linux-kernel - [tip: x86/build] x86/Kconfig: Fix CONFIG_CC_HAS_SANE_STACKPROTECTOR when cross compiling with clang

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Date:   Mon, 11 Jul 2022 07:04:41 -0000
From:   "tip-bot2 for Nathan Chancellor" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/build] x86/Kconfig: Fix CONFIG_CC_HAS_SANE_STACKPROTECTOR
 when cross compiling with clang

The following commit has been merged into the x86/build branch of tip:

Commit-ID:     1b8667812b3a1304f3db736ac4905d6ad77d721e
Gitweb:        https://git.kernel.org/tip/1b8667812b3a1304f3db736ac4905d6ad77d721e
Author:        Nathan Chancellor <nathan@...nel.org>
AuthorDate:    Fri, 17 Jun 2022 11:08:46 -07:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Mon, 11 Jul 2022 08:49:39 +02:00

x86/Kconfig: Fix CONFIG_CC_HAS_SANE_STACKPROTECTOR when cross compiling with clang

Chimera Linux notes that CONFIG_CC_HAS_SANE_STACKPROTECTOR cannot be
enabled when cross compiling an x86_64 kernel with clang, even though it
does work when natively compiling.

When building on aarch64:

  $ make -sj"$(nproc)" ARCH=x86_64 LLVM=1 defconfig

  $ grep STACKPROTECTOR .config

When building on x86_64:

  $ make -sj"$(nproc)" ARCH=x86_64 LLVM=1 defconfig

  $ grep STACKPROTECTOR .config
  CONFIG_CC_HAS_SANE_STACKPROTECTOR=y
  CONFIG_HAVE_STACKPROTECTOR=y
  CONFIG_STACKPROTECTOR=y
  CONFIG_STACKPROTECTOR_STRONG=y

When clang is invoked without a '--target' flag, code is generated for
the default target, which is usually the host (it is configurable via
cmake). As a result, the has-stack-protector scripts will generate code
for the default target but check for x86 specific segment registers,
which cannot succeed if the default target is not x86.

$(CLANG_FLAGS) contains an explicit '--target' flag so pass that
variable along to the has-stack-protector scripts so that the stack
protector can be enabled when cross compiling with clang. The 32-bit
stack protector cannot currently be enabled with clang, as it does not
support '-mstack-protector-guard-symbol', so this results in no
functional change for ARCH=i386 when cross compiling.

Signed-off-by: Nathan Chancellor <nathan@...nel.org>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Link: https://github.com/chimera-linux/cports/commit/0fb7e506d5f83fdf2104feb22cdac34934561226
Link: https://github.com/llvm/llvm-project/issues/48553
Link: https://lkml.kernel.org/r/20220617180845.2788442-1-nathan@kernel.org
---
 arch/x86/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index be0b95e..076adde 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -391,8 +391,8 @@ config PGTABLE_LEVELS

 config CC_HAS_SANE_STACKPROTECTOR
 	bool
-	default $(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC)) if 64BIT
-	default $(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC))
+	default $(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) $(CLANG_FLAGS)) if 64BIT
+	default $(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC) $(CLANG_FLAGS))
 	help
 	  We have to make sure stack protector is unconditionally disabled if
 	  the compiler produces broken code or if it does not let us control