[PATCH] RISC-V: KVM: Fix potential UAF in kvm_riscv_aia_imsic_has_attr()

[PATCH] RISC-V: KVM: Fix potential UAF in kvm_riscv_aia_imsic_has_attr()

[Jiakai Xu]

The KVM_DEV_RISCV_AIA_GRP_APLIC branch of aia_has_attr() was identified
to have a race condition with concurrent KVM_SET_DEVICE_ATTR ioctls,
leading to a use-after-free bug.

Upon analyzing the code, it was discovered that the
KVM_DEV_RISCV_AIA_GRP_IMSIC branch of aia_has_attr() suffers from the same
lack of synchronization. It invokes kvm_riscv_aia_imsic_has_attr() without
holding dev->kvm->lock.

While aia_has_attr() is running, a concurrent aia_set_attr() could call
aia_init() under the dev->kvm->lock. If aia_init() fails, it may trigger
kvm_riscv_vcpu_aia_imsic_cleanup(), which frees imsic_state. Without proper
locking, kvm_riscv_aia_imsic_has_attr() could attempt to access imsic_state
while it is being deallocated.

Although this specific path has not yet been reported by a fuzzer, it
is logically identical to the APLIC issue. Fix this by acquiring the
dev->kvm->lock before calling kvm_riscv_aia_imsic_has_attr(), ensuring
consistency with the locking pattern used for other AIA attribute groups.

Fixes: 5463091a51cf ("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_device.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
index fb901947aefe..9a45c85239fe 100644
--- a/arch/riscv/kvm/aia_device.c
+++ b/arch/riscv/kvm/aia_device.c
@@ -471,7 +471,10 @@ static int aia_has_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
 		mutex_unlock(&dev->kvm->lock);
 		break;
 	case KVM_DEV_RISCV_AIA_GRP_IMSIC:
-		return kvm_riscv_aia_imsic_has_attr(dev->kvm, attr->attr);
+		mutex_lock(&dev->kvm->lock);
+		r = kvm_riscv_aia_imsic_has_attr(dev->kvm, attr->attr);
+		mutex_unlock(&dev->kvm->lock);
+		break;
 	}
 
 	return r;
-- 
2.34.1

Re: [PATCH] RISC-V: KVM: Fix potential UAF in kvm_riscv_aia_imsic_has_attr()

[Anup Patel]

On Wed, Mar 4, 2026 at 1:38 PM Jiakai Xu <xujiakai2025@iscas.ac.cn> wrote:
>
> The KVM_DEV_RISCV_AIA_GRP_APLIC branch of aia_has_attr() was identified
> to have a race condition with concurrent KVM_SET_DEVICE_ATTR ioctls,
> leading to a use-after-free bug.
>
> Upon analyzing the code, it was discovered that the
> KVM_DEV_RISCV_AIA_GRP_IMSIC branch of aia_has_attr() suffers from the same
> lack of synchronization. It invokes kvm_riscv_aia_imsic_has_attr() without
> holding dev->kvm->lock.
>
> While aia_has_attr() is running, a concurrent aia_set_attr() could call
> aia_init() under the dev->kvm->lock. If aia_init() fails, it may trigger
> kvm_riscv_vcpu_aia_imsic_cleanup(), which frees imsic_state. Without proper
> locking, kvm_riscv_aia_imsic_has_attr() could attempt to access imsic_state
> while it is being deallocated.
>
> Although this specific path has not yet been reported by a fuzzer, it
> is logically identical to the APLIC issue. Fix this by acquiring the
> dev->kvm->lock before calling kvm_riscv_aia_imsic_has_attr(), ensuring
> consistency with the locking pattern used for other AIA attribute groups.
>
> Fixes: 5463091a51cf ("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 patch as fix for Linux-7.0-rcX

Thanks,
Anup


> ---
>  arch/riscv/kvm/aia_device.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
> index fb901947aefe..9a45c85239fe 100644
> --- a/arch/riscv/kvm/aia_device.c
> +++ b/arch/riscv/kvm/aia_device.c
> @@ -471,7 +471,10 @@ static int aia_has_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>                 mutex_unlock(&dev->kvm->lock);
>                 break;
>         case KVM_DEV_RISCV_AIA_GRP_IMSIC:
> -               return kvm_riscv_aia_imsic_has_attr(dev->kvm, attr->attr);
> +               mutex_lock(&dev->kvm->lock);
> +               r = kvm_riscv_aia_imsic_has_attr(dev->kvm, attr->attr);
> +               mutex_unlock(&dev->kvm->lock);
> +               break;
>         }
>
>         return r;
> --
> 2.34.1
>

Re: [PATCH] RISC-V: KVM: Fix potential UAF in kvm_riscv_aia_imsic_has_attr()

[patchwork-bot+linux-riscv]

Hello:

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

On Wed,  4 Mar 2026 08:08:04 +0000 you wrote:
> The KVM_DEV_RISCV_AIA_GRP_APLIC branch of aia_has_attr() was identified
> to have a race condition with concurrent KVM_SET_DEVICE_ATTR ioctls,
> leading to a use-after-free bug.
> 
> Upon analyzing the code, it was discovered that the
> KVM_DEV_RISCV_AIA_GRP_IMSIC branch of aia_has_attr() suffers from the same
> lack of synchronization. It invokes kvm_riscv_aia_imsic_has_attr() without
> holding dev->kvm->lock.
> 
> [...]

Here is the summary with links:
  - RISC-V: KVM: Fix potential UAF in kvm_riscv_aia_imsic_has_attr()
    https://git.kernel.org/riscv/c/7120a9d9e023

You are awesome, thank you!
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