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@xxxxxxxxx/
By the way, do you need a re-based version of the guest PBES feature ?
Thanks,
Like Xu
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
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] =
