| Message ID | 1630655700-798374-1-git-send-email-jiasheng@iscas.ac.cn (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | None | expand |
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; > }
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; }
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; > } >
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!
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; }
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(-)