Subject: CVE-2024-50017: x86/mm/ident_map: Use gbpages only where full GB page should be mapped.

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

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

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

x86/mm/ident_map: Use gbpages only where full GB page should be mapped.

When ident_pud_init() uses only GB pages to create identity maps, large
ranges of addresses not actually requested can be included in the resulting
table; a 4K request will map a full GB.  This can include a lot of extra
address space past that requested, including areas marked reserved by the
BIOS.  That allows processor speculation into reserved regions, that on UV
systems can cause system halts.

Only use GB pages when map creation requests include the full GB page of
space.  Fall back to using smaller 2M pages when only portions of a GB page
are included in the request.

No attempt is made to coalesce mapping requests. If a request requires a
map entry at the 2M (pmd) level, subsequent mapping requests within the
same 1G region will also be at the pmd level, even if adjacent or
overlapping such requests could have been combined to map a full GB page.
Existing usage starts with larger regions and then adds smaller regions, so
this should not have any great consequence.

The Linux kernel CVE team has assigned CVE-2024-50017 to this issue.

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

	Fixed in 6.10.14 with commit d80a99892f7a
	Fixed in 6.11.3 with commit a23823098ab2
	Fixed in 6.12-rc1 with commit cc31744a2945

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-2024-50017
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:
	arch/x86/mm/ident_map.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/d80a99892f7a992d103138fa4636b2c33abd6740
	https://git.kernel.org/stable/c/a23823098ab2c277c14fc110b97d8d5c83597195
	https://git.kernel.org/stable/c/cc31744a294584a36bf764a0ffa3255a8e69f036