Subject: CVE-2023-52504: x86/alternatives: Disable KASAN in apply_alternatives()

From: Greg Kroah-Hartman <[email-masked]>

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

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

x86/alternatives: Disable KASAN in apply_alternatives()

Fei has reported that KASAN triggers during apply_alternatives() on
a 5-level paging machine:

	BUG: KASAN: out-of-bounds in rcu_is_watching()
	Read of size 4 at addr ff110003ee6419a0 by task swapper/0/0
	...
	__asan_load4()
	rcu_is_watching()
	trace_hardirqs_on()
	text_poke_early()
	apply_alternatives()
	...

On machines with 5-level paging, cpu_feature_enabled(X86_FEATURE_LA57)
gets patched. It includes KASAN code, where KASAN_SHADOW_START depends on
__VIRTUAL_MASK_SHIFT, which is defined with cpu_feature_enabled().

KASAN gets confused when apply_alternatives() patches the
KASAN_SHADOW_START users. A test patch that makes KASAN_SHADOW_START
static, by replacing __VIRTUAL_MASK_SHIFT with 56, works around the issue.

Fix it for real by disabling KASAN while the kernel is patching alternatives.

[ mingo: updated the changelog ]

The Linux kernel CVE team has assigned CVE-2023-52504 to this issue.

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

	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 4.19.297 with commit 3719d3c36aa8
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 5.4.270 with commit 3770c38cd6a6
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 5.10.199 with commit 6788b10620ca
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 5.15.136 with commit ecba5afe86f3
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 6.1.59 with commit 5b784489c815
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 6.5.8 with commit cd287cc208df
	Issue introduced in 4.17 with commit 6657fca06e3f and fixed in 6.6 with commit d35652a5fc99

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-2023-52504
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/x86/kernel/alternative.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/3719d3c36aa853d5a2401af9f8d6b116c91ad5ae
	https://git.kernel.org/stable/c/3770c38cd6a60494da29ac2da73ff8156440a2d1
	https://git.kernel.org/stable/c/6788b10620ca6e98575d1e06e72a8974aad7657e
	https://git.kernel.org/stable/c/ecba5afe86f30605eb9dfb7f265a8de0218d4cfc
	https://git.kernel.org/stable/c/5b784489c8158518bf7a466bb3cc045b0fb66b4b
	https://git.kernel.org/stable/c/cd287cc208dfe6bd6da98e7f88e723209242c9b4
	https://git.kernel.org/stable/c/d35652a5fc9944784f6f50a5c979518ff8dacf61