linux-kernel - [PATCH AUTOSEL 5.15 07/42] x86/sev: Avoid using __x86_return

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Date:   Tue, 19 Jul 2022 21:13:15 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Kim Phillips <kim.phillips@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Sasha Levin <sashal@...nel.org>, dave.hansen@...ux.intel.com,
        luto@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, x86@...nel.org
Subject: [PATCH AUTOSEL 5.15 07/42] x86/sev: Avoid using __x86_return_thunk

From: Kim Phillips <kim.phillips@....com>

[ Upstream commit 0ee9073000e8791f8b134a8ded31bcc767f7f232 ]

Specifically, it's because __enc_copy() encrypts the kernel after
being relocated outside the kernel in sme_encrypt_execute(), and the
RET macro's jmp offset isn't amended prior to execution.

Signed-off-by: Kim Phillips <kim.phillips@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-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/mm/mem_encrypt_boot.S | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_boot.S b/arch/x86/mm/mem_encrypt_boot.S
index 3d1dba05fce4..d94dea450fa6 100644
--- a/arch/x86/mm/mem_encrypt_boot.S
+++ b/arch/x86/mm/mem_encrypt_boot.S
@@ -65,7 +65,9 @@ SYM_FUNC_START(sme_encrypt_execute)
 	movq	%rbp, %rsp		/* Restore original stack pointer */
 	pop	%rbp
 
-	RET
+	/* Offset to __x86_return_thunk would be wrong here */
+	ret
+	int3
 SYM_FUNC_END(sme_encrypt_execute)
 
 SYM_FUNC_START(__enc_copy)
@@ -151,6 +153,8 @@ SYM_FUNC_START(__enc_copy)
 	pop	%r12
 	pop	%r15
 
-	RET
+	/* Offset to __x86_return_thunk would be wrong here */
+	ret
+	int3
 .L__enc_copy_end:
 SYM_FUNC_END(__enc_copy)
-- 
2.35.1