Re: [PATCH v1 1/4] iommufd: Set upper bounds on cache invalidation entry_num and entry_len

[Baolu Lu]

On 6/4/26 05:26, Nicolin Chen wrote:
> iommufd_hwpt_invalidate() takes a user-controlled entry_num and entry_len,
> each bounded only by U32_MAX. An entry_len beyond the kernel's struct size
> makes the copy helper verify the extra bytes are zero, scanning that excess
> in one uninterruptible pass; a multi-gigabyte value over zeroed user memory
> trips the soft-lockup watchdog.
>
> A large entry_num is the other half, driving the backend invalidation loop
> with no reschedule. The VT-d nested handler, for one, copies each entry and
> flushes caches per iteration, pinning the CPU on a non-preemptible kernel.
>
> Cap both in the ioctl. entry_len is held under PAGE_SIZE, above any request
> struct, and entry_num under 1 << 19, the order of a hardware invalidation
> queue and well beyond any real batch, bounding the per-call loop length.
>
> Fixes: 8c6eabae3807 ("iommufd: Add IOMMU_HWPT_INVALIDATE")
> Cc:stable@xxxxxxxxxxxxxxx
> Assisted-by:Claude:claude-opus-4-8
> Signed-off-by: Nicolin Chen<nicolinc@xxxxxxxxxx>
> ---
>   drivers/iommu/iommufd/hw_pagetable.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>