[tip: x86/urgent] x86/cpu: Fix up srso_safe_ret() and __x86_return_thunk()

["tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     af023ef335f13c8b579298fc432daeef609a9e60
Gitweb:        https://git.kernel.org/tip/af023ef335f13c8b579298fc432daeef609a9e60
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Mon, 14 Aug 2023 13:44:28 +02:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Wed, 16 Aug 2023 09:39:16 +02:00

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
---
 arch/x86/lib/retpoline.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 9427480..a478eb5 100644
--- 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)