CVE-2026-53343: ARM: 9475/1: entry: use byte load for KASAN VMAP stack shadow

CVE-2026-53343: ARM: 9475/1: entry: use byte load for KASAN VMAP stack shadow

[Greg Kroah-Hartman]

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

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

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

ARM: 9475/1: entry: use byte load for KASAN VMAP stack shadow

Commit 44e9a3bb76e5 ("ARM: 9430/1: entry: Do a dummy read from
VMAP shadow") added a dummy read from the KASAN VMAP stack shadow in
__switch_to(). The read uses ldr, but the KASAN shadow address is
byte-granular and is not guaranteed to be word aligned.

ARMv5 faults unaligned word loads. With CONFIG_KASAN_VMALLOC and
CONFIG_VMAP_STACK enabled, ARM926/VersatilePB crashes in __switch_to()
with an alignment exception before reaching init.

Use ldrb for the dummy shadow access. The code only needs to fault in the
shadow mapping if the stack shadow is missing, so a byte load is sufficient
and matches the granularity of KASAN shadow memory.

The Linux kernel CVE team has assigned CVE-2026-53343 to this issue.


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

	Issue introduced in 6.1.120 with commit 8fe148d39c127de3fb78dfa6da95a3608dfda454 and fixed in 6.1.176 with commit c0b8c148a7754826156993ed6442d31536ec86b4
	Issue introduced in 6.6.64 with commit ef21187c0672a2b2cbec44f33bab9ec47d5c277c and fixed in 6.6.143 with commit c2e3aadc8fef7da068490597fc5582f8f362aeb2
	Issue introduced in 6.12.4 with commit c86d26b4b089ca294b3b7d915a7da61edb77935f and fixed in 6.12.94 with commit c74990828d3c486ee44aaa68240eb3abff289d1c
	Issue introduced in 6.13 with commit 44e9a3bb76e5f2eecd374c8176b2c5163c8bb2e2 and fixed in 6.18.36 with commit 517720913bd3c17a52cd55a740064f68455ab88e
	Issue introduced in 6.13 with commit 44e9a3bb76e5f2eecd374c8176b2c5163c8bb2e2 and fixed in 7.0.13 with commit 2a4dc9a0ac3326e79fb58fdaae724b92127709a9
	Issue introduced in 6.13 with commit 44e9a3bb76e5f2eecd374c8176b2c5163c8bb2e2 and fixed in 7.1 with commit 77a1f6883dc6e837bb2cb30b9b02e2f94338e2c6

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-2026-53343
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/arm/kernel/entry-armv.S


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/c0b8c148a7754826156993ed6442d31536ec86b4
	https://git.kernel.org/stable/c/c2e3aadc8fef7da068490597fc5582f8f362aeb2
	https://git.kernel.org/stable/c/c74990828d3c486ee44aaa68240eb3abff289d1c
	https://git.kernel.org/stable/c/517720913bd3c17a52cd55a740064f68455ab88e
	https://git.kernel.org/stable/c/2a4dc9a0ac3326e79fb58fdaae724b92127709a9
	https://git.kernel.org/stable/c/77a1f6883dc6e837bb2cb30b9b02e2f94338e2c6