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>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cbfd1fdb514ad68c854dbbe683c5e2478c9b2e1a..1a09ac99132c01ea09fc7227c59c3b932925c509 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -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);

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b6ce17bf74d775b989c9cbdca0766f0d16db1140..e93c48ff61c5a2a7f52f932d6acc5291f9cd9d49 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -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;
        }