[moderation] [mm?] general protection fault in ksm_do_scan

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3ffea9a7a6f7 Merge tag 'smp_urgent_for_v6.10_rc6' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16ada0be980000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f6afbd1f6b11509
dashboard link: https://syzkaller.appspot.com/bug?extid=a80d44d3b2f47462bd2b
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linu...@kvack.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f041d7c8c4f4/disk-3ffea9a7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1dad47f107fc/vmlinux-3ffea9a7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d734b3aca51b/bzImage-3ffea9a7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a80d44...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000084: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000420-0x0000000000000427]
CPU: 1 PID: 36 Comm: ksmd Not tainted 6.10.0-rc5-syzkaller-00294-g3ffea9a7a6f7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
RIP: 0010:scan_get_next_rmap_item mm/ksm.c:2647 [inline]
RIP: 0010:ksm_do_scan+0x79c/0x6860 mm/ksm.c:2759
Code: 89 e7 48 c7 c6 ff ff ff ff e8 f0 66 80 09 49 89 c6 48 85 c0 4c 89 7c 24 60 0f 84 b9 0a 00 00 49 8d 5e 20 48 89 d8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 df e8 d5 5e 01 00 48 8b 1b be 00 00 00
RSP: 0018:ffffc90000ac7b40 EFLAGS: 00010207
RAX: 0000000000000084 RBX: 0000000000000426 RCX: ffff88801b2ada00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90000ac7d90 R08: ffffffff8b7abdb4 R09: ffffffff8b7abc39
R10: 0000000000000004 R11: ffff88801b2ada00 R12: ffffc90000ac7ce0
R13: dffffc0000000000 R14: 0000000000000406 R15: ffff88807c7ca6c4
FS: 0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbd3b95bd58 CR3: 000000000e132000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
ksm_scan_thread+0x110/0x490 mm/ksm.c:2784
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
Modules linked in:
----------------
Code disassembly (best guess):
0: 89 e7 mov %esp,%edi
2: 48 c7 c6 ff ff ff ff mov $0xffffffffffffffff,%rsi
9: e8 f0 66 80 09 call 0x98066fe
e: 49 89 c6 mov %rax,%r14
11: 48 85 c0 test %rax,%rax
14: 4c 89 7c 24 60 mov %r15,0x60(%rsp)
19: 0f 84 b9 0a 00 00 je 0xad8
1f: 49 8d 5e 20 lea 0x20(%r14),%rbx
23: 48 89 d8 mov %rbx,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 48 89 df mov %rbx,%rdi
34: e8 d5 5e 01 00 call 0x15f0e
39: 48 8b 1b mov (%rbx),%rbx
3c: be .byte 0xbe
3d: 00 00 add %al,(%rax)


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