linux-kernel - [PATCH AUTOSEL 5.18 06/54] x86/retpoline: Swizzle retpoline thunk

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Date:   Tue, 19 Jul 2022 21:09:43 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Sasha Levin <sashal@...nel.org>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, ndesaulniers@...gle.com
Subject: [PATCH AUTOSEL 5.18 06/54] x86/retpoline: Swizzle retpoline thunk

From: Peter Zijlstra <peterz@...radead.org>

[ Upstream commit 00e1533325fd1fb5459229fe37f235462649f668 ]

Put the actual retpoline thunk as the original code so that it can
become more complicated. Specifically, it allows RET to be a JMP,
which can't be .altinstr_replacement since that doesn't do relocations
(except for the very first instruction).

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/lib/retpoline.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index b2b2366885a2..2cdd62499d54 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -33,9 +33,9 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\reg, SYM_L_GLOBAL)
 	UNWIND_HINT_EMPTY
 	ANNOTATE_NOENDBR
 
-	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
-		      __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
-		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE
+	ALTERNATIVE_2 __stringify(RETPOLINE \reg), \
+		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_LFENCE, \
+		      __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), ALT_NOT(X86_FEATURE_RETPOLINE)
 
 .endm
 
-- 
2.35.1