies to all the commit messages of this series.

Thanks for reviewing, i will correct these spelling errors.

> 
> 
> Björn

Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e2b656043abf..5fa3094d55bc 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -103,6 +103,7 @@  config RISCV
 	select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL
 	select HAVE_KRETPROBES if !XIP_KERNEL
 	select HAVE_RETHOOK if !XIP_KERNEL
+	select HAVE_OPTPROBES if !XIP_KERNEL
 	select HAVE_MOVE_PMD
 	select HAVE_MOVE_PUD
 	select HAVE_PCI
diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
index e7882ccb0fd4..e85130c9112f 100644
--- a/arch/riscv/include/asm/kprobes.h
+++ b/arch/riscv/include/asm/kprobes.h
@@ -41,5 +41,37 @@  int kprobe_fault_handler(struct pt_regs *regs, unsigned int trapnr);
 bool kprobe_breakpoint_handler(struct pt_regs *regs);
 bool kprobe_single_step_handler(struct pt_regs *regs);
 
+#ifdef CONFIG_OPTPROBES
+
+/* optinsn template addresses */
+extern __visible kprobe_opcode_t optprobe_template_entry[];
+extern __visible kprobe_opcode_t optprobe_template_end[];
+
+#define MAX_OPTINSN_SIZE				\
+	((unsigned long)optprobe_template_end -		\
+	 (unsigned long)optprobe_template_entry)
+
+/*
+ * For RVI and RVC hybird encoding kernel, althought long jump just needs
+ * 2 RVI instructions(AUIPC+JALR), optimized instructions is 10 bytes long
+ * at most to ensure no RVI would be truncated actually, so it means four
+ * combinations:
+ * - 2 RVI
+ * - 4 RVC
+ * - 2 RVC + 1 RVI
+ * - 3 RVC + 1 RVI (truncated, need padding)
+ */
+#define MAX_COPIED_INSN		4
+#define MAX_OPTIMIZED_LENGTH	10
+
+struct arch_optimized_insn {
+	kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
+	/* detour code buffer */
+	kprobe_opcode_t *insn;
+	unsigned long length;
+	int rd;
+};
+
+#endif /* CONFIG_OPTPROBES */
 #endif /* CONFIG_KPROBES */
 #endif /* _ASM_RISCV_KPROBES_H */
diff --git a/arch/riscv/kernel/probes/Makefile b/arch/riscv/kernel/probes/Makefile
index c40139e9ca47..3d837eb5f9be 100644
--- a/arch/riscv/kernel/probes/Makefile
+++ b/arch/riscv/kernel/probes/Makefile
@@ -3,4 +3,5 @@  obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o
 obj-$(CONFIG_RETHOOK)		+= rethook.o rethook_trampoline.o
 obj-$(CONFIG_KPROBES_ON_FTRACE)	+= ftrace.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o simulate-insn.o
+obj-$(CONFIG_OPTPROBES)		+= opt.o opt_trampoline.o
 CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)
diff --git a/arch/riscv/kernel/probes/opt.c b/arch/riscv/kernel/probes/opt.c
new file mode 100644
index 000000000000..56c8a227c857
--- /dev/null
+++ b/arch/riscv/kernel/probes/opt.c
@@ -0,0 +1,51 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Kernel Probes Jump Optimization (Optprobes)
+ *
+ * Copyright (C) Guokai Chen, 2022
+ * Author: Guokai Chen [e-mail]
+ */
+
+#define pr_fmt(fmt)	"optprobe: " fmt
+
+#include <linux/kprobes.h>
+#include <asm/kprobes.h>
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+	return 0;
+}
+
+int arch_check_optimized_kprobe(struct optimized_kprobe *op)
+{
+	return 0;
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
+				  struct kprobe *orig)
+{
+	return 0;
+}
+
+void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
+{
+}
+
+void arch_optimize_kprobes(struct list_head *oplist)
+{
+}
+
+void arch_unoptimize_kprobes(struct list_head *oplist,
+			     struct list_head *done_list)
+{
+}
+
+void arch_unoptimize_kprobe(struct optimized_kprobe *op)
+{
+}
+
+int arch_within_optimized_kprobe(struct optimized_kprobe *op,
+				 kprobe_opcode_t *addr)
+{
+	return 0;
+}
diff --git a/arch/riscv/kernel/probes/opt_trampoline.S b/arch/riscv/kernel/probes/opt_trampoline.S
new file mode 100644
index 000000000000..16160c4367ff
--- /dev/null
+++ b/arch/riscv/kernel/probes/opt_trampoline.S
@@ -0,0 +1,12 @@ 
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2022 Guokai Chen
+ */
+
+#include <linux/linkage.h>
+
+#incldue <asm/csr.h>
+#include <asm/asm-offsets.h>
+
+SYM_ENTRY(optprobe_template_entry, SYM_L_GLOBAL, SYM_A_NONE)
+SYM_ENTRY(optprobe_template_end, SYM_L_GLOBAL, SYM_A_NONE)