[PATCH v3] RISC-V: KVM: Fix use-after-free in kvm_riscv_aia_aplic_has_attr()

[Anup Patel]

On Mon, Mar 2, 2026 at 6:57 PM Jiakai Xu <xujiakai2025 at iscas.ac.cn> wrote:
>
> Fuzzer reports a KASAN use-after-free bug triggered by a race
> between KVM_HAS_DEVICE_ATTR and KVM_SET_DEVICE_ATTR ioctls on the AIA
> device. The root cause is that aia_has_attr() invokes
> kvm_riscv_aia_aplic_has_attr() without holding dev->kvm->lock, while
> a concurrent aia_set_attr() may call aia_init() under that lock. When
> aia_init() fails after kvm_riscv_aia_aplic_init() has succeeded, it
> calls kvm_riscv_aia_aplic_cleanup() in its fail_cleanup_imsics path,
> which frees both aplic_state and aplic_state->irqs. The concurrent
> has_attr path can then dereference the freed aplic->irqs in
> aplic_read_pending():
>         irqd = &aplic->irqs[irq];   /* UAF here */
>
> KASAN report:
>  BUG: KASAN: slab-use-after-free in aplic_read_pending
>              arch/riscv/kvm/aia_aplic.c:119 [inline]
>  BUG: KASAN: slab-use-after-free in aplic_read_pending_word
>              arch/riscv/kvm/aia_aplic.c:351 [inline]
>  BUG: KASAN: slab-use-after-free in aplic_mmio_read_offset
>              arch/riscv/kvm/aia_aplic.c:406
>  Read of size 8 at addr ff600000ba965d58 by task 9498
>  Call Trace:
>   aplic_read_pending arch/riscv/kvm/aia_aplic.c:119 [inline]
>   aplic_read_pending_word arch/riscv/kvm/aia_aplic.c:351 [inline]
>   aplic_mmio_read_offset arch/riscv/kvm/aia_aplic.c:406
>   kvm_riscv_aia_aplic_has_attr arch/riscv/kvm/aia_aplic.c:566
>   aia_has_attr arch/riscv/kvm/aia_device.c:469
>  allocated by task 9473:
>   kvm_riscv_aia_aplic_init arch/riscv/kvm/aia_aplic.c:583
>   aia_init arch/riscv/kvm/aia_device.c:248 [inline]
>   aia_set_attr arch/riscv/kvm/aia_device.c:334
>  freed by task 9473:
>   kvm_riscv_aia_aplic_cleanup arch/riscv/kvm/aia_aplic.c:644
>   aia_init arch/riscv/kvm/aia_device.c:292 [inline]
>   aia_set_attr arch/riscv/kvm/aia_device.c:334
>
> Fix this race by acquiring dev->kvm->lock in aia_has_attr() before
> calling kvm_riscv_aia_aplic_has_attr(), consistent with the locking
> pattern used in aia_get_attr() and aia_set_attr().
>
> Fixes: 289a007b98b06d ("RISC-V: KVM: Expose APLIC registers as attributes of AIA irqchip")
> Signed-off-by: Jiakai Xu <jiakaiPeanut at gmail.com>
> Signed-off-by: Jiakai Xu <xujiakai2025 at iscas.ac.cn>
> ---
> V2 -> V3:
> - Fixed incorrect locking pattern in aia_has_attr(): avoid returning
>   while holding dev->kvm->lock by storing the return value in a local
>   variable, unlocking, and then returning.
> V1 -> V2:
> - Fixed the race by adding locking in aia_has_attr() instead of
>   introducing a new validation function, as suggested by Anup Patel.
> ---
>  arch/riscv/kvm/aia_device.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
> index b195a93add1ce..0722cbaed5ec9 100644
> --- a/arch/riscv/kvm/aia_device.c
> +++ b/arch/riscv/kvm/aia_device.c
> @@ -437,7 +437,7 @@ static int aia_get_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>
>  static int aia_has_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>  {
> -       int nr_vcpus;
> +       int nr_vcpus, r = -ENXIO;
>
>         switch (attr->group) {
>         case KVM_DEV_RISCV_AIA_GRP_CONFIG:
> @@ -466,12 +466,15 @@ static int aia_has_attr(struct kvm_device *dev, struct kvm_device_attr *attr)
>                 }
>                 break;
>         case KVM_DEV_RISCV_AIA_GRP_APLIC:
> -               return kvm_riscv_aia_aplic_has_attr(dev->kvm, attr->attr);
> +               mutex_lock(&dev->kvm->lock);
> +               r = kvm_riscv_aia_aplic_has_attr(dev->kvm, attr->attr);
> +               mutex_unlock(&dev->kvm->lock);
> +               return r;

This needs to be a "break;" instead of "return r;".
I have taken care at the time of merging.

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

Queued this patch as fix for Linux-7.0-rcX

Regards,
Anup

>         case KVM_DEV_RISCV_AIA_GRP_IMSIC:
>                 return kvm_riscv_aia_imsic_has_attr(dev->kvm, attr->attr);
>         }
>
> -       return -ENXIO;
> +       return r;
>  }
>
>  struct kvm_device_ops kvm_riscv_aia_device_ops = {
> --
> 2.34.1
>