Re: [PATCH] hardening: Default to INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
From: Nick Desaulniers <ndesaulniers@google.com>
Date: 2021-09-14 19:22:43
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On Tue, Sep 14, 2021 at 12:14 PM Kees Cook [off-list ref] wrote:
On Tue, Sep 14, 2021 at 11:53:38AM -0700, Nick Desaulniers wrote:quoted
Rather than create 2 new kconfigs with 1 new invocation of the compiler via cc-option, how about just adding an `ifdef CONFIG_CC_IS_CLANG` guard around adding the obnoxious flag to `KBUILD_CFLAGS` in the top level Makefile?v2:
LGTM Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> I think the formal patch should have Will's Suggested-by on it.
quoted hunk ↗ jump to hunk
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 --Kees Cook
-- Thanks, ~Nick Desaulniers