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Message-ID: <20191115141807.GE41572@lakrids.cambridge.arm.com>
Date: Fri, 15 Nov 2019 14:18:07 +0000
From: Mark Rutland <mark.rutland@....com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Will Deacon <will@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Dave Martin <Dave.Martin@....com>,
	Kees Cook <keescook@...omium.org>,
	Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Jann Horn <jannh@...gle.com>,
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	clang-built-linux@...glegroups.com,
	kernel-hardening@...ts.openwall.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 08/14] arm64: disable function graph tracing with SCS

On Tue, Nov 05, 2019 at 03:56:02PM -0800, Sami Tolvanen wrote:
> The graph tracer hooks returns by modifying frame records on the
> (regular) stack, but with SCS the return address is taken from the
> shadow stack, and the value in the frame record has no effect. As we
> don't currently have a mechanism to determine the corresponding slot
> on the shadow stack (and to pass this through the ftrace
> infrastructure), for now let's disable the graph tracer when SCS is
> enabled.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Mark Rutland <mark.rutland@....com>

Mark.

> ---
>  arch/arm64/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 3f047afb982c..8cda176dad9a 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.rc1.363.gb1bccd3e3d-goog
> 

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