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Message-ID: <54869B1C.6050401@hitachi.com>
Date: Tue, 09 Dec 2014 15:47:56 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Wang Nan <wangnan0@...wei.com>
Cc: tixy@...aro.org, linux@....linux.org.uk, lizefan@...wei.com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RESEND][PATCH v15 7/7] ARM: kprobes: enable OPTPROBES for ARM
32
(2014/12/08 23:09), Wang Nan wrote:
> This patch introduce kprobeopt for ARM 32.
>
> Limitations:
> - Currently only kernel compiled with ARM ISA is supported.
>
> - Offset between probe point and optinsn slot must not larger than
> 32MiB. Masami Hiramatsu suggests replacing 2 words, it will make
> things complex. Futher patch can make such optimization.
>
> Kprobe opt on ARM is relatively simpler than kprobe opt on x86 because
> ARM instruction is always 4 bytes aligned and 4 bytes long. This patch
> replace probed instruction by a 'b', branch to trampoline code and then
> calls optimized_callback(). optimized_callback() calls opt_pre_handler()
> to execute kprobe handler. It also emulate/simulate replaced instruction.
>
> When unregistering kprobe, the deferred manner of unoptimizer may leave
> branch instruction before optimizer is called. Different from x86_64,
> which only copy the probed insn after optprobe_template_end and
> reexecute them, this patch call singlestep to emulate/simulate the insn
> directly. Futher patch can optimize this behavior.
>
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Jon Medhurst (Tixy) <tixy@...aro.org>
> Cc: Russell King - ARM Linux <linux@....linux.org.uk>
> Cc: Will Deacon <will.deacon@....com>
> ---
> v1 -> v2:
> - Improvement: if replaced instruction is conditional, generate a
> conditional branch instruction for it;
> - Introduces RELATIVEJUMP_OPCODES due to ARM kprobe_opcode_t is 4
> bytes;
> - Removes size field in struct arch_optimized_insn;
> - Use arm_gen_branch() to generate branch instruction;
> - Remove all recover logic: ARM doesn't use tail buffer, no need
> recover replaced instructions like x86;
> - Remove incorrect CONFIG_THUMB checking;
> - can_optimize() always returns true if address is well aligned;
> - Improve optimized_callback: using opt_pre_handler();
> - Bugfix: correct range checking code and improve comments;
> - Fix commit message.
>
> v2 -> v3:
> - Rename RELATIVEJUMP_OPCODES to MAX_COPIED_INSNS;
> - Remove unneeded checking:
> arch_check_optimized_kprobe(), can_optimize();
> - Add missing flush_icache_range() in arch_prepare_optimized_kprobe();
> - Remove unneeded 'return;'.
>
> v3 -> v4:
> - Use __mem_to_opcode_arm() to translate copied_insn to ensure it
> works in big endian kernel;
> - Replace 'nop' placeholder in trampoline code template with
> '.long 0' to avoid confusion: reader may regard 'nop' as an
> instruction, but it is value in fact.
>
> v4 -> v5:
> - Don't optimize stack store operations.
> - Introduce prepared field to arch_optimized_insn to indicate whether
> it is prepared. Similar to size field with x86. See v1 -> v2.
>
> v5 -> v6:
> - Dynamically reserve stack according to instruction.
> - Rename: kprobes-opt.c -> kprobes-opt-arm.c.
> - Set op->optinsn.insn after all works are done.
>
> v6 -> v7:
> - Using checker to check stack consumption.
>
> v7 -> v8:
> - Small code adjustments.
>
> v8 -> v9:
> - Utilize original kprobe passed to arch_prepare_optimized_kprobe()
> to avoid copy ainsn twice.
> - A bug in arch_prepare_optimized_kprobe() is found and fixed.
>
> v9 -> v10:
> - Commit message improvements.
>
> v10 -> v11:
> - Move to arch/arm/probes/, insn.h is moved to arch/arm/include/asm.
> - Code cleanup.
> - Bugfix based on Tixy's test result:
> - Trampoline deal with ARM -> Thumb transision instructions and
> AEABI stack alignment requirement correctly.
