linux-kernel - Re: [PATCH -tip v3 05/11] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe

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Date:   Sat, 20 Mar 2021 21:16:16 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kuba@...nel.org, mingo@...hat.com,
        ast@...nel.org, tglx@...utronix.de, kernel-team@...com, yhs@...com,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-ia64@...r.kernel.org
Subject: Re: [PATCH -tip v3 05/11] x86/kprobes: Add UNWIND_HINT_FUNC on
 kretprobe_trampoline code

On Fri, 19 Mar 2021 21:22:39 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> From: Josh Poimboeuf <jpoimboe@...hat.com>
> 
> Add UNWIND_HINT_FUNC on kretporbe_trampoline code so that ORC
> information is generated on the kretprobe_trampoline correctly.
> 

Test bot also found a new warning for this.

> >> arch/x86/kernel/kprobes/core.o: warning: objtool: kretprobe_trampoline()+0x25: call without frame pointer save/setup

With CONFIG_FRAME_POINTER=y.

Of course this can be fixed with additional "push %bp; mov %sp, %bp" before calling
trampoline_handler. But actually we know that this function has a bit special
stack frame too. 

Can I recover STACK_FRAME_NON_STANDARD(kretprobe_trampoline) when CONFIG_FRAME_POINTER=y ?

Thank you,


> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  [MH] Add patch description.
> ---
>  arch/x86/include/asm/unwind_hints.h |    5 +++++
>  arch/x86/kernel/kprobes/core.c      |    3 ++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
> index 8e574c0afef8..8b33674288ea 100644
> --- a/arch/x86/include/asm/unwind_hints.h
> +++ b/arch/x86/include/asm/unwind_hints.h
> @@ -52,6 +52,11 @@
>  	UNWIND_HINT sp_reg=ORC_REG_SP sp_offset=8 type=UNWIND_HINT_TYPE_FUNC
>  .endm
>  
> +#else
> +
> +#define UNWIND_HINT_FUNC \
> +	UNWIND_HINT(ORC_REG_SP, 8, UNWIND_HINT_TYPE_FUNC, 0)
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_X86_UNWIND_HINTS_H */
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 427d648fffcd..b31058a152b6 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -772,6 +772,7 @@ asm(
>  	/* We don't bother saving the ss register */
>  #ifdef CONFIG_X86_64
>  	"	pushq %rsp\n"
> +	UNWIND_HINT_FUNC
>  	"	pushfq\n"
>  	SAVE_REGS_STRING
>  	"	movq %rsp, %rdi\n"
> @@ -782,6 +783,7 @@ asm(
>  	"	popfq\n"
>  #else
>  	"	pushl %esp\n"
> +	UNWIND_HINT_FUNC
>  	"	pushfl\n"
>  	SAVE_REGS_STRING
>  	"	movl %esp, %eax\n"
> @@ -795,7 +797,6 @@ asm(
>  	".size kretprobe_trampoline, .-kretprobe_trampoline\n"
>  );
>  NOKPROBE_SYMBOL(kretprobe_trampoline);
> -STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
>  
>  
>  /*
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>