linux-kernel - [Bug] WARNING in static_key_disable

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Date: Tue, 5 Mar 2024 15:54:24 +0800
From: Sam Sun <samsun1006219@...il.com>
To: linux-kernel@...r.kernel.org
Cc: syzkaller@...glegroups.com, xrivendell7@...il.com, ardb@...nel.org, 
	rostedt@...dmis.org, jbaron@...mai.com, jpoimboe@...nel.org, 
	peterz@...radead.org, linux-mm@...ck.org, akpm@...ux-foundation.org
Subject: [Bug] WARNING in static_key_disable_cpuslocked

Dear developers and maintainers,

We encountered a kernel warning while using our modified Syzkaller. It
is tested against linux kernel 6.8-rc7. Kernel config and C repro are
attached to this email. The kernel log is listed below.

```
WARNING: CPU: 0 PID: 8286 at kernel/jump_label.c:229
static_key_disable_cpuslocked+0x15e/0x1c0 kernel/jump_label.c:229
Modules linked in:
CPU: 0 PID: 8286 Comm: syz-executor393 Not tainted 6.7.0-rc7 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:static_key_disable_cpuslocked+0x15e/0x1c0 kernel/jump_label.c:229
Code: d3 ff 48 c7 c7 a0 cc 0a 8d e8 5e d3 b6 08 5b 5d e9 f7 bd d3 ff
e8 f2 bd d3 ff 48 89 ef e8 2a f8 ff ff eb d9 e8 e3 bd d3 ff 90 <0f> 0b
90 eb 8f e8 d8 bd d3 ff 90 48 c7 c6 00 74 b7 8a 48 89 ea 48
RSP: 0018:ffffc90002c4faf0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff81b1568e
RDX: ffff888013b5d980 RSI: ffffffff81b156fd RDI: 0000000000000005
RBP: ffffffff8d0c75d0 R08: 0000000000000005 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffff8d0c75d0
R13: ffff8880209fb980 R14: 0000000000000000 R15: ffffffff8211e160
FS:  0000555555e0e3c0(0000) GS:ffff888063a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f49e210e090 CR3: 000000001a2d4000 CR4: 0000000000750ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 <TASK>
 static_key_disable+0x1a/0x20 kernel/jump_label.c:243
 enabled_store+0x288/0x2040 mm/vmscan.c:5137
 kobj_attr_store+0x54/0x80 lib/kobject.c:836
 sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136
 kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334
 call_write_iter include/linux/fs.h:2020 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x96a/0xd80 fs/read_write.c:584
 ksys_write+0x122/0x250 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f49e208a7bd
Code: c3 e8 a7 1f 00 00 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe25660128 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f49e20db078 RCX: 00007f49e208a7bd
RDX: 0000000000000002 RSI: 0000000020000080 RDI: 0000000000000004
RBP: 0000000000000000 R08: 00007f49e20dfb55 R09: 00007f49e20dfb55
R10: 00007f49e20dfb55 R11: 0000000000000246 R12: 00000000000207f3
R13: 00007ffe2566013c R14: 00007ffe25660150 R15: 00007ffe25660140
 </TASK>
```

We analyzed the cause of this bug. It seems that in function
static_key_disable_cpuslocked(), there is a small racing window
between two atomic_read(&key->enabled) in line 228 & 229, triggering
the WARN_ON_ONCE macro. This might cause function returned without
actually disabling the static_key "key". I am not sure if there is any
other potential threat here.

I searched on web and found that there was a similar bug reported by
syzbot several years ago
(https://groups.google.com/g/syzkaller-bugs/c/_W3lgRCwlb4/m/TqzyQcPpAQAJ).
At that time the fix was in the net instead of kernel/jump_label.c. So
I checked the call stack and cc this email to memory management
maintainers. Hope there is no confusion.

If you have any questions, please contact us.
Reported by: Yue Sun <samsun1006219@...il.com>
Reported by: xingwei lee <xrivendell7@...il.com>

Best Regards,
Yue

Download attachment "config" of type "application/octet-stream" (246595 bytes)

View attachment "static_key_disable_cpuslocked.c" of type "text/x-csrc" (4054 bytes)