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[v4,0/2] RISC-V: KVM: Fix array out-of-bounds in firmware counter reads

Message ID 20260312011931.1352239-1-xujiakai2025@iscas.ac.cn
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Series RISC-V: KVM: Fix array out-of-bounds in firmware counter reads | expand

Message

Jiakai Xu March 12, 2026, 1:19 a.m. UTC 
When a guest reads a firmware PMU counter via
SBI_EXT_PMU_COUNTER_FW_READ or SBI_EXT_PMU_COUNTER_FW_READ_HI without
first configuring it with SBI_EXT_PMU_COUNTER_CFG_MATCH, the counter's
event_idx remains SBI_PMU_EVENT_IDX_INVALID (0xFFFFFFFF).

get_event_code() extracts the lower 16 bits from event_idx, yielding
0xFFFF, which is then used to index into kvpmu->fw_event[]. Since the
fw_event array only contains RISCV_KVM_MAX_FW_CTRS entries, this results
in an out-of-bounds access that can be detected by UBSAN.

Patch 1 fixes the issue by validating the firmware event code before
accessing the fw_event array and returning -EINVAL for invalid values.

After fixing the kernel behavior, the existing KVM selftest
(sbi_pmu_test) fails because it attempts to read firmware counters
without configuring them first. Patch 2 updates the selftest to
configure a firmware event before reading the counter and adds a
negative test to ensure that reading an unconfigured firmware counter
fails gracefully.

Jiakai Xu (2):
  RISC-V: KVM: Fix array out-of-bounds in pmu_ctr_read() and
    pmu_fw_ctr_read_hi()
  RISC-V: KVM: selftests: Fix firmware counter read in sbi_pmu_test

 arch/riscv/kvm/vcpu_pmu.c                     | 14 +++++++
 .../testing/selftests/kvm/include/riscv/sbi.h | 37 +++++++++++++++++++
 .../selftests/kvm/riscv/sbi_pmu_test.c        | 20 +++++++++-
 3 files changed, 70 insertions(+), 1 deletion(-)