Subject: CVE-2024-35872: mm/secretmem: fix GUP-fast succeeding on secretmem folios

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

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

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

mm/secretmem: fix GUP-fast succeeding on secretmem folios

folio_is_secretmem() currently relies on secretmem folios being LRU
folios, to save some cycles.

However, folios might reside in a folio batch without the LRU flag set, or
temporarily have their LRU flag cleared.  Consequently, the LRU flag is
unreliable for this purpose.

In particular, this is the case when secretmem_fault() allocates a fresh
page and calls filemap_add_folio()->folio_add_lru().  The folio might be
added to the per-cpu folio batch and won't get the LRU flag set until the
batch was drained using e.g., lru_add_drain().

Consequently, folio_is_secretmem() might not detect secretmem folios and
GUP-fast can succeed in grabbing a secretmem folio, crashing the kernel
when we would later try reading/writing to the folio, because the folio
has been unmapped from the directmap.

Fix it by removing that unreliable check.

The Linux kernel CVE team has assigned CVE-2024-35872 to this issue.

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

	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 5.15.154 with commit 6564b014af92
	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 6.1.85 with commit 9c2b4b657739
	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 6.6.26 with commit 43fad1d0284d
	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 6.8.5 with commit 201e4aaf405d
	Issue introduced in 5.14 with commit 1507f51255c9 and fixed in 6.9 with commit 65291dcfcf89

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-2024-35872
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:
	include/linux/secretmem.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/6564b014af92b677c1f07c44d7f5b595d589cf6e
	https://git.kernel.org/stable/c/9c2b4b657739ecda38e3b383354a29566955ac48
	https://git.kernel.org/stable/c/43fad1d0284de30159661d0badfc3cbaf7e6f8f8
	https://git.kernel.org/stable/c/201e4aaf405dfd1308da54448654053004c579b5
	https://git.kernel.org/stable/c/65291dcfcf8936e1b23cfd7718fdfde7cfaf7706