Messages in this thread | | | Date | Fri, 10 Dec 2021 16:59:29 +0800 | From | Like Xu <> | Subject | Re: [PATCH] KVM: x86: avoid out of bounds indices for fixed performance counters |
| |
On 10/12/2021 3:11 am, Paolo Bonzini wrote: > Because IceLake has 4 fixed performance counters but KVM only supports 3, > it is possible for reprogram_fixed_counters to pass to
Emm, it's possible for a unwise user space or smart syzkaller.
> reprogram_fixed_counter an index that is out of bounds for > the fixed_pmc_events array. > > Ultimately intel_find_fixed_event, which is the only place that uses > fixed_pmc_events, handles this correctly because it checks against the > size of fixed_pmc_events anyway. Every other place > operates on the fixed_counters[] array which is sized > according to INTEL_PMC_MAX_FIXED. However, it is cleaner if > the unsupported performance counters are culled early on > in reprogram_fixed_counters.
How about introducing a static "struct x86_pmu_capability" variable [1] so that we can
(1) setup num_counters_fixed just once in the kvm_init_pmu_capability(), and (2) avoid repeated calls to perf_get_x86_pmu_capability() ;
?
[1] https://lore.kernel.org/kvm/20210806133802.3528-17-lingshan.zhu@intel.com/ By the way, do you need a re-based version of the guest PBES feature ?
Thanks, Like Xu
> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > arch/x86/kvm/vmx/pmu_intel.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > index 1b7456b2177b..d33e9799276e 100644 > --- a/arch/x86/kvm/vmx/pmu_intel.c > +++ b/arch/x86/kvm/vmx/pmu_intel.c > @@ -91,7 +91,7 @@ static unsigned intel_find_fixed_event(int idx) > u32 event; > size_t size = ARRAY_SIZE(fixed_pmc_events); > > - if (idx >= size) > + if (WARN_ON_ONCE(idx >= size)) > return PERF_COUNT_HW_MAX; > > event = fixed_pmc_events[array_index_nospec(idx, size)]; > @@ -500,8 +500,9 @@ static void intel_pmu_refresh(struct kvm_vcpu *vcpu) > pmu->nr_arch_fixed_counters = 0; > } else { > pmu->nr_arch_fixed_counters = > - min_t(int, edx.split.num_counters_fixed, > - x86_pmu.num_counters_fixed); > + min3(ARRAY_SIZE(fixed_pmc_events), > + (size_t) edx.split.num_counters_fixed, > + (size_t) x86_pmu.num_counters_fixed); > edx.split.bit_width_fixed = min_t(int, > edx.split.bit_width_fixed, x86_pmu.bit_width_fixed); > pmu->counter_bitmask[KVM_PMC_FIXED] =
| |