linux-kernel - [PATCH v4] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_has

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Message-Id: <20260125143344.2515451-1-xujiakai2025@iscas.ac.cn>
Date: Sun, 25 Jan 2026 14:33:44 +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: Alexandre Ghiti <alex@...ti.fr>,
	Albert Ou <aou@...s.berkeley.edu>,
	Palmer Dabbelt <palmer@...belt.com>,
	Paul Walmsley <pjw@...nel.org>,
	Atish Patra <atish.patra@...ux.dev>,
	Anup Patel <anup@...infault.org>,
	Jiakai Xu <xujiakai2025@...as.ac.cn>,
	Jiakai Xu <jiakaiPeanut@...il.com>
Subject: [PATCH v4] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_has_attr()

Add a null pointer check for imsic_state before dereferencing it in
kvm_riscv_aia_imsic_has_attr(). While the function checks that the
vcpu exists, it doesn't verify that the vcpu's imsic_state has been
initialized, leading to a null pointer dereference when accessed.

This issue was discovered during fuzzing of RISC-V KVM code. The
crash occurs when userspace calls KVM_HAS_DEVICE_ATTR ioctl on an
AIA IMSIC device before the IMSIC state has been fully initialized
for a vcpu.

The crash manifests as:
  Unable to handle kernel paging request at virtual address
  dfffffff00000001
  ...
  epc : kvm_riscv_aia_imsic_has_attr+0x464/0x50e
  arch/riscv/kvm/aia_imsic.c:998
  ...
  kvm_riscv_aia_imsic_has_attr+0x464/0x50e arch/riscv/kvm/aia_imsic.c:998
  aia_has_attr+0x128/0x2bc arch/riscv/kvm/aia_device.c:471
  kvm_device_ioctl_attr virt/kvm/kvm_main.c:4722 [inline]
  kvm_device_ioctl+0x296/0x374 virt/kvm/kvm_main.c:4739
  ...

The fix adds a check to return -ENODEV if imsic_state is NULL, which
is consistent with other error handling in the function and prevents
the null pointer dereference.

Fixes: 5463091a51cf ("RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <xujiakai2025@...as.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@...il.com>
---
V3 -> V4: Fix typo in Signed-off-by email address.
V2 -> V3: Moved isel assignment after imsic_state NULL check.
          Placed patch version history after '---' separator.
          Added parentheses to function name in subject.
V1 -> V2: Added Fixes tag and drop external link as suggested.

 arch/riscv/kvm/aia_imsic.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index e597e86491c3b..cd070d83663a9 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -993,8 +993,11 @@ int kvm_riscv_aia_imsic_has_attr(struct kvm *kvm, unsigned long type)
 	if (!vcpu)
 		return -ENODEV;

-	isel = KVM_DEV_RISCV_AIA_IMSIC_GET_ISEL(type);
 	imsic = vcpu->arch.aia_context.imsic_state;
+	if (!imsic)
+		return -ENODEV;
+
+	isel = KVM_DEV_RISCV_AIA_IMSIC_GET_ISEL(type);
 	return imsic_mrif_isel_check(imsic->nr_eix, isel);
 }

-- 
2.34.1