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* [syzbot] [mm?] BUG: unable to handle kernel paging request in move_pages
@ 2025-07-17 19:13 syzbot
  2025-07-28 21:08 ` Peter Xu
  0 siblings, 1 reply; 7+ messages in thread
From: syzbot @ 2025-07-17 19:13 UTC (permalink / raw)
  To: akpm, linux-kernel, linux-mm, peterx, syzkaller-bugs

Hello,

syzbot found the following issue on:

HEAD commit:    e8352908bdcd Add linux-next specific files for 20250716
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17f81382580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b7b0e60e17dc5717
dashboard link: https://syzkaller.appspot.com/bug?extid=b446dbe27035ef6bd6c2
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10041382580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10eb158c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ae8cc81c1781/disk-e8352908.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/57aaea991896/vmlinux-e8352908.xz
kernel image: https://storage.googleapis.com/syzbot-assets/feb871619bd4/bzImage-e8352908.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: ffffea6000391008
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 13fff8067 P4D 13fff8067 PUD 0 
Oops: Oops: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 5860 Comm: syz-executor832 Not tainted 6.16.0-rc6-next-20250716-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
RIP: 0010:move_pages+0xbe6/0x1430 mm/userfaultfd.c:1824
Code: c1 ec 06 4b 8d 1c 2c 48 83 c3 08 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 9a 30 f4 ff <48> 8b 1b 48 89 de 48 83 e6 01 31 ff e8 59 70 8f ff 48 89 d8 48 83
RSP: 0018:ffffc90003f778a8 EFLAGS: 00010246
RAX: 1ffffd4c00072201 RBX: ffffea6000391008 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520007eef00 R12: 0000006000391000
R13: ffffea0000000000 R14: 200018000e4401fd R15: 00002000003ab000
FS:  00007ff35708f6c0(0000) GS:ffff8881258aa000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffea6000391008 CR3: 0000000074390000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 userfaultfd_move fs/userfaultfd.c:1923 [inline]
 userfaultfd_ioctl+0x2e8b/0x4c80 fs/userfaultfd.c:2046
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff3570d6519
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff35708f218 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ff357160308 RCX: 00007ff3570d6519
RDX: 0000200000000180 RSI: 00000000c028aa05 RDI: 0000000000000003
RBP: 00007ff357160300 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff35712d074
R13: 0000200000000180 R14: 0000200000000188 R15: 00002000002b9000
 </TASK>
Modules linked in:
CR2: ffffea6000391008
---[ end trace 0000000000000000 ]---
RIP: 0010:_compound_head include/linux/page-flags.h:284 [inline]
RIP: 0010:move_pages+0xbe6/0x1430 mm/userfaultfd.c:1824
Code: c1 ec 06 4b 8d 1c 2c 48 83 c3 08 48 89 d8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 48 89 df e8 9a 30 f4 ff <48> 8b 1b 48 89 de 48 83 e6 01 31 ff e8 59 70 8f ff 48 89 d8 48 83
RSP: 0018:ffffc90003f778a8 EFLAGS: 00010246
RAX: 1ffffd4c00072201 RBX: ffffea6000391008 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520007eef00 R12: 0000006000391000
R13: ffffea0000000000 R14: 200018000e4401fd R15: 00002000003ab000
FS:  00007ff35708f6c0(0000) GS:ffff8881258aa000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffea6000391008 CR3: 0000000074390000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	c1 ec 06             	shr    $0x6,%esp
   3:	4b 8d 1c 2c          	lea    (%r12,%r13,1),%rbx
   7:	48 83 c3 08          	add    $0x8,%rbx
   b:	48 89 d8             	mov    %rbx,%rax
   e:	48 c1 e8 03          	shr    $0x3,%rax
  12:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  19:	fc ff df
  1c:	80 3c 08 00          	cmpb   $0x0,(%rax,%rcx,1)
  20:	74 08                	je     0x2a
  22:	48 89 df             	mov    %rbx,%rdi
  25:	e8 9a 30 f4 ff       	call   0xfff430c4
* 2a:	48 8b 1b             	mov    (%rbx),%rbx <-- trapping instruction
  2d:	48 89 de             	mov    %rbx,%rsi
  30:	48 83 e6 01          	and    $0x1,%rsi
  34:	31 ff                	xor    %edi,%edi
  36:	e8 59 70 8f ff       	call   0xff8f7094
  3b:	48 89 d8             	mov    %rbx,%rax
  3e:	48                   	rex.W
  3f:	83                   	.byte 0x83


---
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@googlegroups.com.

