linux-kernel - [PATCH v2 02/11] x86/cpu: Fix up srso_safe_ret() and __x86_return

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Message-ID: <20230814121148.637802730@infradead.org>
Date:   Mon, 14 Aug 2023 13:44:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        David.Kaplan@....com, Andrew.Cooper3@...rix.com,
        jpoimboe@...nel.org, gregkh@...uxfoundation.org,
        nik.borisov@...e.com
Subject: [PATCH v2 02/11] 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@...radead.org>
---
 arch/x86/lib/retpoline.S |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -259,7 +259,7 @@ SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLO
 	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)
@@ -269,7 +269,7 @@ SYM_CORE_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)