Re: [PATCH v6 10/10] drm/tyr: add BO-related ioctls

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential
issues to consider:
- [High] drm/tyr: slab-out-of-bounds access in bo_mmap_offset() on
  imported or dumb BOs
- [Medium] drm/tyr: NO_MMAP buffer objects remain mappable via mmap()
  and PRIME
--

commit 31c4893f869db54a6627810d48273b6077efa3af
Author: Alvin Sun <alvin.sun@linux.dev>

drm/tyr: add BO-related ioctls

This commit implements the PANTHOR_BO_CREATE and PANTHOR_BO_MMAP_OFFSET
ioctls for allocating GEM buffer objects and retrieving their mmap offsets.

> diff --git a/drivers/gpu/drm/tyr/file.rs b/drivers/gpu/drm/tyr/file.rs
> index b982e8db2c4c1..f99bb2992d87a 100644
> --- a/drivers/gpu/drm/tyr/file.rs
> +++ b/drivers/gpu/drm/tyr/file.rs

[ ... ]

> +    pub(crate) fn bo_mmap_offset(
> +        ddev: &TyrDrmDevice<Registered>,
> +        _reg_data: &TyrDrmRegistrationData<'_>,
> +        bommap: &mut uapi::drm_panthor_bo_mmap_offset,
> +        file: &TyrDrmFile,
> +    ) -> Result<u32> {
> +        if bommap.pad != 0 {
> +            dev_dbg!(
> +                ddev.as_ref(),
> +                "BO mmap offset pad not zero: {}\n",
> +                bommap.pad
> +            );
> +            return Err(EINVAL);
> +        }
> +
> +        let bo = crate::gem::lookup_handle(file, bommap.handle).inspect_err(|_| {
> +            dev_dbg!(ddev.as_ref(), "Invalid BO mmap handle: {}\n", bommap.handle);
> +        })?;

[Severity: High]
Can passing a PRIME-imported or dumb-buffer handle to bo_mmap_offset() read
past the end of the GEM object allocation when bo.flags() is called below?

rust/kernel/drm/gem/shmem.rs:Object::ALLOC_OPS {
    ...
        gem_create_object: None,
    ...
        gem_prime_import_sg_table: Some(bindings::drm_gem_shmem_prime_import_sg_table),
        dumb_create: Some(bindings::drm_gem_shmem_dumb_create),
    ...
}

Because gem_create_object is None while gem_prime_import_sg_table and
dumb_create are wired up, DRM_IOCTL_PRIME_FD_TO_HANDLE (or
DRM_IOCTL_MODE_CREATE_DUMB) calls __drm_gem_shmem_create() and allocates a
bare struct drm_gem_shmem_object rather than a gem::shmem::Object<BoData>.
lookup_handle() casts that pointer to gem::shmem::Object<BoData>, so calling
bo.flags() reads self.inner.flags out of bounds in the slab allocation.

> +        if bo.flags() & uapi::drm_panthor_bo_flags_DRM_PANTHOR_BO_NO_MMAP != 0 {
> +            dev_dbg!(ddev.as_ref(), "BO mmap offset on NO_MMAP object\n");
> +            return Err(EPERM);
> +        }

[Severity: Medium]
Can userspace still CPU-map a DRM_PANTHOR_BO_NO_MMAP buffer object despite
this check?

In bo_create(), new_object() calls __drm_gem_shmem_init(), which allocates
the object's VMA offset via drm_gem_create_mmap_offset(), and
bo.create_handle() authorizes that offset for the file via
drm_vma_node_allow().  Because gem::shmem::Object<BoData>::VTABLE sets mmap
directly to drm_gem_shmem_object_mmap() without inspecting BoData::flags,
userspace can export a DRM_PANTHOR_BO_NO_MMAP handle with
DRM_IOCTL_PRIME_HANDLE_TO_FD and mmap() the returned dma-buf fd (or mmap()
the DRM fd directly using the pre-allocated VMA offset).

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261109-tyr-ioctls-v6-0-b2896bf2b3c9@kylinos.cn?part=10