kvm: vmx: Nested VM-entry prereqs for event inj.

This patch extends the checks done prior to a nested VM entry.
Specifically, it extends the check_vmentry_prereqs function with checks
for fields relevant to the VM-entry event injection information, as
described in the Intel SDM, volume 3.

This patch is motivated by a syzkaller bug, where a bad VM-entry
interruption information field is generated in the VMCS02, which causes
the nested VM launch to fail. Then, KVM fails to resume L1.

While KVM should be improved to correctly resume L1 execution after a
failed nested launch, this change is justified because the existing code
to resume L1 is flaky/ad-hoc and the test coverage for resuming L1 is
sparse.

Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Marc Orr <marcorr@google.com>
[Removed comment whose parts were describing previous revisions and the
 rest was obvious from function/variable naming. - Radim]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 331993c49dae..257f27620bc2 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -110,6 +110,15 @@ static inline bool is_la57_mode(struct kvm_vcpu *vcpu)
 #endif
 }
 
+static inline bool x86_exception_has_error_code(unsigned int vector)
+{
+	static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |
+			BIT(NP_VECTOR) | BIT(SS_VECTOR) | BIT(GP_VECTOR) |
+			BIT(PF_VECTOR) | BIT(AC_VECTOR);
+
+	return (1U << vector) & exception_has_error_code;
+}
+
 static inline bool mmu_is_nested(struct kvm_vcpu *vcpu)
 {
 	return vcpu->arch.walk_mmu == &vcpu->arch.nested_mmu;