> - Trampoline code buffer should start at 4 byte aligned address.
> We enforces it in this series by using macro to wrap 'code' var.
>
> v11 -> v12:
> - Remove trampoline code stack trick and use r4 to save original
> stack.
> - Remove trampoline code buffer alignment trick.
> - Names of files are changed.
>
> v12 -> v13:
> - Assume stack always aligned by 4-bytes in any case.
> - Comments update.
>
> v13 -> v14:
> - Use stop_machine to wrap arch_optimize_kprobes to avoid a racing.
>
> v14 -> v15:
> - In v14, stop_machine() wraps a coarse-grained piece of code which
> makes things complex than it should be. In this version,
> kprobes_remove_breakpoint() is extracted, core.c and opt-arm.c use it
> to replace breakpoint to valid instruction. stop_machine() used inside
> in kprobes_remove_breakpoint().
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/{kernel => include/asm}/insn.h | 0
> arch/arm/include/asm/kprobes.h | 29 +++
> arch/arm/kernel/Makefile | 2 +-
> arch/arm/kernel/ftrace.c | 3 +-
> arch/arm/kernel/jump_label.c | 3 +-
> arch/arm/probes/kprobes/Makefile | 1 +
> arch/arm/probes/kprobes/core.c | 26 ++-
> arch/arm/probes/kprobes/core.h | 2 +
> arch/arm/probes/kprobes/opt-arm.c | 317 ++++++++++++++++++++++++++++++++
> 10 files changed, 372 insertions(+), 12 deletions(-)
> rename arch/arm/{kernel => include/asm}/insn.h (100%)
> create mode 100644 arch/arm/probes/kprobes/opt-arm.c
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 89c4b5c..2471240 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -59,6 +59,7 @@ config ARM
> select HAVE_MEMBLOCK
> select HAVE_MOD_ARCH_SPECIFIC if ARM_UNWIND
> select HAVE_OPROFILE if (HAVE_PERF_EVENTS)
> + select HAVE_OPTPROBES if !THUMB2_KERNEL
> select HAVE_PERF_EVENTS
> select HAVE_PERF_REGS
> select HAVE_PERF_USER_STACK_DUMP
> diff --git a/arch/arm/kernel/insn.h b/arch/arm/include/asm/insn.h
> similarity index 100%
> rename from arch/arm/kernel/insn.h
> rename to arch/arm/include/asm/insn.h
> diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
> index 56f9ac6..50ff3bc 100644
> --- a/arch/arm/include/asm/kprobes.h
> +++ b/arch/arm/include/asm/kprobes.h
> @@ -50,5 +50,34 @@ int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
> int kprobe_exceptions_notify(struct notifier_block *self,
> unsigned long val, void *data);
>
> +/* optinsn template addresses */
> +extern __visible kprobe_opcode_t optprobe_template_entry;
> +extern __visible kprobe_opcode_t optprobe_template_val;
> +extern __visible kprobe_opcode_t optprobe_template_call;
> +extern __visible kprobe_opcode_t optprobe_template_end;
> +extern __visible kprobe_opcode_t optprobe_template_sub_sp;
> +extern __visible kprobe_opcode_t optprobe_template_add_sp;
> +
> +#define MAX_OPTIMIZED_LENGTH 4
> +#define MAX_OPTINSN_SIZE \
> + ((unsigned long)&optprobe_template_end - \
> + (unsigned long)&optprobe_template_entry)
> +#define RELATIVEJUMP_SIZE 4
> +
> +struct arch_optimized_insn {
> + /*
> + * copy of the original instructions.
> + * Different from x86, ARM kprobe_opcode_t is u32.
> + */
> +#define MAX_COPIED_INSN DIV_ROUND_UP(RELATIVEJUMP_SIZE, sizeof(kprobe_opcode_t))
> + kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
> + /* detour code buffer */
> + kprobe_opcode_t *insn;
> + /*
> + * We always copy one instruction on ARM,
> + * so size will always be 4, and unlike x86, there is no
> + * need for a size field.
