linux-kernel - Re: [PATCH v3 6/9] arm64: Recover kretprobe modified return address in stacktrace

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Date:   Thu, 21 Oct 2021 11:15:12 +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 v3 6/9] arm64: Recover kretprobe modified return address
 in stacktrace

On Thu, Oct 21, 2021 at 09:55:09AM +0900, Masami Hiramatsu wrote:
> Since the kretprobe replaces the function return address with
> the kretprobe_trampoline on the stack, stack unwinder shows it
> instead of the correct return address.
> 
> This checks whether the next return address is the
> __kretprobe_trampoline(), and if so, try to find the correct
> return address from the kretprobe instance list. For this purpose
> this adds 'kr_cur' loop cursor to memorize the current kretprobe
> instance.
> 
> With this fix, now arm64 can enable
> CONFIG_ARCH_CORRECT_STACKTRACE_ON_KRETPROBE, and pass the
> kprobe self tests.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  Changes in v2:
>   - Add comment for kr_cur.
>   - Make the kretprobe related code depends on CONFIG_KRETPROBES.
>   - Initialize "kr_cur" directly in start_backtrace() instead
>     of clearing "frame" data structure by memset().
> ---
>  arch/arm64/Kconfig                  |    1 +
>  arch/arm64/include/asm/stacktrace.h |    4 ++++
>  arch/arm64/kernel/stacktrace.c      |    7 +++++++
>  3 files changed, 12 insertions(+)

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

I'm not sure how you're planning to merge this, so please let me know if
you want me to queue any of the arm64 bits.

Will