[PATCH 6.1 129/197] KVM: x86/pmu: Fix type length error when reading pmu->fixed_ctr_ctrl

Greg Kroah-Hartman
2024-02-20T21:04:41Z

From: Mingwei Zhang <mizhang@google.com>

commit 05519c86d6997cfb9bb6c82ce1595d1015b718dc upstream.

Use a u64 instead of a u8 when taking a snapshot of pmu->fixed_ctr_ctrl
when reprogramming fixed counters, as truncating the value results in KVM
thinking fixed counter 2 is already disabled (the bug also affects fixed
counters 3+, but KVM doesn't yet support those). As a result, if the
guest disables fixed counter 2, KVM will get a false negative and fail to
reprogram/disable emulation of the counter, which can leads to incorrect
counts and spurious PMIs in the guest.

Fixes: 76d287b2342e ("KVM: x86/pmu: Drop "u8 ctrl, int idx" for reprogram_fixed_counter()")
Cc: stable@vger.kernel.org
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20240123221220.3911317-1-mizhang@google.com
[sean: rewrite changelog to call out the effects of the bug]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/vmx/pmu_intel.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -38,7 +38,7 @@ static int fixed_pmc_events[] = {1, 0, 7
static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data)
{
struct kvm_pmc *pmc;
- u8 old_fixed_ctr_ctrl = pmu->fixed_ctr_ctrl;
+ u64 old_fixed_ctr_ctrl = pmu->fixed_ctr_ctrl;
int i;

pmu->fixed_ctr_ctrl = data;