linux-kernel - [PATCH] arm64: disable -fsanitize=shadow-call-stack for big-endian

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Message-Id: <20200527134016.753354-1-arnd@arndb.de>
Date:   Wed, 27 May 2020 15:39:46 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH] arm64: disable -fsanitize=shadow-call-stack for big-endian

clang-11 and earlier do not support -fsanitize=shadow-call-stack
in combination with -mbig-endian, but the Kconfig check does not
pass the endianess flag, so building a big-endian kernel with
this fails at build time:

clang: error: unsupported option '-fsanitize=shadow-call-stack' for target 'aarch64_be-unknown-linux'

Change the Kconfig check to let Kconfig figure this out earlier
and prevent the broken configuration. I assume this is a bug
in clang that needs to be fixed, but we also have to work
around existing releases.

Fixes: 5287569a790d ("arm64: Implement Shadow Call Stack")
Link: https://bugs.llvm.org/show_bug.cgi?id=46076
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm64/Kconfig | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index a82441d6dc36..692e1575a6c8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1031,7 +1031,9 @@ config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 
 # Supported by clang >= 7.0
 config CC_HAVE_SHADOW_CALL_STACK
-	def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
+	bool
+	default $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18 -mbig-endian) if CPU_BIG_ENDIAN
+	default $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18 -mlittle-endian) if !CPU_BIG_ENDIAN
 
 config SECCOMP
 	bool "Enable seccomp to safely compute untrusted bytecode"
-- 
2.26.2