linux-cve-announce - CVE-2025-71109: MIPS: ftrace: Fix memory corruption when kernel is located beyond 32 bits

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Message-ID: <2026011412-CVE-2025-71109-f2d9@gregkh>
Date: Wed, 14 Jan 2026 16:06:14 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71109: MIPS: ftrace: Fix memory corruption when kernel is located beyond 32 bits

From: Greg Kroah-Hartman <gregkh@...nel.org>

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

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

MIPS: ftrace: Fix memory corruption when kernel is located beyond 32 bits

Since commit e424054000878 ("MIPS: Tracing: Reduce the overhead of
dynamic Function Tracer"), the macro UASM_i_LA_mostly has been used,
and this macro can generate more than 2 instructions. At the same
time, the code in ftrace assumes that no more than 2 instructions can
be generated, which is why it stores them in an int[2] array. However,
as previously noted, the macro UASM_i_LA_mostly (and now UASM_i_LA)
causes a buffer overflow when _mcount is beyond 32 bits. This leads to
corruption of the variables located in the __read_mostly section.

This corruption was observed because the variable
__cpu_primary_thread_mask was corrupted, causing a hang very early
during boot.

This fix prevents the corruption by avoiding the generation of
instructions if they could exceed 2 instructions in
length. Fortunately, insn_la_mcount is only used if the instrumented
code is located outside the kernel code section, so dynamic ftrace can
still be used, albeit in a more limited scope. This is still
preferable to corrupting memory and/or crashing the kernel.

The Linux kernel CVE team has assigned CVE-2025-71109 to this issue.

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

	Fixed in 6.12.64 with commit e3e33ac2eb69d595079a1a1e444c2fb98efdd42d
	Fixed in 6.18.3 with commit 7f39b9d0e86ed6236b9a5fb67616ab1f76c4f150
	Fixed in 6.19-rc1 with commit 36dac9a3dda1f2bae343191bc16b910c603cac25

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-2025-71109
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/mips/kernel/ftrace.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/e3e33ac2eb69d595079a1a1e444c2fb98efdd42d
	https://git.kernel.org/stable/c/7f39b9d0e86ed6236b9a5fb67616ab1f76c4f150
	https://git.kernel.org/stable/c/36dac9a3dda1f2bae343191bc16b910c603cac25