Subject: CVE-2022-48769: efi: runtime: avoid EFIv2 runtime services on Apple x86 machines

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

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

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

efi: runtime: avoid EFIv2 runtime services on Apple x86 machines

Aditya reports [0] that his recent MacbookPro crashes in the firmware
when using the variable services at runtime. The culprit appears to be a
call to QueryVariableInfo(), which we did not use to call on Apple x86
machines in the past as they only upgraded from EFI v1.10 to EFI v2.40
firmware fairly recently, and QueryVariableInfo() (along with
UpdateCapsule() et al) was added in EFI v2.00.

The only runtime service introduced in EFI v2.00 that we actually use in
Linux is QueryVariableInfo(), as the capsule based ones are optional,
generally not used at runtime (all the LVFS/fwupd firmware update
infrastructure uses helper EFI programs that invoke capsule update at
boot time, not runtime), and not implemented by Apple machines in the
first place. QueryVariableInfo() is used to 'safely' set variables,
i.e., only when there is enough space. This prevents machines with buggy
firmwares from corrupting their NVRAMs when they run out of space.

Given that Apple machines have been using EFI v1.10 services only for
the longest time (the EFI v2.0 spec was released in 2006, and Linux
support for the newly introduced runtime services was added in 2011, but
the MacbookPro12,1 released in 2015 still claims to be EFI v1.10 only),
let's avoid the EFI v2.0 ones on all Apple x86 machines.

[0] https://lore.kernel.org/all/[email-masked]/

The Linux kernel CVE team has assigned CVE-2022-48769 to this issue.

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

	Fixed in 5.10.96 with commit b0f1cc093bc2
	Fixed in 5.15.19 with commit 3df524489788
	Fixed in 5.16.5 with commit a4085859411c
	Fixed in 5.17 with commit f5390cd0b43c

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-2022-48769
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/efi/efi.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/b0f1cc093bc2493ac259c53766fd2b800e085807
	https://git.kernel.org/stable/c/3df52448978802ae15dcebf66beba1029df957b4
	https://git.kernel.org/stable/c/a4085859411c825c321c9b55b8a9dc5a128a6684
	https://git.kernel.org/stable/c/f5390cd0b43c2e54c7cf5506c7da4a37c5cef746