linux-kernel - [PATCH] KVM: nVMX: Store vmcs.EXIT_QUALIFICATION as an unsigned long, not u32

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Message-Id: <20200423001127.13490-1-sean.j.christopherson@intel.com>
Date:   Wed, 22 Apr 2020 17:11:27 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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
Subject: [PATCH] KVM: nVMX: Store vmcs.EXIT_QUALIFICATION as an unsigned long, not u32

Use an unsigned long for 'exit_qual' in nested_vmx_reflect_vmexit(), the
EXIT_QUALIFICATION field is naturally sized, not a 32-bit field.

The bug is most easily observed by doing VMXON (or any VMX instruction)
in L2 with a negative displacement, in which case dropping the upper
bits on nested VM-Exit results in L1 calculating the wrong virtual
address for the memory operand, e.g. "vmxon -0x8(%rbp)" yields:

  Unhandled cpu exception 14 #PF at ip 0000000000400553
  rbp=0000000000537000 cr2=0000000100536ff8

Fixes: fbdd50250396d ("KVM: nVMX: Move VM-Fail check out of nested_vmx_exit_reflected()")
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---

Sadly (for me), I can't blame a mishandled merge on this one.  Even more
embarassing is that this is actually the second instance where I botched
the size for exit_qual, you'd think I'd have double-checked everything
after the first one...

 arch/x86/kvm/vmx/nested.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f228339cd0a0..3f32f81f5c59 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5814,7 +5814,8 @@ bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 exit_reason = vmx->exit_reason;
-	u32 exit_intr_info, exit_qual;
+	unsigned long exit_qual;
+	u32 exit_intr_info;

 	WARN_ON_ONCE(vmx->nested.nested_run_pending);

-- 
2.26.0