[PATCH v3 1/2] RISC-V: KVM: Fix array out-of-bounds in pmu_ctr_read() and pmu_fw_ctr_read_hi()

[Jiakai Xu]

When a guest invokes SBI_EXT_PMU_COUNTER_FW_READ or
SBI_EXT_PMU_COUNTER_FW_READ_HI on a firmware counter that has not been
configured via SBI_EXT_PMU_COUNTER_CFG_MATCH, the pmc->event_idx remains
SBI_PMU_EVENT_IDX_INVALID (0xFFFFFFFF). get_event_code() extracts the
lower 16 bits, yielding 0xFFFF (65535), which is then used to index into
kvpmu->fw_event[]. Since fw_event is only RISCV_KVM_MAX_FW_CTRS (32)
entries, this triggers an array-index-out-of-bounds:

  UBSAN: array-index-out-of-bounds in arch/riscv/kvm/vcpu_pmu.c:255:37
  index 65535 is out of range for type 'kvm_fw_event [32]'

Add a check for the known unconfigured case (SBI_PMU_EVENT_IDX_INVALID)
and a WARN_ONCE guard for any unexpected out-of-bounds event codes,
returning -EINVAL in both cases.

Fixes: badc386869e2c ("RISC-V: KVM: Support firmware events")
Fixes: 08fb07d6dcf71 ("RISC-V: KVM: Support 64 bit firmware counters on RV32")
Signed-off-by: Jiakai Xu <xujiakai2025 at iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut at gmail.com>
---
V2 -> V3:
- Added check for SBI_PMU_EVENT_IDX_INVALID.
- Added WARN_ONCE for unexpected out-of-bounds event codes.
V1 -> V2:
- Merged the fixes for pmu_ctr_read() and pmu_fw_ctr_read_hi() into a single
commit.
- Removed the pr_warn, simply returning -EINVAL instead.
---
 arch/riscv/kvm/vcpu_pmu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index e873430e596b..c87a7b0037cf 100644
--- a/arch/riscv/kvm/vcpu_pmu.c
+++ b/arch/riscv/kvm/vcpu_pmu.c
@@ -226,7 +226,14 @@ static int pmu_fw_ctr_read_hi(struct kvm_vcpu *vcpu, unsigned long cidx,
 	if (pmc->cinfo.type != SBI_PMU_CTR_TYPE_FW)
 		return -EINVAL;
 
+	if (pmc->event_idx == SBI_PMU_EVENT_IDX_INVALID)
+		return -EINVAL;
+
 	fevent_code = get_event_code(pmc->event_idx);
+	if (WARN_ONCE(fevent_code >= SBI_PMU_FW_MAX,
+				  "Invalid firmware event code: %d\n", fevent_code))
+		return -EINVAL;
+
 	pmc->counter_val = kvpmu->fw_event[fevent_code].value;
 
 	*out_val = pmc->counter_val >> 32;
@@ -251,7 +258,14 @@ static int pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
 	pmc = &kvpmu->pmc[cidx];
 
 	if (pmc->cinfo.type == SBI_PMU_CTR_TYPE_FW) {
+		if (pmc->event_idx == SBI_PMU_EVENT_IDX_INVALID)
+			return -EINVAL;
+
 		fevent_code = get_event_code(pmc->event_idx);
+		if (WARN_ONCE(fevent_code >= SBI_PMU_FW_MAX,
+					  "Invalid firmware event code: %d\n", fevent_code))
+			return -EINVAL;
+
 		pmc->counter_val = kvpmu->fw_event[fevent_code].value;
 	} else if (pmc->perf_event) {
 		pmc->counter_val += perf_event_read_value(pmc->perf_event, &enabled, &running);
-- 
2.34.1