linux-kernel - [PATCH 0/2] KVM: x86: Fix RM exception injection bugs

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Message-ID: <20230322143300.2209476-1-seanjc@google.com>
Date:   Wed, 22 Mar 2023 07:32:58 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 0/2] KVM: x86: Fix RM exception injection bugs

Fix two bugs introduced by a semi-recent fix for AMD's Page Real Mode.

Patch 1 was tested against the syzkaller testcase that exposed the bug[*].

Patch 2 was testing by enabling the VMware backdoor in L1 to turn on #GP
interception, hacking L0 KVM to passthrough MSR_IA32_VMX_BASIC to L1
and then writing the MSR from L2 while in Real Mode, thus forcing L0 KVM
to emulate the WRMSR from L2 and synthesiz a #GP VM-Exit into L1.
Confirmed that bad behavior in L1 with an assertion:

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index bcac3efcde41..ef3bb5ab9654 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5178,6 +5178,9 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
        vect_info = vmx->idt_vectoring_info;
        intr_info = vmx_get_intr_info(vcpu);
 
+       WARN_ONCE((intr_info & INTR_INFO_DELIVER_CODE_MASK) && !is_protmode(vcpu),
+                 "Exception VM-Exit shouldn't report error code when CPU is in Real Mode");
+
        /*
         * Machine checks are handled by handle_exception_irqoff(), or by
         * vmx_vcpu_run() if a #MC occurs on VM-Entry.  NMIs are handled by

[*] https://lkml.kernel.org/r/ZBNrWZQhMX8AHzWM%40google.com

Sean Christopherson (2):
  KVM: x86: Clear "has_error_code", not "error_code", for RM exception
    injection
  KVM: nVMX: Do not report error code when synthesizing VM-Exit from
    Real Mode

 arch/x86/kvm/vmx/nested.c |  7 ++++++-
 arch/x86/kvm/x86.c        | 11 +++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)


base-commit: 45dd9bc75d9adc9483f0c7d662ba6e73ed698a0b
-- 
2.40.0.rc2.332.ga46443480c-goog