[PATCH 5.15 89/89] x86: Use -mindirect-branch-cs-prefix for RETPOLINE builds

Greg Kroah-Hartman
2022-07-22T09:28:48Z

commit 68cf4f2a72ef8786e6b7af6fd9a89f27ac0f520d upstream.

In order to further enable commit:

bbe2df3f6b6d ("x86/alternative: Try inline spectre_v2=retpoline,amd")

add the new GCC flag -mindirect-branch-cs-prefix:

https://gcc.gnu.org/g:2196a681d7810ad8b227bf983f38ba716620545e
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102952
https://bugs.llvm.org/show_bug.cgi?id=52323

to RETPOLINE=y builds. This should allow fully inlining retpoline,amd
for GCC builds.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20211119165630.276205624@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Makefile | 1 +
1 file changed, 1 insertion(+)

--- a/Makefile
+++ b/Makefile
@@ -687,6 +687,7 @@ endif

ifdef CONFIG_CC_IS_GCC
RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
+RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch-cs-prefix)
RETPOLINE_VDSO_CFLAGS := $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register)
endif
ifdef CONFIG_CC_IS_CLANG