From 66bb8a065f5aedd4551d8d3fbce582972f65c2e1 Mon Sep 17 00:00:00 2001 From: Eric Hankland Date: Wed, 10 Jul 2019 18:25:15 -0700 Subject: KVM: x86: PMU Event Filter Some events can provide a guest with information about other guests or the host (e.g. L3 cache stats); providing the capability to restrict access to a "safe" set of events would limit the potential for the PMU to be used in any side channel attacks. This change introduces a new VM ioctl that sets an event filter. If the guest attempts to program a counter for any blacklisted or non-whitelisted event, the kernel counter won't be created, so any RDPMC/RDMSR will show 0 instances of that event. Signed-off-by: Eric Hankland [Lots of changes. All remaining bugs are probably mine. - Paolo] Signed-off-by: Paolo Bonzini --- arch/x86/kvm/pmu.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+) (limited to 'arch/x86/kvm/pmu.c') diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index dd745b58ffd8..9d92c4d3cd44 100644 --- a/arch/x86/kvm/pmu.c +++ b/arch/x86/kvm/pmu.c @@ -22,6 +22,9 @@ #include "lapic.h" #include "pmu.h" +/* This keeps the total size of the filter under 4k. */ +#define KVM_PMU_EVENT_FILTER_MAX_EVENTS 63 + /* NOTE: * - Each perf counter is defined as "struct kvm_pmc"; * - There are two types of perf counters: general purpose (gp) and fixed. @@ -144,6 +147,10 @@ void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel) { unsigned config, type = PERF_TYPE_RAW; u8 event_select, unit_mask; + struct kvm *kvm = pmc->vcpu->kvm; + struct kvm_pmu_event_filter *filter; + int i; + bool allow_event = true; if (eventsel & ARCH_PERFMON_EVENTSEL_PIN_CONTROL) printk_once("kvm pmu: pin control bit is ignored\n"); @@ -155,6 +162,22 @@ void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel) if (!(eventsel & ARCH_PERFMON_EVENTSEL_ENABLE) || !pmc_is_enabled(pmc)) return; + filter = srcu_dereference(kvm->arch.pmu_event_filter, &kvm->srcu); + if (filter) { + for (i = 0; i < filter->nevents; i++) + if (filter->events[i] == + (eventsel & AMD64_RAW_EVENT_MASK_NB)) + break; + if (filter->action == KVM_PMU_EVENT_ALLOW && + i == filter->nevents) + allow_event = false; + if (filter->action == KVM_PMU_EVENT_DENY && + i < filter->nevents) + allow_event = false; + } + if (!allow_event) + return; + event_select = eventsel & ARCH_PERFMON_EVENTSEL_EVENT; unit_mask = (eventsel & ARCH_PERFMON_EVENTSEL_UMASK) >> 8; @@ -351,3 +374,43 @@ void kvm_pmu_destroy(struct kvm_vcpu *vcpu) { kvm_pmu_reset(vcpu); } + +int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp) +{ + struct kvm_pmu_event_filter tmp, *filter; + size_t size; + int r; + + if (copy_from_user(&tmp, argp, sizeof(tmp))) + return -EFAULT; + + if (tmp.action != KVM_PMU_EVENT_ALLOW && + tmp.action != KVM_PMU_EVENT_DENY) + return -EINVAL; + + if (tmp.nevents > KVM_PMU_EVENT_FILTER_MAX_EVENTS) + return -E2BIG; + + size = struct_size(filter, events, tmp.nevents); + filter = kmalloc(size, GFP_KERNEL_ACCOUNT); + if (!filter) + return -ENOMEM; + + r = -EFAULT; + if (copy_from_user(filter, argp, size)) + goto cleanup; + + /* Ensure nevents can't be changed between the user copies. */ + *filter = tmp; + + mutex_lock(&kvm->lock); + rcu_swap_protected(kvm->arch.pmu_event_filter, filter, + mutex_is_locked(&kvm->lock)); + mutex_unlock(&kvm->lock); + + synchronize_srcu_expedited(&kvm->srcu); + r = 0; +cleanup: + kfree(filter); + return r; +} -- cgit v1.2.3