Happy new year! On Tue, Dec 31, 2024 at 08:50:23PM -0800, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 8379578b11d5 Merge tag 'for-v6.13-rc' of git://git.kernel... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=16113018580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=d269ef41b9262400 > dashboard link: https://syzkaller.appspot.com/bug?extid=46423ed8fa1f1148c6e4 > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > userspace arch: i386 Hmmmm 32-bit? But kernel reports give 64-bit registers? So I guess 32-bit userland, 64-bit kernel? > > Unfortunately, I don't have any reproducer for this issue yet. Hmm. Racey thing? > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/86d2e3352aff/disk-8379578b.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/345570cd3573/vmlinux-8379578b.xz > kernel image: https://storage.googleapis.com/syzbot-assets/01da37a51505/bzImage-8379578b.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+46423ed8fa1f1148c6e4@xxxxxxxxxxxxxxxxxxxxxxxxx > > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > </TASK> > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 20504 at mm/vma.c:734 vma_merge_existing_range+0x1145/0x16f0 mm/vma.c:734 It'd be nice if syzbot could actually print the code that generates the warning :) a nice-to-have perhaps. This is: VM_WARN_ON(start >= end); I suspect start == end, because start > end would be some drastic and god-awful bug. > Modules linked in: > CPU: 1 UID: 0 PID: 20504 Comm: syz.6.5485 Not tainted 6.13.0-rc4-syzkaller-00069-g8379578b11d5 #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 > RIP: 0010:vma_merge_existing_range+0x1145/0x16f0 mm/vma.c:734 > Code: e8 20 24 0f 00 4d 2b 7d 00 4d 89 ec 48 8b 7c 24 38 e9 7f 01 00 00 e8 3a bc a8 ff 90 0f 0b 90 e9 a8 f1 ff ff e8 2c bc a8 ff 90 <0f> 0b 90 e9 0e f2 ff ff e8 1e bc a8 ff 90 0f 0b 90 4d 85 ed 0f 85 Be useful to get the kernel disassembly too :) Best guess wranging a python script and objdump: 0: e8 20 24 0f 00 call 0xf2425 5: 4d 2b 7d 00 sub 0x0(%r13),%r15 9: 4d 89 ec mov %r13,%r12 c: 48 8b 7c 24 38 mov 0x38(%rsp),%rdi 11: e9 7f 01 00 00 jmp 0x195 16: e8 3a bc a8 ff call 0xffffffffffa8bc55 1b: 90 nop 1c: 0f 0b ud2 1e: 90 nop 1f: e9 a8 f1 ff ff jmp 0xfffffffffffff1cc 24: e8 2c bc a8 ff call 0xffffffffffa8bc55 29: 90 nop 2a: <0f> 0b ud2 <-- presumably here? This is an undefined instruction... 2c: 90 nop 2d: e9 0e f2 ff ff jmp 0xfffffffffffff240 32: e8 1e bc a8 ff call 0xffffffffffa8bc55 37: 90 nop 38: 0f 0b ud2 3a: 90 nop 3b: 4d 85 ed test %r13,%r13 3e: 0f .byte 0xf 3f: 85 .byte 0x85 Yeah this might be a mix of data and code somehow or just garbage? Not sure there's anything discernable there unfortunately. > RSP: 0018:ffffc9000ba274a0 EFLAGS: 00010293 > RAX: ffffffff81f6b804 RBX: 0000000020c25000 RCX: ffff888060ad1e00 > RDX: 0000000000000000 RSI: 0000000020c25000 RDI: 0000000020c25000 > RBP: ffffc9000ba275f8 R08: ffffffff81f6aa0d R09: 00000000280000fa > R10: ffffc9000ba27810 R11: fffff52001744f07 R12: 0000000020c25000 > R13: ffff888069b666c8 R14: ffffc9000ba276a0 R15: ffff888068d0b1f0 > FS: 0000000000000000(0000) GS:ffff8880b8700000(0063) knlGS:00000000f5116b40 > CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033 > CR2: 00007fa9de2c0018 CR3: 000000006b562000 CR4: 00000000003526f0 > Call Trace: > <TASK> > vma_modify+0x41/0x330 mm/vma.c:1514 Just passes through start, end (in vmg). > vma_modify_flags_name+0x3a6/0x430 mm/vma.c:1563 Just passes through