From 47c28d436f409f5b009dc82bd82d4971088aa391 Mon Sep 17 00:00:00 2001
From: Denis Valeev <lemniscattaden@gmail.com>
Date: Sat, 22 Jan 2022 23:13:57 +0300
Subject: [PATCH] KVM: x86: nSVM: skip eax alignment check for non-SVM instructions
Git-commit: 47c28d436f409f5b009dc82bd82d4971088aa391
Patch-mainline: v5.17-rc2
References: git-fixes

The bug occurs on #GP triggered by VMware backdoor when eax value is
unaligned. eax alignment check should not be applied to non-SVM
instructions because it leads to incorrect omission of the instructions
emulation.
Apply the alignment check only to SVM instructions to fix.

Fixes: d1cba6c92237 ("KVM: x86: nSVM: test eax for 4K alignment for GP errata workaround")
Signed-off-by: Denis Valeev <lemniscattaden@gmail.com>
Message-id: <Yexlhaoe1Fscm59u@q>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 arch/x86/kvm/svm/svm.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 6d31d357a83b..ec05f8bfc21b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2091,10 +2091,6 @@ static int gp_interception(struct kvm_vcpu *vcpu)
 	if (error_code)
 		goto reinject;
 
-	/* All SVM instructions expect page aligned RAX */
-	if (svm->vmcb->save.rax & ~PAGE_MASK)
-		goto reinject;
-
 	/* Decode the instruction for usage later */
 	if (x86_decode_emulated_instruction(vcpu, 0, NULL, 0) != EMULATION_OK)
 		goto reinject;
@@ -2112,8 +2108,13 @@ static int gp_interception(struct kvm_vcpu *vcpu)
 		if (!is_guest_mode(vcpu))
 			return kvm_emulate_instruction(vcpu,
 				EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
-	} else
+	} else {
+		/* All SVM instructions expect page aligned RAX */
+		if (svm->vmcb->save.rax & ~PAGE_MASK)
+			goto reinject;
+
 		return emulate_svm_instr(vcpu, opcode);
+	}
 
 reinject:
 	kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
-- 
2.35.3