linux-cve-announce - CVE-2025-21851: bpf: Fix softlockup in arena_map

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Message-ID: <2025031213-CVE-2025-21851-87bd@gregkh>
Date: Wed, 12 Mar 2025 10:42:17 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21851: bpf: Fix softlockup in arena_map_free on 64k page kernel

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

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

bpf: Fix softlockup in arena_map_free on 64k page kernel

On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y,
arena_htab tests cause a segmentation fault and soft lockup.
The same failure is not observed with 4k pages on aarch64.

It turns out arena_map_free() is calling
apply_to_existing_page_range() with the address returned by
bpf_arena_get_kern_vm_start().  If this address is not page-aligned
the code ends up calling apply_to_pte_range() with that unaligned
address causing soft lockup.

Fix it by round up GUARD_SZ to PAGE_SIZE << 1 so that the
division by 2 in bpf_arena_get_kern_vm_start() returns
a page-aligned value.

The Linux kernel CVE team has assigned CVE-2025-21851 to this issue.


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

	Issue introduced in 6.9 with commit 317460317a02a1af512697e6e964298dedd8a163 and fixed in 6.12.17 with commit c1f3f3892d4526f18aaeffdb6068ce861e793ee3
	Issue introduced in 6.9 with commit 317460317a02a1af512697e6e964298dedd8a163 and fixed in 6.13.5 with commit 787d556a3de447e70964a4bdeba9196f62a62b1e
	Issue introduced in 6.9 with commit 317460317a02a1af512697e6e964298dedd8a163 and fixed in 6.14-rc4 with commit 517e8a7835e8cfb398a0aeb0133de50e31cae32b

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-2025-21851
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:
	kernel/bpf/arena.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/c1f3f3892d4526f18aaeffdb6068ce861e793ee3
	https://git.kernel.org/stable/c/787d556a3de447e70964a4bdeba9196f62a62b1e
	https://git.kernel.org/stable/c/517e8a7835e8cfb398a0aeb0133de50e31cae32b