RISC-V: KVM: Fix NULL pointer dereference in AIA IMSIC functions

Fuzzer reported a NULL pointer dereference in
kvm_riscv_vcpu_aia_imsic_put() when a VCPU's imsic_state was NULL while
kvm_riscv_aia_initialized() returned true.

The global initialized flag is set per-VM in aia_init(), but imsic_state
is allocated per-VCPU in kvm_riscv_vcpu_aia_imsic_init(). If a VCPU is
created after aia_init() has already run, its imsic_state remains NULL
while the global flag is true. When this VCPU is preempted, kvm_sched_out()
calls kvm_arch_vcpu_put() -> kvm_riscv_vcpu_aia_put() ->
kvm_riscv_vcpu_aia_imsic_put() which dereferences NULL.

Add NULL pointer guards to kvm_riscv_vcpu_aia_imsic_put(), consistent with
the NULL checks already present in all other functions in the same file.

Also add a NULL guard to kvm_riscv_vcpu_aia_imsic_release() and
kvm_riscv_vcpu_aia_imsic_has_interrupt() for the same reason.

Fixes: 4cec89db80ba ("RISC-V: KVM: Move HGEI[E|P] CSR access to IMSIC virtualization")
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Assisted-by: YuanSheng:DeepSeek-V3.2
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260526031517.1166025-1-xujiakai2025@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index 8786f52cf65a2c6570901afe66c57df8ddaf0b02..d38f5de0834c5bb0f4cfbe92da7d60893d13d500 100644 (file)
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -683,6 +683,9 @@ bool kvm_riscv_vcpu_aia_imsic_has_interrupt(struct kvm_vcpu *vcpu)
        unsigned long flags;
        bool ret = false;
 
+       if (!imsic)
+               return false;
+
        /*
         * The IMSIC SW-file directly injects interrupt via hvip so
         * only check for interrupt when IMSIC VS-file is being used.
@@ -722,6 +725,9 @@ void kvm_riscv_vcpu_aia_imsic_put(struct kvm_vcpu *vcpu)
        struct imsic *imsic = vcpu->arch.aia_context.imsic_state;
        unsigned long flags;
 
+       if (!imsic)
+               return;
+
        if (!kvm_vcpu_is_blocking(vcpu))
                return;
 
@@ -738,6 +744,9 @@ void kvm_riscv_vcpu_aia_imsic_release(struct kvm_vcpu *vcpu)
        int old_vsfile_hgei, old_vsfile_cpu;
        struct imsic *imsic = vcpu->arch.aia_context.imsic_state;
 
+       if (!imsic)
+               return;
+
        /* Read and clear IMSIC VS-file details */
        write_lock_irqsave(&imsic->vsfile_lock, flags);
        old_vsfile_hgei = imsic->vsfile_hgei;