* [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
@ 2021-09-03 7:55 Jiang Jiasheng
2021-09-03 11:44 ` Vitaly Kuznetsov
0 siblings, 1 reply; 5+ messages in thread
From: Jiang Jiasheng @ 2021-09-03 7:55 UTC (permalink / raw)
To: pbonzini, seanjc, vkuznets, wanpengli, jmattson, joro, tglx,
mingo, bp, x86, hpa, jarkko, dave.hansen
Cc: kvm, linux-kernel, linux-sgx, Jiang Jiasheng
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.
Signed-off-by: Jiang Jiasheng <jiasheng@iscas.ac.cn>
---
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0f4a46..c59013c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2871,7 +2871,7 @@ 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 (atomic_read(&(v->kvm)->online_vcpus) > 0 && v == kvm_get_vcpu(v->kvm, 0))
kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
return 0;
}
--
2.7.4
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
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
0 siblings, 1 reply; 5+ messages in thread
From: Vitaly Kuznetsov @ 2021-09-03 11:44 UTC (permalink / raw)
To: Jiang Jiasheng
Cc: kvm, linux-kernel, linux-sgx, Jiang Jiasheng, pbonzini, seanjc,
wanpengli, jmattson, joro, tglx, mingo, bp, x86, hpa, jarkko,
dave.hansen
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.
> Signed-off-by: Jiang Jiasheng <jiasheng@iscas.ac.cn>
> ---
> arch/x86/kvm/x86.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e0f4a46..c59013c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2871,7 +2871,7 @@ 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 (atomic_read(&(v->kvm)->online_vcpus) > 0 && v == kvm_get_vcpu(v->kvm, 0))
> kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
> return 0;
> }
--
Vitaly
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
2021-09-03 11:44 ` Vitaly Kuznetsov
@ 2021-09-03 15:03 ` Sean Christopherson
2021-09-06 11:07 ` Vitaly Kuznetsov
0 siblings, 1 reply; 5+ messages in thread
From: Sean Christopherson @ 2021-09-03 15:03 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: Jiang Jiasheng, kvm, linux-kernel, linux-sgx, pbonzini,
wanpengli, jmattson, joro, tglx, mingo, bp, x86, hpa, jarkko,
dave.hansen
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))
kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
return 0;
}
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
2021-09-03 15:03 ` Sean Christopherson
@ 2021-09-06 11:07 ` Vitaly Kuznetsov
2021-09-08 18:42 ` Sean Christopherson
0 siblings, 1 reply; 5+ messages in thread
From: Vitaly Kuznetsov @ 2021-09-06 11:07 UTC (permalink / raw)
To: Sean Christopherson
Cc: Jiang Jiasheng, kvm, linux-kernel, linux-sgx, pbonzini,
wanpengli, jmattson, joro, tglx, mingo, bp, x86, hpa, jarkko,
dave.hansen
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'.
> kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
> return 0;
> }
>
--
Vitaly
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 4/4] KVM: X86: Potential 'index out of range' bug
2021-09-06 11:07 ` Vitaly Kuznetsov
@ 2021-09-08 18:42 ` Sean Christopherson
0 siblings, 0 replies; 5+ messages in thread
From: Sean Christopherson @ 2021-09-08 18:42 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: Jiang Jiasheng, kvm, linux-kernel, linux-sgx, pbonzini,
wanpengli, jmattson, joro, tglx, mingo, bp, x86, hpa, jarkko,
dave.hansen
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!
^ permalink raw reply [flat|nested] 5+ messages in thread
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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
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