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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id m21sm2406530pjl.14.2021.09.14.13.02.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Sep 2021 13:02:06 -0700 (PDT) From: Kees Cook To: Kees Cook Cc: Greg Kroah-Hartman , Masahiro Yamada , llvm@lists.linux.dev, Will Deacon , Nick Desaulniers , Nathan Chancellor , "Gustavo A. R. Silva" , Michal Marek , James Morris , "Serge E. Hallyn" , linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-security-module@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2] hardening: Avoid harmless Clang option under CONFIG_INIT_STACK_ALL_ZERO Date: Tue, 14 Sep 2021 13:02:03 -0700 Message-Id: <20210914200203.1667751-1-keescook@chromium.org> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2977; h=from:subject; bh=imXvSq9i08/jXla4+sBmsEoHRgxDVq0c/pR4Y+Src2Y=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBhQP+6KIBv7ADhwLtBfRJcxajHiIjU9syPZkgPPvze 7pK8/OSJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCYUD/ugAKCRCJcvTf3G3AJmttD/ 4mVU7Uy78lGKS9GG4/AATbbI2r+H4dlMvkCBdPoS9u0ZZWy9ANO/hgX4YAbWMHyJlcwuYaEF0qlNXY FH+7dggnZaFS02i3ZFJLPcdDZPEBZnFO87uTxXL9lDha35X9mC7epPNTP4noj25bU5erE5pbxyxPDu DqImezS/gxrMsa1DPkvzKshSTEOM/LfO9VmN9wucjUMzlEYZzsToT+DbvdczK0B5RgoCSY787J5FYu 6P+N5A3SeT4ob22KoyAGNYGhXjELxTAPqnvXbj0CEkRh1WKNc8Knz/R9mk3FCx0qMkCRx5UxqYXMc2 E46IBRhrauS2lc2V0BQ9Ucip2broVQVj/A5jWAt7zd3JubGP14NTreyt9tV3Ry21uOrZfpipH/Txh5 plKgkla9cKh4yOR6PXD6wmEihq0pkOrOg3HSkWLtH2/dknakAYmN863uoCRPbe86Y2PMyM9uy1EU7V 9pS8Hz+GnxJLTX6HMJvQZvCyfQ/9Nj996X3+9iXDguWxM1fqrw9vwr/qdP1GO0jMKb/CqdAUNM1Xge 2tzx3f9Ds6ue6YV6t28roXbHEyYyTwzggRYDpWyj6pbN3NknET2P0o8TNtnCBFLDYyQKwc9YstZ02m vuyuoahu6RDM2jnuT5Khd3rtsnEBEbQW7Wp952MN5xrEpYIsZ2Os14rEiVNw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org Currently under Clang, CC_HAS_AUTO_VAR_INIT_ZERO requires an extra -enable flag compared to CC_HAS_AUTO_VAR_INIT_PATTERN. GCC does not, and will happily ignore the Clang-specific flag. However, its presence on the command-line is both cumbersome and confusing. Due to GCC's tolerant behavior, though, we can continue to use a single Kconfig cc-option test for the feature on both compilers, but then drop the Clang-specific option in the Makefile. Cc: Greg Kroah-Hartman Cc: Masahiro Yamada Cc: llvm@lists.linux.dev Fixes: dcb7c0b9461c ("hardening: Clarify Kconfig text for auto-var-init") Suggested-by: Will Deacon Link: https://lore.kernel.org/lkml/20210914102837.6172-1-will@kernel.org/ Reviewed-by: Nick Desaulniers Reviewed-by: Nathan Chancellor Signed-off-by: Kees Cook Acked-by: Will Deacon --- Makefile | 6 +++--- security/Kconfig.hardening | 5 ++++- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/Makefile b/Makefile index 34a0afc3a8eb..72d165ffabdb 100644 --- a/Makefile +++ b/Makefile @@ -831,12 +831,12 @@ endif # Initialize all stack variables with a zero value. ifdef CONFIG_INIT_STACK_ALL_ZERO -# Future support for zero initialization is still being debated, see -# https://bugs.llvm.org/show_bug.cgi?id=45497. These flags are subject to being -# renamed or dropped. KBUILD_CFLAGS += -ftrivial-auto-var-init=zero +ifdef CONFIG_CC_IS_CLANG +# https://bugs.llvm.org/show_bug.cgi?id=45497 KBUILD_CFLAGS += -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang endif +endif # While VLAs have been removed, GCC produces unreachable stack probes # for the randomize_kstack_offset feature. Disable it for all compilers. diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index 90cbaff86e13..ded17b8abce2 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -23,13 +23,16 @@ config CC_HAS_AUTO_VAR_INIT_PATTERN def_bool $(cc-option,-ftrivial-auto-var-init=pattern) config CC_HAS_AUTO_VAR_INIT_ZERO + # GCC ignores the -enable flag, so we can test for the feature with + # a single invocation using the flag, but drop it as appropriate in + # the Makefile, depending on the presence of Clang. def_bool $(cc-option,-ftrivial-auto-var-init=zero -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang) choice prompt "Initialize kernel stack variables at function entry" default GCC_PLUGIN_STRUCTLEAK_BYREF_ALL if COMPILE_TEST && GCC_PLUGINS default INIT_STACK_ALL_PATTERN if COMPILE_TEST && CC_HAS_AUTO_VAR_INIT_PATTERN - default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_PATTERN + default INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO default INIT_STACK_NONE help This option enables initialization of stack variables at