linux-kernel - [PATCH 5.16 051/200] KVM: x86: nSVM: skip eax alignment check for non-SVM instructions

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Message-Id: <20220131105235.285631010@linuxfoundation.org>
Date:   Mon, 31 Jan 2022 11:55:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Denis Valeev <lemniscattaden@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.16 051/200] KVM: x86: nSVM: skip eax alignment check for non-SVM instructions

From: Denis Valeev <lemniscattaden@...il.com>

commit 47c28d436f409f5b009dc82bd82d4971088aa391 upstream.

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@...il.com>
Message-Id: <Yexlhaoe1Fscm59u@q>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/svm/svm.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2306,10 +2306,6 @@ static int gp_interception(struct kvm_vc
 	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;
@@ -2327,8 +2323,13 @@ static int gp_interception(struct kvm_vc
 		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);