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KVM: VMX: Handle event vectoring error in check_emulate_instruction()
Move handling of emulation during event vectoring, which KVM doesn't support, into VMX's check_emulate_instruction(), so that KVM detects all unsupported emulation, not just cached emulated MMIO (EPT misconfig). E.g. on emulated MMIO that isn't cached (EPT Violation) or occurs with legacy shadow paging (#PF). Rejecting emulation on other sources of emulation also fixes a largely theoretical flaw (thanks to the "unprotect and retry" logic), where KVM could incorrectly inject a #DF: 1. CPU executes an instruction and hits a #GP 2. While vectoring the #GP, a shadow #PF occurs 3. On the #PF VM-Exit, KVM re-injects #GP 4. KVM emulates because of the write-protected page 5. KVM "successfully" emulates and also detects the #GP 6. KVM synthesizes a #GP, and since #GP has already been injected, incorrectly escalates to a #DF. Fix the comment about EMULTYPE_PF as this flag doesn't necessarily mean MMIO anymore: it can also be set due to the write protection violation. Note, handle_ept_misconfig() checks vmx_check_emulate_instruction() before attempting emulation of any kind. Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Ivan Orlov <iorlov@amazon.com> Link: https://lore.kernel.org/r/20241217181458.68690-5-iorlov@amazon.com [sean: massage changelog] Signed-off-by: Sean Christopherson <seanjc@google.com>
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arch/x86/include/asm/kvm_host.h

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2032,8 +2032,8 @@ u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
20322032
* VMware backdoor emulation handles select instructions
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* and reinjects the #GP for all other cases.
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*
2035-
* EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
2036-
* case the CR2/GPA value pass on the stack is valid.
2035+
* EMULTYPE_PF - Set when an intercepted #PF triggers the emulation, in which case
2036+
* the CR2/GPA value pass on the stack is valid.
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*
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* EMULTYPE_COMPLETE_USER_EXIT - Set when the emulator should update interruptibility
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* state and inject single-step #DBs after skipping
@@ -2068,6 +2068,11 @@ u64 vcpu_tsc_khz(struct kvm_vcpu *vcpu);
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#define EMULTYPE_COMPLETE_USER_EXIT (1 << 7)
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#define EMULTYPE_WRITE_PF_TO_SP (1 << 8)
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2071+
static inline bool kvm_can_emulate_event_vectoring(int emul_type)
2072+
{
2073+
return !(emul_type & EMULTYPE_PF);
2074+
}
2075+
20712076
int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
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int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
20732078
void *insn, int insn_len);

arch/x86/kvm/vmx/vmx.c

Lines changed: 9 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -1705,6 +1705,12 @@ int vmx_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
17051705
kvm_queue_exception(vcpu, UD_VECTOR);
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return X86EMUL_PROPAGATE_FAULT;
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}
1708+
1709+
/* Check that emulation is possible during event vectoring */
1710+
if ((to_vmx(vcpu)->idt_vectoring_info & VECTORING_INFO_VALID_MASK) &&
1711+
!kvm_can_emulate_event_vectoring(emul_type))
1712+
return X86EMUL_UNHANDLEABLE_VECTORING;
1713+
17081714
return X86EMUL_CONTINUE;
17091715
}
17101716

@@ -6540,26 +6546,15 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
65406546
return 0;
65416547
}
65426548

6543-
/*
6544-
* Note:
6545-
* Do not try to fix EXIT_REASON_EPT_MISCONFIG if it caused by
6546-
* delivery event since it indicates guest is accessing MMIO.
6547-
* The vm-exit can be triggered again after return to guest that
6548-
* will cause infinite loop.
6549-
*/
65506549
if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
65516550
(exit_reason.basic != EXIT_REASON_EXCEPTION_NMI &&
65526551
exit_reason.basic != EXIT_REASON_EPT_VIOLATION &&
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exit_reason.basic != EXIT_REASON_PML_FULL &&
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exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
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exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
6556-
exit_reason.basic != EXIT_REASON_NOTIFY)) {
6557-
gpa_t gpa = INVALID_GPA;
6558-
6559-
if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG)
6560-
gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
6561-
6562-
kvm_prepare_event_vectoring_exit(vcpu, gpa);
6555+
exit_reason.basic != EXIT_REASON_NOTIFY &&
6556+
exit_reason.basic != EXIT_REASON_EPT_MISCONFIG)) {
6557+
kvm_prepare_event_vectoring_exit(vcpu, INVALID_GPA);
65636558
return 0;
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}
65656560

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