On Mon, 1 Mar 2021 08:52:13 -0800 Sean Christopherson wrote:

On Mon, Mar 01, 2021, Kai Huang wrote:

quoted

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 50810d471462..df8e338267aa 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c

@@ -1570,12 +1570,18 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
 
 static bool vmx_can_emulate_instruction(struct kvm_vcpu *vcpu, void *insn, int insn_len)
 {
+	if (to_vmx(vcpu)->exit_reason.enclave_mode) {
+		kvm_queue_exception(vcpu, UD_VECTOR);

Rereading my own code, I think it would be a good idea to add a comment here
explaining that injecting #UD is technically wrong, but avoids giving guest
userspace an easy way to DoS the guest.  The EPT misconfig is a good example;
guest userspace could have executed a simple MOV <reg>, <mem> instruction, in
which case injecting a #UD is bizarre behavior.  But, the alternative is exiting
to userspace with KVM_INTERNAL_ERROR_EMULATION, which is all but guaranteed to
kill the guest.

If KVM, specifically handle_emulation_failure(), ever gains a more sophisticated
mechanism for handling userspace emulation errors, this should be updated too.

	/*
	 * Emulation of instructions in SGX enclaves is impossible as RIP does
	 * not point  tthe failing instruction, and even if it did, the code
	 * stream is inaccessible.  Inject #UD instead of exiting to userspace
	 * so that guest userspace can't DoS the guest simply by triggering
	 * emulation (enclaves are CPL3 only).
	 */

Agreed. Will add above comment.

quoted

+		return false;
+	}
 	return true;
 }

...

quoted

@@ -5384,6 +5415,9 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
 {
 	gpa_t gpa;
 
+	if (!vmx_can_emulate_instruction(vcpu, NULL, 0))
+		return 1;
+
 	/*
 	 * A nested guest cannot optimize MMIO vmexits, because we have an
 	 * nGPA here instead of the required GPA.

-- 
2.29.2