RISC-V: KVM: Fix array out-of-bounds in pmu_ctr_read() and pmu_fw_ctr_read_hi()

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@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Reviewed-by: Andrew Jones <andrew.jones@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260316014533.2312254-2-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>

diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
index f3bf985dcf432056555cbab230239962a4b77d92..9e9f3302cef85b3fba7f4e92a08c6a8d8bb1de74 100644 (file)
--- 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);