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KVM: x86: PMU Event Filter

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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 <ehankland@google.com>
[Lots of changes. All remaining bugs are probably mine. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eric Hankland
2019-07-10 18:25:15 -07:00
committed by Paolo Bonzini
parent cdc238eb72
commit 66bb8a065f
7 changed files with 110 additions and 0 deletions
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63
arch/x86/kvm/pmu.c
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@@ -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;
}