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 syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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If you want to undo deduplication, reply with:
#syz undup


^ permalink raw reply	[flat|nested] 7+ messages in thread
* Re: [PATCH 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole
@ 2025-07-31  1:52 Hillf Danton
  2025-07-31  2:56 ` [syzbot] [mm?] BUG: unable to handle kernel paging request in move_pages syzbot
  0 siblings, 1 reply; 7+ messages in thread
From: Hillf Danton @ 2025-07-31  1:52 UTC (permalink / raw)
  To: Suren Baghdasaryan
  Cc: akpm, peterx, lokeshgidra, linux-mm, linux-kernel,
	syzkaller-bugs, syzbot, stable

#syz test

When UFFDIO_MOVE is used with UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES and it
encounters a non-present THP, it fails to properly recognize an unmapped
hole and tries to access a non-existent folio, resulting in
a crash. Add a check to skip non-present THPs.

Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: stable@vger.kernel.org
---
 mm/userfaultfd.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index cbed91b09640..60be8080ddd0 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1818,27 +1818,35 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
 
 		ptl = pmd_trans_huge_lock(src_pmd, src_vma);
 		if (ptl) {
-			/* Check if we can move the pmd without splitting it. */
-			if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
-			    !pmd_none(dst_pmdval)) {
-				struct folio *folio = pmd_folio(*src_pmd);
+			if (pmd_present(*src_pmd) || is_pmd_migration_entry(*src_pmd)) {
+				/* Check if we can move the pmd without splitting it. */
+				if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
+				    !pmd_none(dst_pmdval)) {
+					if (pmd_present(*src_pmd)) {
+						struct folio *folio = pmd_folio(*src_pmd);
+
+						if (!folio || (!is_huge_zero_folio(folio) &&
+							       !PageAnonExclusive(&folio->page))) {
+							spin_unlock(ptl);
+							err = -EBUSY;
+							break;
+						}
+					}
 
-				if (!folio || (!is_huge_zero_folio(folio) &&
-					       !PageAnonExclusive(&folio->page))) {
 					spin_unlock(ptl);
-					err = -EBUSY;
-					break;
+					split_huge_pmd(src_vma, src_pmd, src_addr);
+					/* The folio will be split by move_pages_pte() */
+					continue;
 				}
 
+				err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
+							  dst_pmdval, dst_vma, src_vma,
+							  dst_addr, src_addr);
+			} else {
+				/* nothing to do to move a hole */
 				spin_unlock(ptl);
-				split_huge_pmd(src_vma, src_pmd, src_addr);
-				/* The folio will be split by move_pages_pte() */
-				continue;
+				err = 0;
 			}
-
-			err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
-						  dst_pmdval, dst_vma, src_vma,
-						  dst_addr, src_addr);
 			step_size = HPAGE_PMD_SIZE;
 		} else {
 			if (pmd_none(*src_pmd)) {

base-commit: 01da54f10fddf3b01c5a3b80f6b16bbad390c302
-- 
2.50.1.552.g942d659e1b-goog


^ permalink raw reply	[flat|nested] 7+ messages in thread
end of thread, other threads:[~2025-07-31  2:56 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2025-07-17 19:13 [syzbot] [mm?] BUG: unable to handle kernel paging request in move_pages syzbot
2025-07-28 21:08 ` Peter Xu
2025-07-29  2:51   ` Suren Baghdasaryan
2025-07-29  8:08     ` Lokesh Gidra
2025-07-29 17:51       ` Suren Baghdasaryan
2025-07-30 17:09         ` Suren Baghdasaryan
2025-07-31  1:52 [PATCH 1/1] userfaultfd: fix a crash when UFFDIO_MOVE handles a THP hole Hillf Danton
2025-07-31  2:56 ` [syzbot] [mm?] BUG: unable to handle kernel paging request in move_pages syzbot

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