linux-kernel - [PATCH v8 04/12] scs: disable when function graph tracing is enabled

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Message-Id: <20200219000817.195049-5-samitolvanen@google.com>
Date:   Tue, 18 Feb 2020 16:08:09 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     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
Cc:     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,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v8 04/12] scs: disable when function graph tracing is enabled

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>
---
 arch/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 66b34fd0df54..4102b8e0eea9 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -535,6 +535,7 @@ 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
-- 
2.25.0.265.gbab2e86ba0-goog