linux-kernel - [PATCH] RISC-V: KVM: Skip IMSIC update if vCPU IMSIC state is not initialized

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Message-Id: <20260127084313.3496485-1-xujiakai2025@iscas.ac.cn>
Date: Tue, 27 Jan 2026 08:43:13 +0000
From: Jiakai Xu <jiakaipeanut@...il.com>
To: linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	kvm-riscv@...ts.infradead.org,
	kvm@...r.kernel.org
Cc: Anup Patel <anup@...infault.org>,
	Atish Patra <atish.patra@...ux.dev>,
	Paul Walmsley <pjw@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alex@...ti.fr>,
	Jiakai Xu <xujiakai2025@...as.ac.cn>,
	Jiakai Xu <jiakaiPeanut@...il.com>
Subject: [PATCH] RISC-V: KVM: Skip IMSIC update if vCPU IMSIC state is not initialized

kvm_riscv_vcpu_aia_imsic_update() assumes that the vCPU IMSIC state has
already been initialized and unconditionally accesses imsic->vsfile_lock.
However, in fuzzed ioctl sequences, the AIA device may be initialized at
the VM level while the per-vCPU IMSIC state is still NULL.

This leads to invalid access when entering the vCPU run loop before
IMSIC initialization has completed.

The crash manifests as:
  Unable to handle kernel paging request at virtual address
  dfffffff00000006
  ...
  kvm_riscv_vcpu_aia_imsic_update arch/riscv/kvm/aia_imsic.c:801
  kvm_riscv_vcpu_aia_update arch/riscv/kvm/aia_device.c:493
  kvm_arch_vcpu_ioctl_run arch/riscv/kvm/vcpu.c:927
  ...

Add a guard to skip the IMSIC update path when imsic_state is NULL. This
allows the vCPU run loop to continue safely.

This issue was discovered during fuzzing of RISC-V KVM code.

Fixes: db8b7e97d6137a ("RISC-V: KVM: Add in-kernel virtualization of AIA IMSIC")
Signed-off-by: Jiakai Xu <xujiakai2025@...as.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@...il.com>
---
 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 e597e86491c3b..a7d387e280d49 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -797,6 +797,10 @@ int kvm_riscv_vcpu_aia_imsic_update(struct kvm_vcpu *vcpu)
 	if (kvm->arch.aia.mode == KVM_DEV_RISCV_AIA_MODE_EMUL)
 		return 1;

+	/* IMSIC vCPU state may not be initialized yet */
+	if (!imsic)
+		return 1;
+
 	/* Read old IMSIC VS-file details */
 	read_lock_irqsave(&imsic->vsfile_lock, flags);
 	old_vsfile_hgei = imsic->vsfile_hgei;
-- 
2.34.1