kvm_riscv_vcpu_aia_rmw_topei() assumes that the per-vCPU IMSIC state has been initialized once AIA is reported as available and initialized at the VM level. This assumption does not always hold. Under fuzzed ioctl sequences, a guest may access the IMSIC TOPEI CSR before the vCPU IMSIC state is set up. In this case, vcpu->arch.aia_context.imsic_state is still NULL, and the TOPEI RMW path dereferences it unconditionally, leading to a host kernel crash. The crash manifests as: Unable to handle kernel paging request at virtual address dfffffff0000000e ... kvm_riscv_vcpu_aia_imsic_rmw arch/riscv/kvm/aia_imsic.c:909 kvm_riscv_vcpu_aia_rmw_topei arch/riscv/kvm/aia.c:231 csr_insn arch/riscv/kvm/vcpu_insn.c:208 system_opcode_insn arch/riscv/kvm/vcpu_insn.c:281 kvm_riscv_vcpu_virtual_insn arch/riscv/kvm/vcpu_insn.c:355 kvm_riscv_vcpu_exit arch/riscv/kvm/vcpu_exit.c:230 kvm_arch_vcpu_ioctl_run arch/riscv/kvm/vcpu.c:1008 ... Fix this by explicitly checking whether the vCPU IMSIC state has been initialized before handling TOPEI CSR accesses. If not, forward the CSR emulation to user space. Fixes: db8b7e97d6137 ("RISC-V: KVM: Add in-kernel virtualization of AIA IMSIC") Signed-off-by: Jiakai Xu Signed-off-by: Jiakai Xu --- V1 -> V2: Moved imsic_state NULL check into kvm_riscv_vcpu_aia_imsic_rmw(). Updated Fixes tag to db8b7e97d6137. --- arch/riscv/kvm/aia_imsic.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c index fda0346f0ea1f..60917f4789d84 100644 --- a/arch/riscv/kvm/aia_imsic.c +++ b/arch/riscv/kvm/aia_imsic.c @@ -892,6 +892,10 @@ int kvm_riscv_vcpu_aia_imsic_rmw(struct kvm_vcpu *vcpu, unsigned long isel, int r, rc = KVM_INSN_CONTINUE_NEXT_SEPC; struct imsic *imsic = vcpu->arch.aia_context.imsic_state; + /* If IMSIC vCPU state not initialized then forward to user space */ + if (!imsic) + return KVM_INSN_EXIT_TO_USER_SPACE; + if (isel == KVM_RISCV_AIA_IMSIC_TOPEI) { /* Read pending and enabled interrupt with highest priority */ topei = imsic_mrif_topei(imsic->swfile, imsic->nr_eix, -- 2.34.1