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Date:   Sun, 21 Aug 2022 16:01:42 -0700
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Subject: Re: [syzbot] general protection fault in sanity_check_pinned_pages
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To:     Andrew Morton <akpm@linux-foundation.org>,
        syzbot <syzbot+c14f12d4b695168145b0@syzkaller.appspotmail.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com,
        Alistair Popple <apopple@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>
References: <000000000000fb7fc005e6baf0f3@google.com>
 <20220821013453.fea6ca8a3a4f241e6560ad79@linux-foundation.org>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <20220821013453.fea6ca8a3a4f241e6560ad79@linux-foundation.org>
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On 8/21/22 01:34, Andrew Morton wrote:

>> general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
>> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
>> CPU: 0 PID: 3608 Comm: syz-executor314 Not tainted 6.0.0-rc1-next-20220817-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
>> RIP: 0010:_compound_head include/linux/page-flags.h:253 [inline]
>> RIP: 0010:sanity_check_pinned_pages+0x25e/0xec0 mm/gup.c:52
> 
> Thanks.  Another GUP explosion.

OK, so what's happening here is that rds_cmsg_rdma_args() called
pin_user_pages_fast(), and after either finishing the RDS send
operation, *or* perhaps after failing early due to an error, it then
calls unpin_user_pages_dirty_lock(), which crashes due to a NULL page*
in the pages** array.

commit 4d1225cd5560 ("mm/gup.c: simplify and fix
check_and_migrate_movable_pages() return codes") gets involved in the
code that NULLs out pages during migration in gup.c, so it is under some
suspicion here.

A bisection would be very nice to have, but meanwhile I'll look at the
other gup crash that arrived in my inbox at the same time as this one.

thanks,
-- 
John Hubbard
NVIDIA

> 
>> Code: a2 06 00 00 e8 f3 8a c9 ff 4c 89 f0 48 c1 e8 03 80 3c 18 00 0f 85 8e 0a 00 00 4d 8b 26 49 8d 44 24 08 48 89 04 24 48 c1 e8 03 <80> 3c 18 00 0f 85 8b 0a 00 00 49 8b 6c 24 08 31 ff 49 89 ef 41 83
>> RSP: 0018:ffffc900039df6d0 EFLAGS: 00010202
>> RAX: 0000000000000001 RBX: dffffc0000000000 RCX: 0000000000000000
>> RDX: ffff88802763bb00 RSI: ffffffff81b28a5d RDI: 0000000000000007
>> RBP: 000000000000034e R08: 0000000000000007 R09: 0000000000000000
>> R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
>> R13: 0000000000000001 R14: ffffc900039df7c8 R15: 0000000000000000
>> FS:  00007fc2d0fe9700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 0000000020001600 CR3: 0000000076052000 CR4: 00000000003506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <TASK>
>>   unpin_user_pages_dirty_lock mm/gup.c:311 [inline]
>>   unpin_user_pages_dirty_lock+0x4a/0x4c0 mm/gup.c:299
>>   rds_rdma_free_op+0x28d/0x3c0 net/rds/rdma.c:501
>>   rds_cmsg_rdma_args+0x32c/0x1540 net/rds/rdma.c:797
>>   rds_cmsg_send net/rds/send.c:1005 [inline]
>>   rds_sendmsg+0x1c5c/0x3040 net/rds/send.c:1316
>>   sock_sendmsg_nosec net/socket.c:714 [inline]
>>   sock_sendmsg+0xcf/0x120 net/socket.c:734
>>   ____sys_sendmsg+0x6eb/0x810 net/socket.c:2482
>>   ___sys_sendmsg+0x110/0x1b0 net/socket.c:2536
>>   __sys_sendmsg+0xf3/0x1c0 net/socket.c:2565
>>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>   do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> RIP: 0033:0x7fc2d1036e39
>> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 14 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 b8 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007fc2d0fe9308 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>> RAX: ffffffffffffffda RBX: 00007fc2d10bf408 RCX: 00007fc2d1036e39
>> RDX: 0000000000000000 RSI: 0000000020001600 RDI: 0000000000000004
>> RBP: 00007fc2d10bf400 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc2d10bf40c
>> R13: 00007fc2d108d004 R14: 632e79726f6d656d R15: 0000000000022000
>>   </TASK>
>> Modules linked in:
>> ---[ end trace 0000000000000000 ]---
>> RIP: 0010:_compound_head include/linux/page-flags.h:253 [inline]
>> RIP: 0010:sanity_check_pinned_pages+0x25e/0xec0 mm/gup.c:52
>> Code: a2 06 00 00 e8 f3 8a c9 ff 4c 89 f0 48 c1 e8 03 80 3c 18 00 0f 85 8e 0a 00 00 4d 8b 26 49 8d 44 24 08 48 89 04 24 48 c1 e8 03 <80> 3c 18 00 0f 85 8b 0a 00 00 49 8b 6c 24 08 31 ff 49 89 ef 41 83
>> RSP: 0018:ffffc900039df6d0 EFLAGS: 00010202
>> RAX: 0000000000000001 RBX: dffffc0000000000 RCX: 0000000000000000
>> RDX: ffff88802763bb00 RSI: ffffffff81b28a5d RDI: 0000000000000007
>> RBP: 000000000000034e R08: 0000000000000007 R09: 0000000000000000
>> R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000000
>> R13: 0000000000000001 R14: ffffc900039df7c8 R15: 0000000000000000
>> FS:  00007fc2d0fe9700(0000) GS:ffff8880b9b00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 000000002034d000 CR3: 0000000076052000 CR4: 00000000003506e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> ----------------
>> Code disassembly (best guess):
>>     0:	a2 06 00 00 e8 f3 8a 	movabs %al,0xffc98af3e8000006
>>     7:	c9 ff
>>     9:	4c 89 f0             	mov    %r14,%rax
>>     c:	48 c1 e8 03          	shr    $0x3,%rax
>>    10:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
>>    14:	0f 85 8e 0a 00 00    	jne    0xaa8
>>    1a:	4d 8b 26             	mov    (%r14),%r12
>>    1d:	49 8d 44 24 08       	lea    0x8(%r12),%rax
>>    22:	48 89 04 24          	mov    %rax,(%rsp)
>>    26:	48 c1 e8 03          	shr    $0x3,%rax
>> * 2a:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1) <-- trapping instruction
>>    2e:	0f 85 8b 0a 00 00    	jne    0xabf
>>    34:	49 8b 6c 24 08       	mov    0x8(%r12),%rbp
>>    39:	31 ff                	xor    %edi,%edi
>>    3b:	49 89 ef             	mov    %rbp,%r15
>>    3e:	41                   	rex.B
>>    3f:	83                   	.byte 0x83
>>
>>
>> ---
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