[PATCH 3/7] Revert "KVM: x86/pmu: Accept 0 for absent PMU MSRs when host-initiated if !enable_pmu"

Sean Christopherson
2022-06-11T00:58:19Z

Eating reads and writes to all "PMU" MSRs when there is no PMU is wildly
broken as it results in allowing accesses to _any_ MSR on Intel CPUs
as intel_is_valid_msr() returns true for all host_initiated accesses.

A revert of commit d1c88a402056 ("KVM: x86: always allow host-initiated
writes to PMU MSRs") will soon follow.

This reverts commit 8e6a58e28b34e8d247e772159b8fa8f6bae39192.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/pmu.c | 8 --------
arch/x86/kvm/svm/pmu.c | 11 +----------
2 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 6a32092460d3..87483e503c46 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -442,19 +442,11 @@ static void kvm_pmu_mark_pmc_in_use(struct kvm_vcpu *vcpu, u32 msr)

int kvm_pmu_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
- if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu) {
- msr_info->data = 0;
- return 0;
- }
-
return static_call(kvm_x86_pmu_get_msr)(vcpu, msr_info);
}

int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
{
- if (msr_info->host_initiated && !vcpu->kvm->arch.enable_pmu)
- return !!msr_info->data;
-
kvm_pmu_mark_pmc_in_use(vcpu, msr_info->index);
return static_call(kvm_x86_pmu_set_msr)(vcpu, msr_info);
}
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index fe520b2649b5..256244b8f89c 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -182,16 +182,7 @@ static struct kvm_pmc *amd_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
static bool amd_is_valid_msr(struct kvm_vcpu *vcpu, u32 msr, bool host_initiated)
{
/* All MSRs refer to exactly one PMC, so msr_idx_to_pmc is enough. */
- if (!host_initiated)
- return false;
-
- switch (msr) {
- case MSR_K7_EVNTSEL0 ... MSR_K7_PERFCTR3:
- case MSR_F15H_PERF_CTL0 ... MSR_F15H_PERF_CTR5:
- return true;
- default:
- return false;
- }
+ return false;
}

static struct kvm_pmc *amd_msr_idx_to_pmc(struct kvm_vcpu *vcpu, u32 msr)
--
2.36.1.476.g0c4daa206d-goog