The make_xfence_request() function uses a shift operation to check if a vCPU is in the hart mask: if (!(hmask & (1UL << (vcpu->vcpu_id - hbase)))) However, when the difference between vcpu_id and hbase is >= BITS_PER_LONG, the shift operation causes undefined behavior. This was detected by UBSAN: UBSAN: shift-out-of-bounds in arch/riscv/kvm/tlb.c:343:23 shift exponent 256 is too large for 64-bit type 'long unsigned int' Fix this by adding a bounds check before the shift operation. This bug was found by fuzzing the KVM RISC-V interface. Fixes: 13acfec2dbcc ("RISC-V: KVM: Add remote HFENCE functions based on VCPU requests") Signed-off-by: Jiakai Xu Signed-off-by: Jiakai Xu --- V1 -> V2: - Dropped 'idx' variable and compared vcpu_id against hbase directly, as suggested by Andrew Jones. --- arch/riscv/kvm/tlb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/riscv/kvm/tlb.c b/arch/riscv/kvm/tlb.c index ff1aeac4eb8eb..439c20c2775ab 100644 --- a/arch/riscv/kvm/tlb.c +++ b/arch/riscv/kvm/tlb.c @@ -338,7 +338,8 @@ static void make_xfence_request(struct kvm *kvm, bitmap_zero(vcpu_mask, KVM_MAX_VCPUS); kvm_for_each_vcpu(i, vcpu, kvm) { if (hbase != -1UL) { - if (vcpu->vcpu_id < hbase) + if (vcpu->vcpu_id < hbase || + vcpu->vcpu_id >= hbase + BITS_PER_LONG) continue; if (!(hmask & (1UL << (vcpu->vcpu_id - hbase)))) continue; -- 2.34.1