linux-kernel - [PATCH 03/14] KVM: x86: nSVM: test eax for 4K alignment for GP errata workaround

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Date:   Tue, 14 Sep 2021 18:48:14 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>, Bandan Das <bsd@...hat.com>,
        linux-kernel@...r.kernel.org (open list),
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Wei Huang <wei.huang2@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kselftest@...r.kernel.org (open list:KERNEL SELFTEST FRAMEWORK),
        Maxim Levitsky <mlevitsk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Shuah Khan <shuah@...nel.org>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: [PATCH 03/14] KVM: x86: nSVM: test eax for 4K alignment for GP errata workaround

GP SVM errata workaround made the #GP handler always emulate
the SVM instructions.

However these instructions #GP in case the operand is not 4K aligned,
but the workaround code didn't check this and we ended up
emulating these instructions anyway.

This is only an emulation accuracy check bug as there is no harm for
KVM to read/write unaligned vmcb images.

Fixes: 82a11e9c6fa2 ("KVM: SVM: Add emulation support for #GP triggered by SVM instructions")

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b2e710a3fff6..6645542df9bd 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2224,6 +2224,10 @@ 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;
-- 
2.26.3