From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jiang Jiasheng <jiasheng@iscas.ac.cn>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-sgx@vger.kernel.org, pbonzini@redhat.com,
wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
x86@kernel.org, hpa@zytor.com, jarkko@kernel.org,
dave.hansen@linux.intel.com
Subject: Re: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
Date: Wed, 8 Sep 2021 18:42:22 +0000 [thread overview]
Message-ID: <YTkEDoe8R5JJ77+B@google.com> (raw)
In-Reply-To: <87tuiy3qtc.fsf@vitty.brq.redhat.com>
On Mon, Sep 06, 2021, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
>
> > On Fri, Sep 03, 2021, Vitaly Kuznetsov wrote:
> >> Jiang Jiasheng <jiasheng@iscas.ac.cn> writes:
> >>
> >> > The kvm_get_vcpu() will call for the array_index_nospec()
> >> > with the value of atomic_read(&(v->kvm)->online_vcpus) as size,
> >> > and the value of constant '0' as index.
> >> > If the size is also '0', it will be unreasonabe
> >> > that the index is no less than the size.
> >> >
> >>
> >> Can this really happen?
> >>
> >> 'online_vcpus' is never decreased, it is increased with every
> >> kvm_vm_ioctl_create_vcpu() call when a new vCPU is created and is set to
> >> 0 when all vCPUs are destroyed (kvm_free_vcpus()).
> >>
> >> kvm_guest_time_update() takes a vcpu as a parameter, this means that at
> >> least 1 vCPU is currently present so 'online_vcpus' just can't be zero.
> >
> > Agreed, but doing kvm_get_vcpu() is ugly and overkill.
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 86539c1686fa..cc1cb9a401cd 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2969,7 +2969,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> > offsetof(struct compat_vcpu_info, time));
> > if (vcpu->xen.vcpu_time_info_set)
> > kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0);
> > - if (v == kvm_get_vcpu(v->kvm, 0))
> > + if (!kvm_vcpu_get_idx(v))
>
> Do we really need to keep kvm_vcpu_get_idx() around though? It has only
> 3 users, all in arch/x86/kvm/hyperv.[ch], and the inline simpy returns
> 'vcpu->vcpu_idx'.
Nope, looks like it's a holdover from before the introduction of vcpu_idx. I'll
send a small series to jettison the wrapper and make the above change.
Thanks!
prev parent reply other threads:[~2021-09-08 18:42 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 7:55 [PATCH 4/4] KVM: X86: Potential 'index out of range' bug Jiang Jiasheng
2021-09-03 11:44 ` Vitaly Kuznetsov
2021-09-03 15:03 ` Sean Christopherson
2021-09-06 11:07 ` Vitaly Kuznetsov
2021-09-08 18:42 ` Sean Christopherson [this message]
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