Subject: CVE-2024-41094: drm/fbdev-dma: Only set smem_start is enable per module option

From: Greg Kroah-Hartman <[email-masked]>

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

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

drm/fbdev-dma: Only set smem_start is enable per module option

Only export struct fb_info.fix.smem_start if that is required by the
user and the memory does not come from vmalloc().

Setting struct fb_info.fix.smem_start breaks systems where DMA
memory is backed by vmalloc address space. An example error is
shown below.

[    3.536043] ------------[ cut here ]------------
[    3.540716] virt_to_phys used for non-linear address: 000000007fc4f540 (0xffff800086001000)
[    3.552628] WARNING: CPU: 4 PID: 61 at arch/arm64/mm/physaddr.c:12 __virt_to_phys+0x68/0x98
[    3.565455] Modules linked in:
[    3.568525] CPU: 4 PID: 61 Comm: kworker/u12:5 Not tainted 6.6.23-06226-g4986cc3e1b75-dirty #250
[    3.577310] Hardware name: NXP i.MX95 19X19 board (DT)
[    3.582452] Workqueue: events_unbound deferred_probe_work_func
[    3.588291] pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[    3.595233] pc : __virt_to_phys+0x68/0x98
[    3.599246] lr : __virt_to_phys+0x68/0x98
[    3.603276] sp : ffff800083603990
[    3.677939] Call trace:
[    3.680393]  __virt_to_phys+0x68/0x98
[    3.684067]  drm_fbdev_dma_helper_fb_probe+0x138/0x238
[    3.689214]  __drm_fb_helper_initial_config_and_unlock+0x2b0/0x4c0
[    3.695385]  drm_fb_helper_initial_config+0x4c/0x68
[    3.700264]  drm_fbdev_dma_client_hotplug+0x8c/0xe0
[    3.705161]  drm_client_register+0x60/0xb0
[    3.709269]  drm_fbdev_dma_setup+0x94/0x148

Additionally, DMA memory is assumed to by contiguous in physical
address space, which is not guaranteed by vmalloc().

Resolve this by checking the module flag drm_leak_fbdev_smem when
DRM allocated the instance of struct fb_info. Fbdev-dma then only
sets smem_start only if required (via FBINFO_HIDE_SMEM_START). Also
guarantee that the framebuffer is not located in vmalloc address
space.

The Linux kernel CVE team has assigned CVE-2024-41094 to this issue.

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

	Issue introduced in 6.4 with commit a51c7663f144 and fixed in 6.6.37 with commit f29fcfbf6067
	Issue introduced in 6.4 with commit a51c7663f144 and fixed in 6.9.8 with commit 00702cfa8432
	Issue introduced in 6.4 with commit a51c7663f144 and fixed in 6.10 with commit d92a7580392a

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-2024-41094
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_fb_helper.c
	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/f29fcfbf6067c0d8c83f84a045da9276c08deac5
	https://git.kernel.org/stable/c/00702cfa8432ac67a72f56de5e1d278ddea2ebde
	https://git.kernel.org/stable/c/d92a7580392ad4681b1d4f9275d00b95375ebe01