x86/cpu: Fix up srso_safe_ret() and __x86_return_thunk()

  vmlinux.o: warning: objtool: srso_untrain_ret() falls through to next function __x86_return_skl()
  vmlinux.o: warning: objtool: __x86_return_thunk() falls through to next function __x86_return_skl()

This is because these functions (can) end with CALL, which objtool
does not consider a terminating instruction. Therefore, replace the
INT3 instruction (which is a non-fatal trap) with UD2 (which is a
fatal-trap).

This indicates execution will not continue past this point.

Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.637802730@infradead.org

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 9427480cfae98f0dd75f313784886594367e05d1..a478eb5bbf62a8d9df9e4c012657ce1310733d0f 100644 (file)
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -258,7 +258,7 @@ SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL)
        int3
        lfence
        call srso_safe_ret
-       int3
+       ud2
 SYM_CODE_END(srso_safe_ret)
 SYM_FUNC_END(srso_untrain_ret)
 __EXPORT_THUNK(srso_untrain_ret)
@@ -268,7 +268,7 @@ SYM_CODE_START(__x86_return_thunk)
        ANNOTATE_NOENDBR
        ALTERNATIVE_2 "jmp __ret", "call srso_safe_ret", X86_FEATURE_SRSO, \
                        "call srso_safe_ret_alias", X86_FEATURE_SRSO_ALIAS
-       int3
+       ud2
 SYM_CODE_END(__x86_return_thunk)
 EXPORT_SYMBOL(__x86_return_thunk)