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SubjectRe: [PATCH] x86/kprobes: Set up frame pointer in kprobe trampoline
On Tue,  3 Oct 2017 08:51:43 -0500
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> Richard Weinberger saw an unwinder warning when running bcc's opensnoop:
>
> WARNING: kernel stack frame pointer at ffff99ef4076bea0 in opensnoop:2008 has bad value 0000000000000008
> unwind stack type:0 next_sp: (null) mask:0x2 graph_idx:0
> ...
> ffff99ef4076be88: ffff99ef4076bea0 (0xffff99ef4076bea0)
> ffff99ef4076be90: ffffffffac442721 (optimized_callback +0x81/0x90)
> ...
>
> A lockdep stack trace was initiated from inside a kprobe handler, when
> the unwinder noticed a bad frame pointer on the stack. The bad frame
> pointer is related to the fact that the kprobe optprobe trampoline
> doesn't save the frame pointer before calling into optimized_callback().

OK, this looks good to me :)

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks!

>
> Reported-and-tested-by: Richard Weinberger <richard@sigma-star.at>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> arch/x86/kernel/kprobes/common.h | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/common.h b/arch/x86/kernel/kprobes/common.h
> index e2c2a1970869..595b56b37d27 100644
> --- a/arch/x86/kernel/kprobes/common.h
> +++ b/arch/x86/kernel/kprobes/common.h
> @@ -3,6 +3,15 @@
>
> /* Kprobes and Optprobes common header */
>
> +#include <asm/asm.h>
> +
> +#ifdef CONFIG_FRAME_POINTER
> +# define SAVE_RBP_STRING " push %" _ASM_BP "\n" \
> + " mov %" _ASM_SP ", %" _ASM_BP "\n"
> +#else
> +# define SAVE_RBP_STRING " push %" _ASM_BP "\n"
> +#endif
> +
> #ifdef CONFIG_X86_64
> #define SAVE_REGS_STRING \
> /* Skip cs, ip, orig_ax. */ \
> @@ -17,7 +26,7 @@
> " pushq %r10\n" \
> " pushq %r11\n" \
> " pushq %rbx\n" \
> - " pushq %rbp\n" \
> + SAVE_RBP_STRING \
> " pushq %r12\n" \
> " pushq %r13\n" \
> " pushq %r14\n" \
> @@ -48,7 +57,7 @@
> " pushl %es\n" \
> " pushl %ds\n" \
> " pushl %eax\n" \
> - " pushl %ebp\n" \
> + SAVE_RBP_STRING \
> " pushl %edi\n" \
> " pushl %esi\n" \
> " pushl %edx\n" \
> --
> 2.13.6
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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