I'm seeing this on every boot on 4.19 kernel with a whiskeylake platform:

2019-01-08T02:42:34.312313+00:00 WARNING kernel: [    3.682375] ------------[ cut here ]------------
2019-01-08T02:42:34.312314+00:00 WARNING kernel: [    3.682383] Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLUB object 'task_struct' (offset 1864, size 8)!
2019-01-08T02:42:34.312315+00:00 WARNING kernel: [    3.682394] WARNING: CPU: 3 PID: 1 at ../../../../../tmp/portage/sys-kernel/chromeos-kernel-4_19-4.19.13-r110/work/chromeos-kernel-4_19-4.19.13/mm/usercopy.c:83 usercopy_warn+0x95/0x9a
2019-01-08T02:42:34.312316+00:00 WARNING kernel: [    3.682396] Modules linked in:
2019-01-08T02:42:34.312317+00:00 WARNING kernel: [    3.682400] CPU: 3 PID: 1 Comm: init Not tainted 4.19.13-02687-g2134dc1dc8fd #1
2019-01-08T02:42:34.312319+00:00 WARNING kernel: [    3.682402] Hardware name: Google Arcada/Arcada, BIOS Google_Arcada.11444.0.2018_12_21_1744 12/22/2018
2019-01-08T02:42:34.312320+00:00 WARNING kernel: [    3.682405] RIP: 0010:usercopy_warn+0x95/0x9a
2019-01-08T02:42:34.312321+00:00 WARNING kernel: [    3.682408] Code: c6 04 25 b2 6d f2 a5 01 48 c7 c3 b4 7f c2 a5 48 0f 44 d8 48 c7 c7 36 7f c2 a5 31 c0 41 52 41 53 53 e8 f2 e7 ea ff 48 83 c4 18 <0f> 0b 5b 5d c3 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 41 54 53 48
2019-01-08T02:42:34.312322+00:00 WARNING kernel: [    3.682410] RSP: 0018:ffffbbd7c0013ce8 EFLAGS: 00010286
2019-01-08T02:42:34.312323+00:00 WARNING kernel: [    3.682413] RAX: 81cb547d15790900 RBX: ffffffffa5c27fb4 RCX: ffffffffa5e52320
2019-01-08T02:42:34.312324+00:00 WARNING kernel: [    3.682415] RDX: 0000000000000001 RSI: 0000000000000082 RDI: ffffffffa5e522f0
2019-01-08T02:42:34.312326+00:00 WARNING kernel: [    3.682417] RBP: ffffbbd7c0013cf0 R08: 0000000000000000 R09: 0000000000000007
2019-01-08T02:42:34.312327+00:00 WARNING kernel: [    3.682418] R10: fffffffffffffd6f R11: ffffffffa4f20264 R12: ffffa357a5190750
2019-01-08T02:42:34.312328+00:00 WARNING kernel: [    3.682420] R13: ffffa357a5190000 R14: 0000000000000008 R15: 0000000000000001
2019-01-08T02:42:34.312329+00:00 WARNING kernel: [    3.682423] FS:  00007d404eb75500(0000) GS:ffffa357a6380000(0000) knlGS:0000000000000000
2019-01-08T02:42:34.312330+00:00 WARNING kernel: [    3.682425] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
2019-01-08T02:42:34.312330+00:00 WARNING kernel: [    3.682427] CR2: 000056c2374722f0 CR3: 0000000262f16002 CR4: 00000000003606e0
2019-01-08T02:42:34.312331+00:00 WARNING kernel: [    3.682428] Call Trace:
2019-01-08T02:42:34.312334+00:00 WARNING kernel: [    3.682435]  __check_object_size+0xd2/0x1bb
2019-01-08T02:42:34.312335+00:00 WARNING kernel: [    3.682439]  do_signal+0x460/0x56b
2019-01-08T02:42:34.312335+00:00 WARNING kernel: [    3.682444]  prepare_exit_to_usermode+0x86/0x109
2019-01-08T02:42:34.312336+00:00 WARNING kernel: [    3.682447]  syscall_return_slowpath+0x42/0x175
2019-01-08T02:42:34.312337+00:00 WARNING kernel: [    3.682451]  ? __se_sys_select+0x88/0xe6
2019-01-08T02:42:34.312338+00:00 WARNING kernel: [    3.682454]  ? ksys_read+0x71/0x9b
2019-01-08T02:42:34.312341+00:00 WARNING kernel: [    3.682458]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
2019-01-08T02:42:34.312341+00:00 WARNING kernel: [    3.682461] RIP: 0033:0x7d404e5c0f07
2019-01-08T02:42:34.312342+00:00 WARNING kernel: [    3.682464] Code: 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 8d 05 81 2d 2c 00 49 89 ca 8b 00 85 c0 75 28 b8 17 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 8b 15 31 cf 2b 00 f7 d8 64 89 02 b8
2019-01-08T02:42:34.312343+00:00 WARNING kernel: [    3.682466] RSP: 002b:00007ffde1de3178 EFLAGS: 00000246 ORIG_RAX: 0000000000000017
2019-01-08T02:42:34.312344+00:00 WARNING kernel: [    3.682468] RAX: fffffffffffffffc RBX: 00007ffde1de31d0 RCX: 00007d404e5c0f07
2019-01-08T02:42:34.312345+00:00 WARNING kernel: [    3.682470] RDX: 00007ffde1de3250 RSI: 00007ffde1de32d0 RDI: 0000000000000008
2019-01-08T02:42:34.312348+00:00 WARNING kernel: [    3.682472] RBP: 00007ffde1de3380 R08: 0000000000000000 R09: 00000000000019e0
2019-01-08T02:42:34.312348+00:00 WARNING kernel: [    3.682474] R10: 00007ffde1de31d0 R11: 0000000000000246 R12: 00007ffde1de31d0
2019-01-08T02:42:34.312349+00:00 WARNING kernel: [    3.682476] R13: 00007ffde1de3250 R14: 00007ffde1de31cf R15: 00007ffde1de3190
2019-01-08T02:42:34.312350+00:00 WARNING kernel: [    3.682478] ---[ end trace fed4d28691641466 ]---