[PATCH] 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.
Link: https://github.com/chimera-linux/cports/commit/0fb7e506d5f83fdf2104feb22cdac... Link: https://github.com/llvm/llvm-project/issues/48553 Signed-off-by: Nathan Chancellor nathan@kernel.org ---
Fixes: 2a61f4747eea ("stack-protector: test compiler capability in Kconfig and drop AUTO mode")
might be appropriate; I am conflicted on fixes tags for problems that that arise due to use cases that were not considered at the time of a change, as it feels wrong to blame the commit for not looking far enough into the future where it might be common for people to have workstations running another architecture other than x86_64.
Chimera appears to use a 5.15 kernel so a
Cc: stable@vger.kernel.org
might be nice but some maintainers are picky about that so I leave it up to you all.
arch/x86/Kconfig | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index be0b95e51df6..076adde7ead9 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
base-commit: b13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3
Gentle ping for review.
On Fri, Jun 17, 2022 at 11:08:46AM -0700, Nathan Chancellor wrote:
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.
Link: https://github.com/chimera-linux/cports/commit/0fb7e506d5f83fdf2104feb22cdac... Link: https://github.com/llvm/llvm-project/issues/48553 Signed-off-by: Nathan Chancellor nathan@kernel.org
Fixes: 2a61f4747eea ("stack-protector: test compiler capability in Kconfig and drop AUTO mode")
might be appropriate; I am conflicted on fixes tags for problems that that arise due to use cases that were not considered at the time of a change, as it feels wrong to blame the commit for not looking far enough into the future where it might be common for people to have workstations running another architecture other than x86_64.
Chimera appears to use a 5.15 kernel so a
Cc: stable@vger.kernel.org
might be nice but some maintainers are picky about that so I leave it up to you all.
arch/x86/Kconfig | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index be0b95e51df6..076adde7ead9 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) $(CLANG_FLAGS)) help We have to make sure stack protector is unconditionally disabled if the compiler produces broken code or if it does not let us control
base-commit: b13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3
2.36.1
On 6/17/22 11:08, Nathan Chancellor wrote:
When clang is invoked without a '--target' flag, code is generated for the default target, which is usually the host (it is configurable via cmake). As a result, the has-stack-protector scripts will generate code for the default target but check for x86 specific segment registers, which cannot succeed if the default target is not x86.
I guess the real root cause here is the direct use of '$(CC)' without any other flags. Adding '$(CLANG_FLAGS)' seems like a pretty normal fix, like in scripts/Kconfig.include.
I suspect there's another one of these here:
arch/x86/um/vdso/Makefile: cmd_vdso = $(CC) -nostdlib -o $@
but I wouldn't be surprised if UML doesn't work with clang in the first place.
On Wed, Jul 06, 2022 at 03:25:51PM -0700, Dave Hansen wrote:
On 6/17/22 11:08, Nathan Chancellor wrote:
When clang is invoked without a '--target' flag, code is generated for the default target, which is usually the host (it is configurable via cmake). As a result, the has-stack-protector scripts will generate code for the default target but check for x86 specific segment registers, which cannot succeed if the default target is not x86.
I guess the real root cause here is the direct use of '$(CC)' without any other flags. Adding '$(CLANG_FLAGS)' seems like a pretty normal fix, like in scripts/Kconfig.include.
Right, also see the following commits for other areas where this was addressed.
58d746c119df ("efi/libstub: Add $(CLANG_FLAGS) to x86 flags") d5cbd80e302d ("x86/boot: Add $(CLANG_FLAGS) to compressed KBUILD_CFLAGS") 8abe7fc26ad8 ("x86/build: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS)")
I suspect there's another one of these here:
arch/x86/um/vdso/Makefile: cmd_vdso = $(CC) -nostdlib -o $@
but I wouldn't be surprised if UML doesn't work with clang in the first place.
We have started testing UML with clang and it does work but I suspect there is little value to cross compiling a UML kernel, as it has to run in an x86 userland anyways, rather than through QEMU or other virtualization solutions. That is not something I plan to do anyways. If someone does and a fix similar to this one is needed, it can be done at that time.
Thank you for picking up this change!
Cheers, Nathan
linux-stable-mirror@lists.linaro.org
-
Dave Hansen -
Nathan Chancellor