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KVM: VMX: Handle event vectoring error in check_emulate_instruction()

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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>
This commit is contained in:
Ivan Orlov 2024-12-17 18:14:55 +00:00 committed by Sean Christopherson
parent 704fc6021b
commit 47ef3ef843
2 changed files with 16 additions and 16 deletions
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9
arch/x86/include/asm/kvm_host.h
View File

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

23
arch/x86/kvm/vmx/vmx.c
View File

@ -1705,6 +1705,12 @@ int vmx_check_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
kvm_queue_exception(vcpu, UD_VECTOR);
return X86EMUL_PROPAGATE_FAULT;
}
/* Check that emulation is possible during event vectoring */
if ((to_vmx(vcpu)->idt_vectoring_info & VECTORING_INFO_VALID_MASK) &&
!kvm_can_emulate_event_vectoring(emul_type))
return X86EMUL_UNHANDLEABLE_VECTORING;
return X86EMUL_CONTINUE;
}
@ -6540,26 +6546,15 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
return 0;
}
/*
* Note:
* Do not try to fix EXIT_REASON_EPT_MISCONFIG if it caused by
* delivery event since it indicates guest is accessing MMIO.
* The vm-exit can be triggered again after return to guest that
* will cause infinite loop.
*/
if ((vectoring_info & VECTORING_INFO_VALID_MASK) &&
(exit_reason.basic != EXIT_REASON_EXCEPTION_NMI &&
exit_reason.basic != EXIT_REASON_EPT_VIOLATION &&
exit_reason.basic != EXIT_REASON_PML_FULL &&
exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
exit_reason.basic != EXIT_REASON_NOTIFY)) {
gpa_t gpa = INVALID_GPA;
if (exit_reason.basic == EXIT_REASON_EPT_MISCONFIG)
gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
kvm_prepare_event_vectoring_exit(vcpu, gpa);
exit_reason.basic != EXIT_REASON_NOTIFY &&
exit_reason.basic != EXIT_REASON_EPT_MISCONFIG)) {
kvm_prepare_event_vectoring_exit(vcpu, INVALID_GPA);
return 0;
}