From: Kees Cook <keescook@chromium.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org,
"Gustavo A . R . Silva" <gustavoars@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] hardening: Default to INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO
Date: Tue, 14 Sep 2021 12:14:47 -0700 [thread overview]
Message-ID: <202109141214.630BB3A@keescook> (raw)
In-Reply-To: <CAKwvOdnrO7X8h-g9Pn8RmfJhqj2zn3HJwpQ0p2EONNtFF0w-uA@mail.gmail.com>
On Tue, Sep 14, 2021 at 11:53:38AM -0700, Nick Desaulniers wrote:
> 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:
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
next prev parent reply other threads:[~2021-09-14 19:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-14 10:28 [PATCH] hardening: Default to INIT_STACK_ALL_ZERO if CC_HAS_AUTO_VAR_INIT_ZERO Will Deacon
2021-09-14 15:58 ` Nathan Chancellor
2021-09-14 17:21 ` Kees Cook
2021-09-14 18:53 ` Nick Desaulniers
2021-09-14 19:09 ` Kees Cook
2021-09-14 19:14 ` Kees Cook [this message]
2021-09-14 19:22 ` Nick Desaulniers
2021-09-14 19:36 ` Nathan Chancellor
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