Subject: [syzbot] linux-next boot error: BUG: unable to handle kernel paging request in kernel_execve

From: syzbot <[email-masked]>
Date: Thu, 11 Aug 2022 00:29:34 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    bc6c6584ffb2 Add linux-next specific files for 20220810
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=115034c3080000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5784be4315a4403b
dashboard link: https://syzkaller.appspot.com/bug?extid=3250d9c8925ef29e975f
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

BUG: unable to handle page fault for address: ffffdc0000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 11826067 P4D 11826067 PUD 0 
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 1100 Comm: kworker/u4:5 Not tainted 5.19.0-next-20220810-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
RIP: 0010:strnlen+0x3b/0x70 lib/string.c:504
Code: 74 3c 48 bb 00 00 00 00 00 fc ff df 49 89 fc 48 89 f8 eb 09 48 83 c0 01 48 39 e8 74 1e 48 89 c2 48 89 c1 48 c1 ea 03 83 e1 07 <0f> b6 14 1a 38 ca 7f 04 84 d2 75 11 80 38 00 75 d9 4c 29 e0 48 83
RSP: 0000:ffffc90005c5fe10 EFLAGS: 00010246
RAX: ffff000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 1fffe00000000000 RSI: 0000000000020000 RDI: ffff000000000000
RBP: ffff000000020000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000006 R11: 0000000000000000 R12: ffff000000000000
R13: ffff88814764cc00 R14: ffff000000000000 R15: ffff88814764cc00
FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffdc0000000000 CR3: 000000000bc8e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 strnlen include/linux/fortify-string.h:119 [inline]
 copy_string_kernel+0x26/0x250 fs/exec.c:616
 copy_strings_kernel+0xb3/0x190 fs/exec.c:655
 kernel_execve+0x377/0x500 fs/exec.c:1998
 call_usermodehelper_exec_async+0x2e3/0x580 kernel/umh.c:112
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
 </TASK>
Modules linked in:
CR2: ffffdc0000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:strnlen+0x3b/0x70 lib/string.c:504
Code: 74 3c 48 bb 00 00 00 00 00 fc ff df 49 89 fc 48 89 f8 eb 09 48 83 c0 01 48 39 e8 74 1e 48 89 c2 48 89 c1 48 c1 ea 03 83 e1 07 <0f> b6 14 1a 38 ca 7f 04 84 d2 75 11 80 38 00 75 d9 4c 29 e0 48 83
RSP: 0000:ffffc90005c5fe10 EFLAGS: 00010246
RAX: ffff000000000000 RBX: dffffc0000000000 RCX: 0000000000000000
RDX: 1fffe00000000000 RSI: 0000000000020000 RDI: ffff000000000000
RBP: ffff000000020000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000006 R11: 0000000000000000 R12: ffff000000000000
R13: ffff88814764cc00 R14: ffff000000000000 R15: ffff88814764cc00
FS:  0000000000000000(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffdc0000000000 CR3: 000000000bc8e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	74 3c                	je     0x3e
   2:	48 bb 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbx
   9:	fc ff df
   c:	49 89 fc             	mov    %rdi,%r12
   f:	48 89 f8             	mov    %rdi,%rax
  12:	eb 09                	jmp    0x1d
  14:	48 83 c0 01          	add    $0x1,%rax
  18:	48 39 e8             	cmp    %rbp,%rax
  1b:	74 1e                	je     0x3b
  1d:	48 89 c2             	mov    %rax,%rdx
  20:	48 89 c1             	mov    %rax,%rcx
  23:	48 c1 ea 03          	shr    $0x3,%rdx
  27:	83 e1 07             	and    $0x7,%ecx
* 2a:	0f b6 14 1a          	movzbl (%rdx,%rbx,1),%edx <-- trapping instruction
  2e:	38 ca                	cmp    %cl,%dl
  30:	7f 04                	jg     0x36
  32:	84 d2                	test   %dl,%dl
  34:	75 11                	jne    0x47
  36:	80 38 00             	cmpb   $0x0,(%rax)
  39:	75 d9                	jne    0x14
  3b:	4c 29 e0             	sub    %r12,%rax
  3e:	48                   	rex.W
  3f:	83                   	.byte 0x83

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