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 <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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@ -4065,6 +4065,32 @@ KVM_ARM_VCPU_FINALIZE call.
See KVM_ARM_VCPU_INIT for details of vcpu features that require finalization
using this ioctl.
4.120 KVM_SET_PMU_EVENT_FILTER
Capability: KVM_CAP_PMU_EVENT_FILTER
Architectures: x86
Type: vm ioctl
Parameters: struct kvm_pmu_event_filter (in)
Returns: 0 on success, -1 on error
struct kvm_pmu_event_filter {
__u32 action;
__u32 nevents;
__u64 events[0];
};
This ioctl restricts the set of PMU events that the guest can program.
The argument holds a list of events which will be allowed or denied.
The eventsel+umask of each event the guest attempts to program is compared
against the events field to determine whether the guest should have access.
This only affects general purpose counters; fixed purpose counters can
be disabled by changing the perfmon CPUID leaf.
Valid values for 'action':
#define KVM_PMU_EVENT_ALLOW 0
#define KVM_PMU_EVENT_DENY 1
5. The kvm_run structure
------------------------

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@ -933,6 +933,8 @@ struct kvm_arch {
bool guest_can_read_msr_platform_info;
bool exception_payload_enabled;
struct kvm_pmu_event_filter *pmu_event_filter;
};
struct kvm_vm_stat {

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@ -422,4 +422,14 @@ struct kvm_nested_state {
__u8 data[0];
};
/* for KVM_CAP_PMU_EVENT_FILTER */
struct kvm_pmu_event_filter {
__u32 action;
__u32 nevents;
__u64 events[0];
};
#define KVM_PMU_EVENT_ALLOW 0
#define KVM_PMU_EVENT_DENY 1
#endif /* _ASM_X86_KVM_H */

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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;
}

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@ -118,6 +118,7 @@ void kvm_pmu_refresh(struct kvm_vcpu *vcpu);
void kvm_pmu_reset(struct kvm_vcpu *vcpu);
void kvm_pmu_init(struct kvm_vcpu *vcpu);
void kvm_pmu_destroy(struct kvm_vcpu *vcpu);
int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp);
bool is_vmware_backdoor_pmc(u32 pmc_idx);

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@ -3132,6 +3132,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_SET_BOOT_CPU_ID:
case KVM_CAP_SPLIT_IRQCHIP:
case KVM_CAP_IMMEDIATE_EXIT:
case KVM_CAP_PMU_EVENT_FILTER:
case KVM_CAP_GET_MSR_FEATURES:
case KVM_CAP_MSR_PLATFORM_INFO:
case KVM_CAP_EXCEPTION_PAYLOAD:
@ -4978,6 +4979,9 @@ set_identity_unlock:
r = kvm_vm_ioctl_hv_eventfd(kvm, &hvevfd);
break;
}
case KVM_SET_PMU_EVENT_FILTER:
r = kvm_vm_ioctl_set_pmu_event_filter(kvm, argp);
break;
default:
r = -ENOTTY;
}
@ -9428,6 +9432,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
kvm_ioapic_destroy(kvm);
kvm_free_vcpus(kvm);
kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
kvm_mmu_uninit_vm(kvm);
kvm_page_track_cleanup(kvm);
kvm_hv_destroy_vm(kvm);

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@ -995,6 +995,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_ARM_SVE 170
#define KVM_CAP_ARM_PTRAUTH_ADDRESS 171
#define KVM_CAP_ARM_PTRAUTH_GENERIC 172
#define KVM_CAP_PMU_EVENT_FILTER 173
#ifdef KVM_CAP_IRQ_ROUTING
@ -1329,6 +1330,8 @@ struct kvm_s390_ucas_mapping {
#define KVM_PPC_GET_RMMU_INFO _IOW(KVMIO, 0xb0, struct kvm_ppc_rmmu_info)
/* Available with KVM_CAP_PPC_GET_CPU_CHAR */
#define KVM_PPC_GET_CPU_CHAR _IOR(KVMIO, 0xb1, struct kvm_ppc_cpu_char)
/* Available with KVM_CAP_PMU_EVENT_FILTER */
#define KVM_SET_PMU_EVENT_FILTER _IOW(KVMIO, 0xb2, struct kvm_pmu_event_filter)
/* ioctl for vm fd */
#define KVM_CREATE_DEVICE _IOWR(KVMIO, 0xe0, struct kvm_create_device)