Messages in this thread Patch in this message | | | Date | Mon, 1 Mar 2021 08:52:13 -0800 | From | Sean Christopherson <> | Subject | Re: [PATCH 19/25] KVM: VMX: Add basic handling of VM-Exit from SGX enclave |
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On Mon, Mar 01, 2021, Kai Huang wrote: > 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). */
> + return false; > + } > return true; > }
...
> @@ -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 >
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