linux-kernel - Re: [PATCH 3/8] arm64: kprobes: Record frame pointer with kretprobe instance

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Date:   Wed, 13 Oct 2021 09:14:45 +0100
From:   Will Deacon <will@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Ananth N Mavinakayanahalli <ananth@...ux.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Sven Schnelle <svens@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/8] arm64: kprobes: Record frame pointer with kretprobe
 instance

On Fri, Oct 08, 2021 at 09:28:39PM +0900, Masami Hiramatsu wrote:
> Record the frame pointer instead of stack address with kretprobe
> instance as the identifier on the instance list.
> Since arm64 always enable CONFIG_FRAME_POINTER, we can use the
> actual frame pointer (x29).
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  arch/arm64/kernel/probes/kprobes.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index e7ad6da980e8..d9dfa82c1f18 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -401,14 +401,14 @@ int __init arch_populate_kprobe_blacklist(void)
>  
>  void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
>  {
> -	return (void *)kretprobe_trampoline_handler(regs, (void *)kernel_stack_pointer(regs));
> +	return (void *)kretprobe_trampoline_handler(regs, (void *)regs->regs[29]);
>  }
>  
>  void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
>  				      struct pt_regs *regs)
>  {
>  	ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
> -	ri->fp = (void *)kernel_stack_pointer(regs);
> +	ri->fp = (void *)regs->regs[29];
>  
>  	/* replace return addr (x30) with trampoline */
>  	regs->regs[30] = (long)&__kretprobe_trampoline;

Acked-by: Will Deacon <will@...nel.org>

Will