CVE-2024-58091

In the Linux kernel, the following vulnerability has been resolved:

drm/fbdev-dma: Add shadow buffering for deferred I/O

DMA areas are not necessarily backed by struct page, so we cannot

rely on it for deferred I/O. Allocate a shadow buffer for drivers

that require deferred I/O and use it as framebuffer memory.

Fixes driver errors about being "Unable to handle kernel NULL pointer

dereference at virtual address" or "Unable to handle kernel paging

request at virtual address".

The patch splits drm_fbdev_dma_driver_fbdev_probe() in an initial

allocation, which creates the DMA-backed buffer object, and a tail

that sets up the fbdev data structures. There is a tail function for

direct memory mappings and a tail function for deferred I/O with

the shadow buffer.

It is no longer possible to use deferred I/O without shadow buffer.

It can be re-added if there exists a reliably test for usable struct

page in the allocated DMA-backed buffer object.