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Message-ID: <5581BE4C.8070604@linaro.org>
Date: Wed, 17 Jun 2015 14:37:00 -0400
From: David Long <dave.long@...aro.org>
To: William Cohen <wcohen@...hat.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-arm-kernel@...ts.infradead.org,
Russell King <linux@....linux.org.uk>
CC: sandeepa.s.prabhu@...il.com,
Steve Capper <steve.capper@...aro.org>,
"Jon Medhurst (Tixy)" <tixy@...aro.org>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
davem@...emloft.net, Mark Brown <broonie@...nel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/7] arm64: Add trampoline code for kretprobes
On 06/16/15 11:09, William Cohen wrote:
> On 06/15/2015 03:07 PM, David Long wrote:
>> From: William Cohen <wcohen@...hat.com>
>>
>> The trampoline code is used by kretprobes to capture a return from a probed
>> function. This is done by saving the registers, calling the handler, and
>> restoring the registers. The code then returns to the roginal saved caller
>
> s/roginal/original
>
Hopefully no one wants a v8 if it turns out only to be to fix this typo
in the commit description. I'll keep this in mind if a respin is needed
for other reasons.
>> return address. It is necessary to do this directly instead of using a
>> software breakpoint because the code used in processing that breakpoint
>> could itself be kprobe'd and cause a problematic reentry into the debug
>> exception handler.
>>
>> Signed-off-by: William Cohen <wcohen@...hat.com>
>> Signed-off-by: David A. Long <dave.long@...aro.org>
>> ---
>> arch/arm64/include/asm/kprobes.h | 1 +
>> arch/arm64/kernel/kprobes-arm64.h | 41 +++++++++++++++++++++++++++++++++++++++
>> arch/arm64/kernel/kprobes.c | 26 +++++++++++++++++++++++++
>> 3 files changed, 68 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
>> index af31c4d..d081f49 100644
>> --- a/arch/arm64/include/asm/kprobes.h
>> +++ b/arch/arm64/include/asm/kprobes.h
>> @@ -58,5 +58,6 @@ int kprobe_exceptions_notify(struct notifier_block *self,
>> unsigned long val, void *data);
>> int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr);
>> int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr);
>> +void kretprobe_trampoline(void);
>>
>> #endif /* _ARM_KPROBES_H */
>> diff --git a/arch/arm64/kernel/kprobes-arm64.h b/arch/arm64/kernel/kprobes-arm64.h
>> index ff8a55f..bdcfa62 100644
>> --- a/arch/arm64/kernel/kprobes-arm64.h
>> +++ b/arch/arm64/kernel/kprobes-arm64.h
>> @@ -27,4 +27,45 @@ extern kprobes_pstate_check_t * const kprobe_condition_checks[16];
>> enum kprobe_insn __kprobes
>> arm_kprobe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi);
>>
>> +#define SAVE_REGS_STRING\
>> + " stp x0, x1, [sp, #16 * 0]\n" \
>> + " stp x2, x3, [sp, #16 * 1]\n" \
>> + " stp x4, x5, [sp, #16 * 2]\n" \
>> + " stp x6, x7, [sp, #16 * 3]\n" \
>> + " stp x8, x9, [sp, #16 * 4]\n" \
>> + " stp x10, x11, [sp, #16 * 5]\n" \
>> + " stp x12, x13, [sp, #16 * 6]\n" \
>> + " stp x14, x15, [sp, #16 * 7]\n" \
>> + " stp x16, x17, [sp, #16 * 8]\n" \
>> + " stp x18, x19, [sp, #16 * 9]\n" \
>> + " stp x20, x21, [sp, #16 * 10]\n" \
>> + " stp x22, x23, [sp, #16 * 11]\n" \
>> + " stp x24, x25, [sp, #16 * 12]\n" \
>> + " stp x26, x27, [sp, #16 * 13]\n" \
>> + " stp x28, x29, [sp, #16 * 14]\n" \
>> + " str x30, [sp, #16 * 15]\n" \
>> + " mrs x0, nzcv\n" \
>> + " str x0, [sp, #8 * 33]\n"
>> +
>> +
>> +#define RESTORE_REGS_STRING\
>> + " ldr x0, [sp, #8 * 33]\n" \
>> + " msr nzcv, x0\n" \
>> + " ldp x0, x1, [sp, #16 * 0]\n" \
>> + " ldp x2, x3, [sp, #16 * 1]\n" \
>> + " ldp x4, x5, [sp, #16 * 2]\n" \
>> + " ldp x6, x7, [sp, #16 * 3]\n" \
>> + " ldp x8, x9, [sp, #16 * 4]\n" \
>> + " ldp x10, x11, [sp, #16 * 5]\n" \
>> + " ldp x12, x13, [sp, #16 * 6]\n" \
>> + " ldp x14, x15, [sp, #16 * 7]\n" \
>> + " ldp x16, x17, [sp, #16 * 8]\n" \
>> + " ldp x18, x19, [sp, #16 * 9]\n" \
>> + " ldp x20, x21, [sp, #16 * 10]\n" \
>> + " ldp x22, x23, [sp, #16 * 11]\n" \
>> + " ldp x24, x25, [sp, #16 * 12]\n" \
>> + " ldp x26, x27, [sp, #16 * 13]\n" \
>> + " ldp x28, x29, [sp, #16 * 14]\n" \
>> + " ldr x30, [sp, #16 * 15]\n"
>> +
>> #endif /* _ARM_KERNEL_KPROBES_ARM64_H */
>> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
>> index 6255814..570218c 100644
>> --- a/arch/arm64/kernel/kprobes.c
>> +++ b/arch/arm64/kernel/kprobes.c
>> @@ -560,6 +560,32 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>> return 0;
>> }
>>
>> +/*
>> + * When a retprobed function returns, this code saves registers and
>> + * calls trampoline_handler() runs, which calls the kretprobe's handler.
>> + */
>> +static void __used __kprobes kretprobe_trampoline_holder(void)
>> +{
>> + asm volatile (".global kretprobe_trampoline\n"
>> + "kretprobe_trampoline:\n"
>> + "sub sp, sp, %0\n"
>> + SAVE_REGS_STRING
>> + "mov x0, sp\n"
>> + "bl trampoline_probe_handler\n"
>> + /* Replace trampoline address in lr with actual
>> + orig_ret_addr return address. */
>> + "str x0, [sp, #16 * 15]\n"
>> + RESTORE_REGS_STRING
>> + "add sp, sp, %0\n"
>> + "ret\n"
>> + : : "I"(sizeof(struct pt_regs)) : "memory");
>> +}
>> +
>> +static void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
>> +{
>> + return (void *) 0;
>> +}
>> +
>> int __init arch_init_kprobes(void)
>> {
>> return 0;
>>
>
--
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