x86: Use -mindirect-branch-cs-prefix for RETPOLINE builds

stable inclusion
from stable-v5.10.133
commit 6849ed81a33ae616bfadf40e5c68af265d106dff
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5YVKO

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6849ed81a33ae616bfadf40e5c68af265d106dff

--------------------------------

commit 68cf4f2a upstream.

In order to further enable commit:

  bbe2df3f ("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: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Reviewed-by: NKees Cook <keescook@chromium.org>
Acked-by: NNick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/20211119165630.276205624@infradead.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

Makefile

@@ -672,6 +672,7 @@ 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