Subject: CVE-2024-49935: ACPI: PAD: fix crash in exit_round_robin()

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

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

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

ACPI: PAD: fix crash in exit_round_robin()

The kernel occasionally crashes in cpumask_clear_cpu(), which is called
within exit_round_robin(), because when executing clear_bit(nr, addr) with
nr set to 0xffffffff, the address calculation may cause misalignment within
the memory, leading to access to an invalid memory address.

----------
BUG: unable to handle kernel paging request at ffffffffe0740618
        ...
CPU: 3 PID: 2919323 Comm: acpi_pad/14 Kdump: loaded Tainted: G           OE  X --------- -  - 4.18.0-425.19.2.el8_7.x86_64 #1
        ...
RIP: 0010:power_saving_thread+0x313/0x411 [acpi_pad]
Code: 89 cd 48 89 d3 eb d1 48 c7 c7 55 70 72 c0 e8 64 86 b0 e4 c6 05 0d a1 02 00 01 e9 bc fd ff ff 45 89 e4 42 8b 04 a5 20 82 72 c0 <f0> 48 0f b3 05 f4 9c 01 00 42 c7 04 a5 20 82 72 c0 ff ff ff ff 31
RSP: 0018:ff72a5d51fa77ec8 EFLAGS: 00010202
RAX: 00000000ffffffff RBX: ff462981e5d8cb80 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000246 RDI: 0000000000000246
RBP: ff46297556959d80 R08: 0000000000000382 R09: ff46297c8d0f38d8
R10: 0000000000000000 R11: 0000000000000001 R12: 000000000000000e
R13: 0000000000000000 R14: ffffffffffffffff R15: 000000000000000e
FS:  0000000000000000(0000) GS:ff46297a800c0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffe0740618 CR3: 0000007e20410004 CR4: 0000000000771ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 ? acpi_pad_add+0x120/0x120 [acpi_pad]
 kthread+0x10b/0x130
 ? set_kthread_struct+0x50/0x50
 ret_from_fork+0x1f/0x40
        ...
CR2: ffffffffe0740618

crash> dis -lr ffffffffc0726923
        ...
/usr/src/debug/kernel-4.18.0-425.19.2.el8_7/linux-4.18.0-425.19.2.el8_7.x86_64/./include/linux/cpumask.h: 114
0xffffffffc0726918 <power_saving_thread+776>:	mov    %r12d,%r12d
/usr/src/debug/kernel-4.18.0-425.19.2.el8_7/linux-4.18.0-425.19.2.el8_7.x86_64/./include/linux/cpumask.h: 325
0xffffffffc072691b <power_saving_thread+779>:	mov    -0x3f8d7de0(,%r12,4),%eax
/usr/src/debug/kernel-4.18.0-425.19.2.el8_7/linux-4.18.0-425.19.2.el8_7.x86_64/./arch/x86/include/asm/bitops.h: 80
0xffffffffc0726923 <power_saving_thread+787>:	lock btr %rax,0x19cf4(%rip)        # 0xffffffffc0740620 <pad_busy_cpus_bits>

crash> px tsk_in_cpu[14]
$66 = 0xffffffff

crash> px 0xffffffffc072692c+0x19cf4
$99 = 0xffffffffc0740620

crash> sym 0xffffffffc0740620
ffffffffc0740620 (b) pad_busy_cpus_bits [acpi_pad]

crash> px pad_busy_cpus_bits[0]
$42 = 0xfffc0
----------

To fix this, ensure that tsk_in_cpu[tsk_index] != -1 before calling
cpumask_clear_cpu() in exit_round_robin(), just as it is done in
round_robin_cpu().

[ rjw: Subject edit, avoid updates to the same value ]

The Linux kernel CVE team has assigned CVE-2024-49935 to this issue.

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

	Fixed in 5.15.168 with commit 92e5661b7d07
	Fixed in 6.1.113 with commit 68a599da16eb
	Fixed in 6.6.55 with commit 68a8e45743d6
	Fixed in 6.10.14 with commit 03593dbb0b27
	Fixed in 6.11.3 with commit 27c045f868f0
	Fixed in 6.12-rc1 with commit 0a2ed70a549e

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-2024-49935
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:
	drivers/acpi/acpi_pad.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/92e5661b7d0727ab912b76625a88b33fdb9b609a
	https://git.kernel.org/stable/c/68a599da16ebad442ce295d8d2d5c488e3992822
	https://git.kernel.org/stable/c/68a8e45743d6a120f863fb14b72dc59616597019
	https://git.kernel.org/stable/c/03593dbb0b272ef7b0358b099841e65735422aca
	https://git.kernel.org/stable/c/27c045f868f0e5052c6b532868a65e0cd250c8fc
	https://git.kernel.org/stable/c/0a2ed70a549e61c5181bad5db418d223b68ae932