CVE-2026-68400: firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation

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

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

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

firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation

Use the descriptor's `ep_mem_offset` to calculate the start of the endpoint
memory access array and to comply with the FF-A spec instead of defaulting
to `sizeof(struct ffa_mem_region)`.
This requires moving `ffa_mem_region_additional_setup()` earlier in the setup
flow.
Also, add sanity checks to ensure the calculated descriptor offsets do not
exceed `max_fragsize`.

The Linux kernel CVE team has assigned CVE-2026-68400 to this issue.


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

	Issue introduced in 6.7 with commit 113580530ee7dc61e668b641d657920734533b9f and fixed in 6.18.42 with commit b39b08e6bee812514b449dc874076890e6b871a0
	Issue introduced in 6.7 with commit 113580530ee7dc61e668b641d657920734533b9f and fixed in 7.1.6 with commit 8ef18f0ab3c0ec1eac77289f5a542bd96a8a6d66
	Issue introduced in 6.7 with commit 113580530ee7dc61e668b641d657920734533b9f and fixed in 7.2-rc4 with commit b4d961351aa84fdf0148783fb1f3a1391b8a0adb

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-2026-68400
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/firmware/arm_ffa/driver.c
	include/linux/arm_ffa.h


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/b39b08e6bee812514b449dc874076890e6b871a0
	https://git.kernel.org/stable/c/8ef18f0ab3c0ec1eac77289f5a542bd96a8a6d66
	https://git.kernel.org/stable/c/b4d961351aa84fdf0148783fb1f3a1391b8a0adb