CVE-2024-58091: drm/fbdev-dma: Add shadow buffering for deferred I/O

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

Description
===========

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.

The Linux kernel CVE team has assigned CVE-2024-58091 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.11 with commit 5ab91447aa13b8b98bc11f5326f33500b0ee2c48 and fixed in 6.13.6 with commit cdc581169942de3b9e2648cfbd98c5ff9111c2c8
	Issue introduced in 6.11 with commit 5ab91447aa13b8b98bc11f5326f33500b0ee2c48 and fixed in 6.14 with commit 3603996432997f7c88da37a97062a46cda01ac9d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-58091
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/drm_fbdev_dma.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/cdc581169942de3b9e2648cfbd98c5ff9111c2c8
	https://git.kernel.org/stable/c/3603996432997f7c88da37a97062a46cda01ac9d