linux-cve-announce - CVE-2023-54278: s390/vmem: split pages when debug pagealloc is enabled

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Message-ID: <2025123003-CVE-2023-54278-d4b2@gregkh>
Date: Tue, 30 Dec 2025 13:20:44 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-54278: s390/vmem: split pages when debug pagealloc is enabled

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

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

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

s390/vmem: split pages when debug pagealloc is enabled

Since commit bb1520d581a3 ("s390/mm: start kernel with DAT enabled")
the kernel crashes early during boot when debug pagealloc is enabled:

mem auto-init: stack:off, heap alloc:off, heap free:off
addressing exception: 0005 ilc:2 [#1] SMP DEBUG_PAGEALLOC
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 6.5.0-rc3-09759-gc5666c912155 #630
[..]
Krnl Code: 00000000001325f6: ec5600248064 cgrj %r5,%r6,8,000000000013263e
           00000000001325fc: eb880002000c srlg %r8,%r8,2
          #0000000000132602: b2210051     ipte %r5,%r1,%r0,0
          >0000000000132606: b90400d1     lgr %r13,%r1
           000000000013260a: 41605008     la %r6,8(%r5)
           000000000013260e: a7db1000     aghi %r13,4096
           0000000000132612: b221006d     ipte %r6,%r13,%r0,0
           0000000000132616: e3d0d0000171 lay %r13,4096(%r13)

Call Trace:
 __kernel_map_pages+0x14e/0x320
 __free_pages_ok+0x23a/0x5a8)
 free_low_memory_core_early+0x214/0x2c8
 memblock_free_all+0x28/0x58
 mem_init+0xb6/0x228
 mm_core_init+0xb6/0x3b0
 start_kernel+0x1d2/0x5a8
 startup_continue+0x36/0x40
Kernel panic - not syncing: Fatal exception: panic_on_oops

This is caused by using large mappings on machines with EDAT1/EDAT2. Add
the code to split the mappings into 4k pages if debug pagealloc is enabled
by CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc kernel
command line option.

The Linux kernel CVE team has assigned CVE-2023-54278 to this issue.


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

	Issue introduced in 6.3 with commit bb1520d581a3a46e2d6e12bb74604ace33404de5 and fixed in 6.4.10 with commit 601e467e29a960f7ab7ec4075afc6a68c3532a65
	Issue introduced in 6.3 with commit bb1520d581a3a46e2d6e12bb74604ace33404de5 and fixed in 6.5 with commit edc1e4b6e26536868ef819a735e04a5b32c10589

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-2023-54278
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/s390/mm/vmem.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/601e467e29a960f7ab7ec4075afc6a68c3532a65
	https://git.kernel.org/stable/c/edc1e4b6e26536868ef819a735e04a5b32c10589