Message-ID: <2024122708-CVE-2024-56617-7f21@gregkh>
Date: Fri, 27 Dec 2024 15:51:24 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56617: cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU

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

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

cacheinfo: Allocate memory during CPU hotplug if not done from the primary CPU

Commit

  5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")

adds functionality that architectures can use to optionally allocate and
build cacheinfo early during boot. Commit

  6539cffa9495 ("cacheinfo: Add arch specific early level initializer")

lets secondary CPUs correct (and reallocate memory) cacheinfo data if
needed.

If the early build functionality is not used and cacheinfo does not need
correction, memory for cacheinfo is never allocated. x86 does not use
the early build functionality. Consequently, during the cacheinfo CPU
hotplug callback, last_level_cache_is_valid() attempts to dereference
a NULL pointer:

  BUG: kernel NULL pointer dereference, address: 0000000000000100
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEPMT SMP NOPTI
  CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
  RIP: 0010: last_level_cache_is_valid+0x95/0xe0a

Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback
if not done earlier.

Moreover, before determining the validity of the last-level cache info,
ensure that it has been allocated. Simply checking for non-zero
cache_leaves() is not sufficient, as some architectures (e.g., Intel
processors) have non-zero cache_leaves() before allocation.

Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
This function iterates over all online CPUs. However, a CPU may have come
online recently, but its cacheinfo may not have been allocated yet.

While here, remove an unnecessary indentation in allocate_cache_info().

  [ bp: Massage. ]

The Linux kernel CVE team has assigned CVE-2024-56617 to this issue.


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

	Issue introduced in 6.4 with commit 6539cffa94957241c096099a57d05fa4d8c7db8a and fixed in 6.6.66 with commit 23b5908b11b77ff8d7b8f7b8f11cbab2e1f4bfc2
	Issue introduced in 6.4 with commit 6539cffa94957241c096099a57d05fa4d8c7db8a and fixed in 6.12.5 with commit 95e197354e0de07e9a20819bdae6562e4dda0f20
	Issue introduced in 6.4 with commit 6539cffa94957241c096099a57d05fa4d8c7db8a and fixed in 6.13-rc2 with commit b3fce429a1e030b50c1c91351d69b8667eef627b

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-2024-56617
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/base/cacheinfo.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/23b5908b11b77ff8d7b8f7b8f11cbab2e1f4bfc2
	https://git.kernel.org/stable/c/95e197354e0de07e9a20819bdae6562e4dda0f20
	https://git.kernel.org/stable/c/b3fce429a1e030b50c1c91351d69b8667eef627b

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