[PATCH v2 13/13] KVM: x86: Protect pmu_intel.c from Spectre-v1/L1TF attacks

Marios Pomonis
2019-12-11T20:49:19Z

This fixes Spectre-v1/L1TF vulnerabilities in intel_find_fixed_event()
and intel_rdpmc_ecx_to_pmc().
kvm_rdpmc() (ancestor of intel_find_fixed_event()) and
reprogram_fixed_counter() (ancestor of intel_rdpmc_ecx_to_pmc()) are
exported symbols so KVM should treat them conservatively from a security
perspective.

Fixes: commit 25462f7f5295 ("KVM: x86/vPMU: Define kvm_pmu_ops to support vPMU function dispatch")

Signed-off-by: Nick Finco <nifi@google.com>
Signed-off-by: Marios Pomonis <pomonis@google.com>
Reviewed-by: Andrew Honig <ahonig@google.com>
Cc: stable@vger.kernel.org
---
arch/x86/kvm/vmx/pmu_intel.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 7023138b1cb0..34a3a17bb6d7 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -86,10 +86,14 @@ static unsigned intel_find_arch_event(struct kvm_pmu *pmu,

static unsigned intel_find_fixed_event(int idx)
{
- if (idx >= ARRAY_SIZE(fixed_pmc_events))
+ u32 event;
+ size_t size = ARRAY_SIZE(fixed_pmc_events);
+
+ if (idx >= size)
return PERF_COUNT_HW_MAX;

- return intel_arch_events[fixed_pmc_events[idx]].event_type;
+ event = fixed_pmc_events[array_index_nospec(idx, size)];
+ return intel_arch_events[event].event_type;
}

/* check if a PMC is enabled by comparing it with globl_ctrl bits. */
@@ -130,16 +134,20 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
bool fixed = idx & (1u << 30);
struct kvm_pmc *counters;
+ unsigned int num_counters;

idx &= ~(3u << 30);
- if (!fixed && idx >= pmu->nr_arch_gp_counters)
- return NULL;
- if (fixed && idx >= pmu->nr_arch_fixed_counters)
+ if (fixed) {
+ counters = pmu->fixed_counters;
+ num_counters = pmu->nr_arch_fixed_counters;
+ } else {
+ counters = pmu->gp_counters;
+ num_counters = pmu->nr_arch_gp_counters;
+ }
+ if (idx >= num_counters)
return NULL;
- counters = fixed ? pmu->fixed_counters : pmu->gp_counters;
*mask &= pmu->counter_bitmask[fixed ? KVM_PMC_FIXED : KVM_PMC_GP];
-
- return &counters[idx];
+ return &counters[array_index_nospec(idx, num_counters)];
}

static bool intel_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr)
--
2.24.0.525.g8f36a354ae-goog