Commit 8589827f authored by Aaron Lewis's avatar Aaron Lewis Committed by Sean Christopherson
Browse files

KVM: x86/pmu: Remove impossible events from the pmu event filter 



If it's not possible for an event in the pmu event filter to match a
pmu event being programmed by the guest, it's pointless to have it in
the list.  Opt for a shorter list by removing those events.

Because this is established uAPI the pmu event filter can't outright
rejected these events as garbage and return an error.  Instead, play
nice and remove them from the list.

Also, opportunistically rewrite the comment when the filter is set to
clarify that it guards against *all* TOCTOU attacks on the verified
data.

Signed-off-by: default avatarAaron Lewis <aaronlewis@google.com>
Link: https://lore.kernel.org/r/20221220161236.555143-3-aaronlewis@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 6a5cba7b

arch/x86/kvm/pmu.c

+18 −1
Original line number Diff line number Diff line
@@ -594,6 +594,21 @@ void kvm_pmu_trigger_event(struct kvm_vcpu *vcpu, u64 perf_hw_id) 
}

EXPORT_SYMBOL_GPL(kvm_pmu_trigger_event);



static void remove_impossible_events(struct kvm_pmu_event_filter *filter)

{

	int i, j;



	for (i = 0, j = 0; i < filter->nevents; i++) {

		if (filter->events[i] & ~(kvm_pmu_ops.EVENTSEL_EVENT |

					  ARCH_PERFMON_EVENTSEL_UMASK))

			continue;



		filter->events[j++] = filter->events[i];

	}



	filter->nevents = j;

}



int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp)

{

	struct kvm_pmu_event_filter tmp, *filter;
@@ -624,9 +639,11 @@ int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp) 
	if (copy_from_user(filter, argp, size))

		goto cleanup;



	/* Ensure nevents can't be changed between the user copies. */

	/* Restore the verified state to guard against TOCTOU attacks. */

	*filter = tmp;



	remove_impossible_events(filter);



	/*

	 * Sort the in-kernel list so that we can search it with bsearch.

	 */