Re: BUG: unable to handle kernel paging request in drm_fb_helper_dirty_work

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    435faf5c Merge tag 'riscv-for-linus-5.8-mw0' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14fed799100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3dbb617b9c2a5bdf
dashboard link: https://syzkaller.appspot.com/bug?extid=8a2039467425e497e64a
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15c1e011100000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12fed799100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8a2039467425e497e64a@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: unable to handle page fault for address: fffff520016dec00
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 7ffcd067 P4D 7ffcd067 PUD 2c920067 PMD 28203067 PTE 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 1221 Comm: kworker/1:2 Not tainted 5.7.0-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Workqueue: events drm_fb_helper_dirty_work
RIP: 0010:memory_is_nonzero mm/kasan/generic.c:120 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:134 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:165 [inline]
RIP: 0010:check_memory_region_inline mm/kasan/generic.c:183 [inline]
RIP: 0010:check_memory_region+0x9d/0x190 mm/kasan/generic.c:192
Code: c9 4d 0f 49 c1 49 c1 f8 03 45 85 c0 0f 84 03 01 00 00 41 83 e8 01 4e 8d 44 c0 08 eb 0d 48 83 c0 08 4c 39 c0 0f 84 b2 00 00 00 <48> 83 38 00 74 ed 4c 8d 40 08 eb 09 48 83 c0 01 49 39 c0 74 69 80
RSP: 0018:ffffc90003f47c20 EFLAGS: 00010216
RAX: fffff520016dec00 RBX: fffff520016dec00 RCX: ffffffff840645bd
RDX: 0000000000000001 RSI: 0000000000001000 RDI: ffffc9000b6f6000
RBP: fffff520016dee00 R08: fffff520016dee00 R09: 0000000000000200
R10: ffffc9000b6f6fff R11: fffff520016dedff R12: 0000000000001000
R13: ffffc9000b6f6000 R14: ffffc90009b47000 R15: ffff888078c65a00
FS:  0000000000000000(0000) GS:ffff88802cf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffff520016dec00 CR3: 00000000214d1000 CR4: 0000000000340ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 memcpy+0x39/0x60 mm/kasan/common.c:106
 memcpy include/linux/string.h:406 [inline]
 drm_fb_helper_dirty_blit_real drivers/gpu/drm/drm_fb_helper.c:386 [inline]
 drm_fb_helper_dirty_work+0x42d/0x760 drivers/gpu/drm/drm_fb_helper.c:415
 process_one_work+0x965/0x16a0 kernel/workqueue.c:2268
 worker_thread+0x96/0xe20 kernel/workqueue.c:2414
 kthread+0x388/0x470 kernel/kthread.c:268
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351
Modules linked in:
CR2: fffff520016dec00
---[ end trace fdb627f1507ae2fd ]---
RIP: 0010:memory_is_nonzero mm/kasan/generic.c:120 [inline]
RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:134 [inline]
RIP: 0010:memory_is_poisoned mm/kasan/generic.c:165 [inline]
RIP: 0010:check_memory_region_inline mm/kasan/generic.c:183 [inline]
RIP: 0010:check_memory_region+0x9d/0x190 mm/kasan/generic.c:192
Code: c9 4d 0f 49 c1 49 c1 f8 03 45 85 c0 0f 84 03 01 00 00 41 83 e8 01 4e 8d 44 c0 08 eb 0d 48 83 c0 08 4c 39 c0 0f 84 b2 00 00 00 <48> 83 38 00 74 ed 4c 8d 40 08 eb 09 48 83 c0 01 49 39 c0 74 69 80
RSP: 0018:ffffc90003f47c20 EFLAGS: 00010216
RAX: fffff520016dec00 RBX: fffff520016dec00 RCX: ffffffff840645bd
RDX: 0000000000000001 RSI: 0000000000001000 RDI: ffffc9000b6f6000
RBP: fffff520016dee00 R08: fffff520016dee00 R09: 0000000000000200
R10: ffffc9000b6f6fff R11: fffff520016dedff R12: 0000000000001000
R13: ffffc9000b6f6000 R14: ffffc90009b47000 R15: ffff888078c65a00
FS:  0000000000000000(0000) GS:ffff88802cf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffff520016dec00 CR3: 00000000214d1000 CR4: 0000000000340ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400