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Message-ID: <202001281449.FB1671805E@keescook>
Date: Tue, 28 Jan 2020 14:50:00 -0800
From: Kees Cook <keescook@...omium.org>
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>,
Mark Rutland <mark.rutland@....com>, james.morse@....com,
Dave Martin <Dave.Martin@....com>,
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 v7 04/11] scs: disable when function graph tracing is
enabled
On Tue, Jan 28, 2020 at 10:49:27AM -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 SCS when the graph tracer is
> enabled.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> arch/Kconfig | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 1b16aa9a3fe5..0d746373c52e 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -530,6 +530,7 @@ config ARCH_SUPPORTS_SHADOW_CALL_STACK
>
> config SHADOW_CALL_STACK
> bool "Clang Shadow Call Stack"
> + depends on !FUNCTION_GRAPH_TRACER
> depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
> help
> This option enables Clang's Shadow Call Stack, which uses a
> --
> 2.25.0.341.g760bfbb309-goog
>
--
Kees Cook
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