Re: [PATCH v8 12/12] efi/libstub: disable SCS
From: Ard Biesheuvel <hidden>
Date: 2020-02-19 07:41:05
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On Wed, 19 Feb 2020 at 01:09, Sami Tolvanen [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Disable SCS for the EFI stub and allow x18 to be used. Suggested-by: James Morse <james.morse@arm.com> Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- drivers/firmware/efi/libstub/Makefile | 3 +++ 1 file changed, 3 insertions(+)diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 98a81576213d..dff9fa5a3f1c 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile@@ -30,6 +30,9 @@ KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \ $(call cc-option,-fno-stack-protector) \ -D__DISABLE_EXPORTS +# remove SCS flags from all objects in this directory +KBUILD_CFLAGS := $(filter-out -ffixed-x18 $(CC_FLAGS_SCS), $(KBUILD_CFLAGS)) +
I don't see why you'd need to remove -ffixed-x18 again here. Not using x18 anywhere in the kernel is a much more maintainable approach. In fact, now that I think of it, the EFI AArch64 platform binding forbids the use of x18, so it would be better to add the -ffixed-x18 unconditionally for arm64 (even though the reason it forbids it is to ensure compatibility with an OS using it as a platform register, and so nothing is actually broken atm).
GCOV_PROFILE := n KASAN_SANITIZE := n UBSAN_SANITIZE := n -- 2.25.0.265.gbab2e86ba0-goog
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