linux-kernel - [PATCH v2 5/9] KVM: nVMX: Truncate bits 63:32 of VMCS field on nested check in !64-bit

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Message-Id: <20210422022128.3464144-6-seanjc@google.com>
Date:   Wed, 21 Apr 2021 19:21:24 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Babu Moger <babu.moger@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH v2 5/9] KVM: nVMX: Truncate bits 63:32 of VMCS field on nested
 check in !64-bit

Drop bits 63:32 of the VMCS field encoding when checking for a nested
VM-Exit on VMREAD/VMWRITE in !64-bit mode.  VMREAD and VMWRITE always
use 32-bit operands outside of 64-bit mode.

The actual emulation of VMREAD/VMWRITE does the right thing, this bug is
purely limited to incorrectly causing a nested VM-Exit if a GPR happens
to have bits 63:32 set outside of 64-bit mode.

Fixes: a7cde481b6e8 ("KVM: nVMX: Do not forward VMREAD/VMWRITE VMExits to L1 if required so by vmcs12 vmread/vmwrite bitmaps")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 8b111682fe5c..0e580305a1ee 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5743,7 +5743,7 @@ static bool nested_vmx_exit_handled_vmcs_access(struct kvm_vcpu *vcpu,
 
 	/* Decode instruction info and find the field to access */
 	vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
-	field = kvm_register_read(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
+	field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
 
 	/* Out-of-range fields always cause a VM exit from L2 to L1 */
 	if (field >> 15)
-- 
2.31.1.498.g6c1eba8ee3d-goog