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Message-ID: <5486CAF0.5040906@huawei.com>
Date: Tue, 9 Dec 2014 18:12:00 +0800
From: Wang Nan <wangnan0@...wei.com>
To: Masami Hiramatsu <masami.hiramatsu.pt@...achi.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
On 2014/12/9 14:47, Masami Hiramatsu wrote:
> (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 :)
>
So what's your opinion about this series of patches? Do you think they can be merged
into upstream code already? Or do you think we should eliminate stop_machine() first?
> Thank you!
>
>
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