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.

v2: add Fixes tag and drop external link as suggested.

Fixes: 5463091a51cf ("RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
---
 arch/riscv/kvm/aia_imsic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index e597e86491c3b..9c58a66068447 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -995,6 +995,9 @@ int kvm_riscv_aia_imsic_has_attr(struct kvm *kvm, unsigned long type)
 
 	isel = KVM_DEV_RISCV_AIA_IMSIC_GET_ISEL(type);
 	imsic = vcpu->arch.aia_context.imsic_state;
+	if (!imsic)
+		return -ENODEV;
+
 	return imsic_mrif_isel_check(imsic->nr_eix, isel);
 }
 
-- 
2.34.1

…
> 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.

How do you think about to move the assignment for the local variable “isel”
behind this check by another update step?
https://elixir.bootlin.com/linux/v6.19-rc5/source/arch/riscv/kvm/aia_imsic.c#L982-L999


> v2: add Fixes tag and drop external link as suggested.

Please move a patch version description behind the marker line.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.19-rc6#n785


Would it be helpful to append parentheses to a function name also in the summary phrase?

Regards,
Markus

Thanks, will address in v3.

Best regards,
Jiakai

Markus Elfring <Markus.Elfring@web.de> 于2026年1月25日周日 19:30写道：
>
> …
> > 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.
>
> How do you think about to move the assignment for the local variable “isel”
> behind this check by another update step?
> https://elixir.bootlin.com/linux/v6.19-rc5/source/arch/riscv/kvm/aia_imsic.c#L982-L999
>
>
> > v2: add Fixes tag and drop external link as suggested.
>
> Please move a patch version description behind the marker line.
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.19-rc6#n785
>
>
> Would it be helpful to append parentheses to a function name also in the summary phrase?
>
> Regards,
> Markus