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From:   Jinrong Liang <ljr.kernel@gmail.com>
Date:   Thu, 25 May 2023 10:19:44 +0800
Message-ID: <CAFg_LQWdSnNOd+VwTu8pQezL7qaN=4L_YffHVQUQWJiV5U76wQ@mail.gmail.com>
Subject: Re: [PATCH v2 7/7] KVM: selftests: Test pmu event filter with
 incompatible kvm_pmu_event_filter
To:     Sean Christopherson <seanjc@google.com>
Cc:     Like Xu <like.xu.linux@gmail.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <shuah@kernel.org>,
        Aaron Lewis <aaronlewis@google.com>,
        David Matlack <dmatlack@google.com>,
        Vishal Annapurve <vannapurve@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Jinrong Liang <cloudliang@tencent.com>,
        linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
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Sean Christopherson <seanjc@google.com> =E4=BA=8E2023=E5=B9=B45=E6=9C=8825=
=E6=97=A5=E5=91=A8=E5=9B=9B 07:50=E5=86=99=E9=81=93=EF=BC=9A
>
> 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, uint=
32_t action, uint32_t bitmap)
> >               (action =3D=3D KVM_PMU_EVENT_DENY && !(bitmap & BIT_ULL(i=
dx)));
> >  }
> >
> > +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 =3D action;
> > +     err_f.fixed_counter_bitmap =3D 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 me=
ans that
> unless glibc is being very nice and using a macro + typeof + sizeof to sa=
nity 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?