> + */
> +};
>
> #endif /* _ARM_KPROBES_H */
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index 40d3e00..1d0f4e7 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -52,7 +52,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o insn.o
> obj-$(CONFIG_JUMP_LABEL) += jump_label.o insn.o patch.o
> obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o
> # Main staffs in KPROBES are in arch/arm/probes/ .
> -obj-$(CONFIG_KPROBES) += patch.o
> +obj-$(CONFIG_KPROBES) += patch.o insn.o
> obj-$(CONFIG_OABI_COMPAT) += sys_oabi-compat.o
> obj-$(CONFIG_ARM_THUMBEE) += thumbee.o
> obj-$(CONFIG_KGDB) += kgdb.o
> diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
> index af9a8a9..ec7e332 100644
> --- a/arch/arm/kernel/ftrace.c
> +++ b/arch/arm/kernel/ftrace.c
> @@ -19,8 +19,7 @@
> #include <asm/cacheflush.h>
> #include <asm/opcodes.h>
> #include <asm/ftrace.h>
> -
> -#include "insn.h"
> +#include <asm/insn.h>
>
> #ifdef CONFIG_THUMB2_KERNEL
> #define NOP 0xf85deb04 /* pop.w {lr} */
> diff --git a/arch/arm/kernel/jump_label.c b/arch/arm/kernel/jump_label.c
> index c6c73ed..35a8fbb 100644
> --- a/arch/arm/kernel/jump_label.c
> +++ b/arch/arm/kernel/jump_label.c
> @@ -1,8 +1,7 @@
> #include <linux/kernel.h>
> #include <linux/jump_label.h>
> #include <asm/patch.h>
> -
> -#include "insn.h"
> +#include <asm/insn.h>
>
> #ifdef HAVE_JUMP_LABEL
>
> diff --git a/arch/arm/probes/kprobes/Makefile b/arch/arm/probes/kprobes/Makefile
> index bc8d504..76a36bf 100644
> --- a/arch/arm/probes/kprobes/Makefile
> +++ b/arch/arm/probes/kprobes/Makefile
> @@ -7,5 +7,6 @@ obj-$(CONFIG_KPROBES) += actions-thumb.o checkers-thumb.o
> test-kprobes-objs += test-thumb.o
> else
> obj-$(CONFIG_KPROBES) += actions-arm.o checkers-arm.o
> +obj-$(CONFIG_OPTPROBES) += opt-arm.o
> test-kprobes-objs += test-arm.o
> endif
> diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> index 3a58db4..a4ec240 100644
> --- a/arch/arm/probes/kprobes/core.c
> +++ b/arch/arm/probes/kprobes/core.c
> @@ -163,19 +163,31 @@ void __kprobes arch_arm_kprobe(struct kprobe *p)
> * memory. It is also needed to atomically set the two half-words of a 32-bit
> * Thumb breakpoint.
> */
> -int __kprobes __arch_disarm_kprobe(void *p)
> -{
> - struct kprobe *kp = p;
> - void *addr = (void *)((uintptr_t)kp->addr & ~1);
> -
> - __patch_text(addr, kp->opcode);
> +struct patch {
> + void *addr;
> + unsigned int insn;
> +};
>
> +static int __kprobes_remove_breakpoint(void *data)
> +{
> + struct patch *p = data;
> + __patch_text(p->addr, p->insn);
> return 0;
> }
>
> +void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
> +{
> + struct patch p = {
> + .addr = addr,
> + .insn = insn,
> + };
> + stop_machine(__kprobes_remove_breakpoint, &p, cpu_online_mask);
> +}
Hmm, I think finally we should fix patch_text() in patch.c to forcibly use stop_machine
by adding "bool stop" parameter, instead of introducing new another patch_text()
implementation, because we'd better avoid two private "patch" data structures.
Maybe someday we can find another better solution for self modifying.
(I actually doesn't like stop_machine() which disturbs real-time processing)
The other parts look good to me :)
Thank you!
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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