[PATCH] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_rw_attr()

[PATCH] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_rw_attr()

[Jiakai Xu]

Add a null pointer check for imsic_state before dereferencing it in
kvm_riscv_aia_imsic_rw_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.

The crash manifests as:
  Unable to handle kernel paging request at virtual address
  dfffffff00000006
  ...
  kvm_riscv_aia_imsic_rw_attr+0x2d8/0x854 arch/riscv/kvm/aia_imsic.c:958
  aia_set_attr+0x2ee/0x1726 arch/riscv/kvm/aia_device.c:354
  kvm_device_ioctl_attr virt/kvm/kvm_main.c:4744 [inline]
  kvm_device_ioctl+0x296/0x374 virt/kvm/kvm_main.c:4761
  vfs_ioctl fs/ioctl.c:51 [inline]
  ...

The fix adds a check to return -ENODEV if imsic_state is NULL and moves 
isel assignment after imsic_state NULL check.

Fixes: 5463091a51cfaa ("RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
---
 arch/riscv/kvm/aia_imsic.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
index e597e86491c3b..bd7081e70036d 100644
--- a/arch/riscv/kvm/aia_imsic.c
+++ b/arch/riscv/kvm/aia_imsic.c
@@ -952,8 +952,10 @@ int kvm_riscv_aia_imsic_rw_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);
 
 	read_lock_irqsave(&imsic->vsfile_lock, flags);
 
-- 
2.34.1

Re: [PATCH] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_rw_attr()

[Anup Patel]

On Tue, Jan 27, 2026 at 12:52 PM Jiakai Xu <jiakaipeanut@gmail.com> wrote:
>
> Add a null pointer check for imsic_state before dereferencing it in
> kvm_riscv_aia_imsic_rw_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.
>
> The crash manifests as:
>   Unable to handle kernel paging request at virtual address
>   dfffffff00000006
>   ...
>   kvm_riscv_aia_imsic_rw_attr+0x2d8/0x854 arch/riscv/kvm/aia_imsic.c:958
>   aia_set_attr+0x2ee/0x1726 arch/riscv/kvm/aia_device.c:354
>   kvm_device_ioctl_attr virt/kvm/kvm_main.c:4744 [inline]
>   kvm_device_ioctl+0x296/0x374 virt/kvm/kvm_main.c:4761
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   ...
>
> The fix adds a check to return -ENODEV if imsic_state is NULL and moves
> isel assignment after imsic_state NULL check.
>
> Fixes: 5463091a51cfaa ("RISC-V: KVM: Expose IMSIC registers as attributes of AIA irqchip")
> Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
> Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>

LGTM.

Reviewed-by: Anup Patel <anup@brainfault.org>

Queued this for Linux-6.20

Thanks,
Anup


> ---
>  arch/riscv/kvm/aia_imsic.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
> index e597e86491c3b..bd7081e70036d 100644
> --- a/arch/riscv/kvm/aia_imsic.c
> +++ b/arch/riscv/kvm/aia_imsic.c
> @@ -952,8 +952,10 @@ int kvm_riscv_aia_imsic_rw_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);
>
>         read_lock_irqsave(&imsic->vsfile_lock, flags);
>
> --
> 2.34.1
>

Re: [PATCH] RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_rw_attr()

[patchwork-bot+linux-riscv]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Anup Patel <anup@brainfault.org>:

On Tue, 27 Jan 2026 07:22:19 +0000 you wrote:
> Add a null pointer check for imsic_state before dereferencing it in
> kvm_riscv_aia_imsic_rw_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.
> 
> The crash manifests as:
>   Unable to handle kernel paging request at virtual address
>   dfffffff00000006
>   ...
>   kvm_riscv_aia_imsic_rw_attr+0x2d8/0x854 arch/riscv/kvm/aia_imsic.c:958
>   aia_set_attr+0x2ee/0x1726 arch/riscv/kvm/aia_device.c:354
>   kvm_device_ioctl_attr virt/kvm/kvm_main.c:4744 [inline]
>   kvm_device_ioctl+0x296/0x374 virt/kvm/kvm_main.c:4761
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   ...
> 
> [...]

Here is the summary with links:
  - RISC-V: KVM: Fix null pointer dereference in kvm_riscv_aia_imsic_rw_attr()
    https://git.kernel.org/riscv/c/aeb1d17d1af5

You are awesome, thank you!
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