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Date:   Thu, 31 Oct 2019 20:58:00 -0700
From:   Kees Cook <keescook@chromium.org>
To:     samitolvanen@google.com
Cc:     Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Dave Martin <Dave.Martin@arm.com>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Jann Horn <jannh@google.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        clang-built-linux@googlegroups.com,
        kernel-hardening@lists.openwall.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 11/17] arm64: disable function graph tracing with SCS
Message-ID: <201910312056.E3315F0F@keescook>
References: <20191018161033.261971-1-samitolvanen@google.com>
 <20191031164637.48901-1-samitolvanen@google.com>
 <20191031164637.48901-12-samitolvanen@google.com>
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On Thu, Oct 31, 2019 at 09:46:31AM -0700, samitolvanen@google.com wrote:
> With CONFIG_FUNCTION_GRAPH_TRACER, function return addresses are
> modified in ftrace_graph_caller and prepare_ftrace_return to redirect
> control flow to ftrace_return_to_handler. This is incompatible with
> SCS.

IIRC, the argument was to disable these on a per-arch basis instead of
doing it as a "depends on !SHADOW_CALL_STACK" in the top-level function
graph tracer Kconfig? (I'm just thinking ahead to doing this again for
other architectures, though, I guess, there is much more work than just
that for, say, x86.)

Regardless:

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees


> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  arch/arm64/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e7b57a8a5531..42867174920f 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -148,7 +148,7 @@ config ARM64
>  	select HAVE_FTRACE_MCOUNT_RECORD
>  	select HAVE_FUNCTION_TRACER
>  	select HAVE_FUNCTION_ERROR_INJECTION
> -	select HAVE_FUNCTION_GRAPH_TRACER
> +	select HAVE_FUNCTION_GRAPH_TRACER if !SHADOW_CALL_STACK
>  	select HAVE_GCC_PLUGINS
>  	select HAVE_HW_BREAKPOINT if PERF_EVENTS
>  	select HAVE_IRQ_TIME_ACCOUNTING
> -- 
> 2.24.0.rc0.303.g954a862665-goog
> 

-- 
Kees Cook