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SubjectRe: [PATCH 03/15] x86/kprobes: Fix frame pointer annotations
On Wed, 05 Jun 2019 15:07:56 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> The kprobe trampolines have a FRAME_POINTER annotation that makes no
> sense. It marks the frame in the middle of pt_regs, at the place of
> saving BP.

commit ee213fc72fd67 introduced this code, and this is for unwinder which
uses frame pointer. I think current code stores the address of previous
(original context's) frame pointer into %rbp. So with that, if unwinder
tries to decode frame pointer, it can get the original %rbp value,
instead of &pt_regs from current %rbp.

>
> Change it to mark the pt_regs frame as per the ENCODE_FRAME_POINTER
> from the respective entry_*.S.
>

With this change, I think stack unwinder can not get the original %rbp
value. Peter, could you check the above commit?

Thank you,

> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> arch/x86/kernel/kprobes/common.h | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> --- a/arch/x86/kernel/kprobes/common.h
> +++ b/arch/x86/kernel/kprobes/common.h
> @@ -5,15 +5,10 @@
> /* 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
> +#include <asm/frame.h>
>
> #ifdef CONFIG_X86_64
> +
> #define SAVE_REGS_STRING \
> /* Skip cs, ip, orig_ax. */ \
> " subq $24, %rsp\n" \
> @@ -27,11 +22,13 @@
> " pushq %r10\n" \
> " pushq %r11\n" \
> " pushq %rbx\n" \
> - SAVE_RBP_STRING \
> + " pushq %rbp\n" \
> " pushq %r12\n" \
> " pushq %r13\n" \
> " pushq %r14\n" \
> - " pushq %r15\n"
> + " pushq %r15\n" \
> + ENCODE_FRAME_POINTER
> +
> #define RESTORE_REGS_STRING \
> " popq %r15\n" \
> " popq %r14\n" \
> @@ -51,19 +48,22 @@
> /* Skip orig_ax, ip, cs */ \
> " addq $24, %rsp\n"
> #else
> +
> #define SAVE_REGS_STRING \
> /* Skip cs, ip, orig_ax and gs. */ \
> - " subl $16, %esp\n" \
> + " subl $4*4, %esp\n" \
> " pushl %fs\n" \
> " pushl %es\n" \
> " pushl %ds\n" \
> " pushl %eax\n" \
> - SAVE_RBP_STRING \
> + " pushl %ebp\n" \
> " pushl %edi\n" \
> " pushl %esi\n" \
> " pushl %edx\n" \
> " pushl %ecx\n" \
> - " pushl %ebx\n"
> + " pushl %ebx\n" \
> + ENCODE_FRAME_POINTER
> +
> #define RESTORE_REGS_STRING \
> " popl %ebx\n" \
> " popl %ecx\n" \
>
>


--
Masami Hiramatsu <mhiramat@kernel.org>

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