linux-kernel - [PATCH 1/3] KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig

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Message-ID: <20240209221700.393189-2-seanjc@google.com>
Date: Fri,  9 Feb 2024 14:16:58 -0800
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
Subject: [PATCH 1/3] KVM: nVMX: Clear EXIT_QUALIFICATION when injecting an EPT Misconfig

Explicitly clear the EXIT_QUALIFCATION field when injecting an EPT
misconfig into L1, as required by the VMX architecture.  Per the SDM:

  This field is saved for VM exits due to the following causes:
  debug exceptions; page-fault exceptions; start-up IPIs (SIPIs);
  system-management interrupts (SMIs) that arrive immediately after the
  execution of I/O instructions; task switches; INVEPT; INVLPG; INVPCID;
  INVVPID; LGDT; LIDT; LLDT; LTR; SGDT; SIDT; SLDT; STR; VMCLEAR; VMPTRLD;
  VMPTRST; VMREAD; VMWRITE; VMXON; WBINVD; WBNOINVD; XRSTORS; XSAVES;
  control-register accesses; MOV DR; I/O instructions; MWAIT; accesses to
  the APIC-access page; EPT violations; EOI virtualization; APIC-write
  emulation; page-modification log full; SPP-related events; and
  instruction timeout. For all other VM exits, this field is cleared.

Generating EXIT_QUALIFICATION from vcpu->arch.exit_qualification is wrong
for all (two) paths that lead to nested_ept_inject_page_fault().  For EPT
violations (the common case), vcpu->arch.exit_qualification will have been
set by handle_ept_violation() to vmcs02.EXIT_QUALIFICATION, i.e. contains
the information of a EPT violation and thus is likely non-zero.

For an EPT misconfig, which can reach FNAME(walk_addr_generic) and thus
inject a nEPT misconfig if KVM created an MMIO SPTE that became stale,
vcpu->arch.exit_qualification will hold the information from the last EPT
violation VM-Exit, as vcpu->arch.exit_qualification is _only_ written by
handle_ept_violation().

Fixes: 4704d0befb07 ("KVM: nVMX: Exiting from L2 to L1")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 994e014f8a50..1eebed84bb65 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -417,10 +417,12 @@ static void nested_ept_inject_page_fault(struct kvm_vcpu *vcpu,
 		vmx->nested.pml_full = false;
 		exit_qualification &= INTR_INFO_UNBLOCK_NMI;
 	} else {
-		if (fault->error_code & PFERR_RSVD_MASK)
+		if (fault->error_code & PFERR_RSVD_MASK) {
 			vm_exit_reason = EXIT_REASON_EPT_MISCONFIG;
-		else
+			exit_qualification = 0;
+		} else {
 			vm_exit_reason = EXIT_REASON_EPT_VIOLATION;
+		}

 		/*
 		 * Although the caller (kvm_inject_emulated_page_fault) would
-- 
2.43.0.687.g38aa6559b0-goog