Commit 22ab0641 authored by Danilo Krummrich's avatar Danilo Krummrich
Browse files

rust: drm: ensure kmalloc() compatible Layout 



drm::Device is allocated through __drm_dev_alloc() (which uses
kmalloc()) and the driver private data, <T as drm::Driver>::Data, is
initialized in-place.

Due to the order of fields in drm::Device

  pub struct Device<T: drm::Driver> {
     dev: Opaque<bindings::drm_device>,
     data: T::Data,
  }

even with an arbitrary large alignment requirement of T::Data it can't
happen that the size of Device is smaller than its alignment requirement.

However, let's not rely on this subtle circumstance and create a proper
kmalloc() compatible Layout.

Fixes: 1e4b8896 ("rust: drm: add device abstraction")
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250731154919.4132-3-dakr@kernel.org


Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent fde578c8

rust/kernel/drm/device.rs

+7 −2
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ 
//! C header: [`include/linux/drm/drm_device.h`](srctree/include/linux/drm/drm_device.h)



use crate::{

    alloc::allocator::Kmalloc,

    bindings, device, drm,

    drm::driver::AllocImpl,

    error::from_err_ptr,
@@ -12,7 +13,7 @@ 
    prelude::*,

    types::{ARef, AlwaysRefCounted, Opaque},

};

use core::{mem, ops::Deref, ptr, ptr::NonNull};

use core::{alloc::Layout, mem, ops::Deref, ptr, ptr::NonNull};



#[cfg(CONFIG_DRM_LEGACY)]

macro_rules! drm_legacy_fields {
@@ -96,6 +97,10 @@ impl<T: drm::Driver> Device<T> { 


    /// Create a new `drm::Device` for a `drm::Driver`.

    pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<ARef<Self>> {

        // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()`

        // compatible `Layout`.

        let layout = Kmalloc::aligned_layout(Layout::new::<Self>());



        // SAFETY:

        // - `VTABLE`, as a `const` is pinned to the read-only section of the compilation,

        // - `dev` is valid by its type invarants,
@@ -103,7 +108,7 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<A 
            bindings::__drm_dev_alloc(

                dev.as_raw(),

                &Self::VTABLE,

                mem::size_of::<Self>(),

                layout.size(),

                mem::offset_of!(Self, dev),

            )

        }