start, end. > madvise_update_vma+0x2fe/0xc10 mm/madvise.c:159 Just passes through start, end. This means it was one of MADV_NORMAL, MADV_RANDOM, MADV_DONTFORK, MADV_DOFORK, MADV_WIPEONFORK, MADV_KEEPONFORK, MADV_DONTDUMP, MADV_DODUMP, MADV_MERGEABLE, MADV_UNMERGEABLE, MADV_HUGEPAGE, MADV_NOHUGEPAGE. Yeah we need better error handling here, because this report is just giving us very little to go on especially for a non-repro. Will add to TODO. > madvise_vma_behavior mm/madvise.c:1325 [inline] Just passes through start, end. > madvise_walk_vmas mm/madvise.c:1497 [inline] OK here we find VMAs and walk them. We explicitly check for start >= send if start < vma->vm_start. I wonder if the visit() call is splitting the VMA which confuses the logic here. s e | | v v |-------------| | | |-------------| Split: s e | | v v |--------|----| | | | |--------|----| prev = this VMA. if (prev && start < prev->vm_end) start = prev->vm_end; So we end up with: s,e | v |--------|----| | | | |--------|----| tmp = vma->vm_end; if (end < tmp) tmp = end; That tmp assignment will reinstate the broken end And... boom. Let me check this out and see if I can trigger it. I may be missing some safeguard that prevents this... > do_madvise+0x1e64/0x4d10 mm/madvise.c:1684 Here we explicitly check for start >= end: end = start + len; if (end < start) return -EINVAL; if (end == start) return 0; So overflow is accounted for also. But since this is a 64-bit kernel not really a concern. > __do_sys_madvise mm/madvise.c:1700 [inline] > __se_sys_madvise mm/madvise.c:1698 [inline] > __ia32_sys_madvise+0xa6/0xc0 mm/madvise.c:1698 > do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline] > __do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386 > do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411 > entry_SYSENTER_compat_after_hwframe+0x84/0x8e > RIP: 0023:0xf7fc2579 > Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 > RSP: 002b:00000000f511655c EFLAGS: 00000206 ORIG_RAX: 00000000000000db > RAX: ffffffffffffffda RBX: 0000000020c00000 RCX: 0000000000400000 > RDX: 000000000000000e RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > </TASK> > ---------------- > Code disassembly (best guess), 2 bytes skipped: > 0: 10 06 adc %al,(%rsi) > 2: 03 74 b4 01 add 0x1(%rsp,%rsi,4),%esi > 6: 10 07 adc %al,(%rdi) > 8: 03 74 b0 01 add 0x1(%rax,%rsi,4),%esi > c: 10 08 adc %cl,(%rax) > e: 03 74 d8 01 add 0x1(%rax,%rbx,8),%esi > 1e: 00 51 52 add %dl,0x52(%rcx) > 21: 55 push %rbp > 22: 89 e5 mov %esp,%ebp > 24: 0f 34 sysenter > 26: cd 80 int $0x80 > * 28: 5d pop %rbp <-- trapping instruction > 29: 5a pop %rdx > 2a: 59 pop %rcx > 2b: c3 ret > 2c: 90 nop > 2d: 90 nop > 2e: 90 nop > 2f: 90 nop > 30: 90 nop > 31: 90 nop > 32: 90 nop > 33: 90 nop > 34: 90 nop > 35: 90 nop > 36: 90 nop > 37: 90 nop > 38: 90 nop > 39: 90 nop > 3a: 90 nop > 3b: 90 nop > 3c: 90 nop > 3d: 90 nop > > > --- > This report is generated by a bot. It may contain errors. > See https://goo.gl/tpsmEJ for more information about syzbot. > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > If the report is already addressed, let syzbot know by replying with: > #syz fix: exact-commit-title > > If you want to overwrite report's subsystems, reply with: > #syz set subsystems: new-subsystem > (See the list of subsystem names on the web dashboard) > > If the report is a duplicate of another one, reply with: > #syz dup: exact-subject-of-another-report > > If you want to undo deduplication, reply with: > #syz undup
