Re: [PATCH v2 7/7] KVM: selftests: Test pmu event filter with incompatible kvm_pmu_event_filter

Jinrong Liang
2023-05-25T02:20:03Z

Sean Christopherson <seanjc@google.com> 于2023年5月25日周四 07:50写道：
>
> On Thu, Apr 20, 2023, Jinrong Liang wrote:
> > From: Jinrong Liang <cloudliang@tencent.com>
> >
> > From: Jinrong Liang <cloudliang@tencent.com>
> >
> > Add test to verify the behavior of the pmu event filter when an
> > incomplete kvm_pmu_event_filter structure is used. By running the
> > test, we can ensure that the pmu event filter correctly handles
> > incomplete structures and does not allow events to be counted when
> > they should not be.
> >
> > Signed-off-by: Jinrong Liang <cloudliang@tencent.com>
> > ---
> > .../kvm/x86_64/pmu_event_filter_test.c | 23 +++++++++++++++++++
> > 1 file changed, 23 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/x86_64/pmu_event_filter_test.c b/tools/testing/selftests/kvm/x86_64/pmu_event_filter_test.c
> > index 9be4c6f8fb7e..a6b6e0d086ae 100644
> > --- a/tools/testing/selftests/kvm/x86_64/pmu_event_filter_test.c
> > +++ b/tools/testing/selftests/kvm/x86_64/pmu_event_filter_test.c
> > @@ -881,6 +881,24 @@ static bool fixed_ctr_is_allowed(uint8_t idx, uint32_t action, uint32_t bitmap)
> > (action == KVM_PMU_EVENT_DENY && !(bitmap & BIT_ULL(idx)));
> > }
> >
> > +struct incompatible_pmu_event_filter {
> > + __u32 action;
> > + __u32 nevents;
> > + __u32 fixed_counter_bitmap;
> > +};
> > +
> > +static uint64_t test_incompatible_filter(struct kvm_vcpu *vcpu, uint32_t action,
> > + uint32_t bitmap)
> > +{
> > + struct incompatible_pmu_event_filter err_f;
> > +
> > + err_f.action = action;
> > + err_f.fixed_counter_bitmap = bitmap;
> > + ioctl((vcpu->vm)->fd, KVM_SET_PMU_EVENT_FILTER, &err_f.action);
>
> This is completely busted. It "passes" by luck, not because it's a valid test.
> The size of the argument is embedded in the IOCTL number itself, which means that
> unless glibc is being very nice and using a macro + typeof + sizeof to sanity check
> things, which I highly doubt is the case, this ioctl() is passing random stack data,
> a.k.a. garbage, to KVM.
>
> In short, drop this patch.

Thank you for letting us know about the issues with the patch. I will
drop the patch as suggested. Would you advise me to prepare version 3
to remove this patch?