Null pointer deference due to KCOV

[shenki]

4.18.8-00344-gbb5e0c8 with KCOV and GCC_PLUGIN_STRUCTLEAK turned on.

[   28.871525] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[   28.879929] pgd = b9f4bf0b
[   28.882744] [00000000] *pgd=00000000
[   28.886463] Internal error: Oops: 5 [#1] ARM
[   28.890891] CPU: 0 PID: 1 Comm: init Tainted: G                T 4.18.8-00344-gbb5e0c8 #20
[   28.899237] Hardware name: Generic DT based system
[   28.904189] PC is at v4wb_copy_user_page+0x14/0x50
[   28.909123] LR is at v4wb_copy_user_page+0xc/0x50
[   28.913935] pc : [<80114720>]    lr : [<80114718>]    psr: 80000013
[   28.920295] sp : 9d477af0  ip : 9d477af8  fp : 9d477b2c
[   28.925615] r10: 9db9b200  r9 : 9d7df1c0  r8 : 0037b200
[   28.930950] r7 : 9d403f80  r6 : 46af1000  r5 : 9bd90000  r4 : 80bfe000
[   28.937577] r3 : 9d474da0  r2 : 00000040  r1 : 00000000  r0 : 80bfe000
[   28.944205] Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[   28.951453] Control: 0005317f  Table: 5d7fc000  DAC: 00000051
[   28.957303] Process init (pid: 1, stack limit = 0x6344fd84)
[   28.962979] Stack: (0x9d477af0 to 0x9d478000)
[   28.967495] 7ae0:                                     80bfe000 80114718 46af1830 9d403f80
[   28.975876] 7b00: 9d477b2c 80c03008 8090b880 00000200 9d403f80 9d7fd1a8 46af1830 9d403f80
[   28.984256] 7b20: 9d477bb4 9d477b30 80287950 8011476c 9d477b94 9d477b40 802d4c70 801a8980
[   28.992630] 7b40: 21f98280 00000000 00000001 9d403f80 00000015 006200c2 00000021 46af1000
[   29.001000] 7b60: 9d7fd1a8 9d7fd1a8 00000000 9d837fc0 00000000 9db9b200 00000000 00000000
[   29.009375] 7b80: 00000000 cb5707e3 9d477bb4 9d477d10 9d474da0 00000000 9d7df1c0 00000805
[   29.017750] 7ba0: 46af1830 9d403f80 9d477c0c 9d477bb8 8010d478 80287198 00000000 00000000
[   29.026122] 7bc0: 00000000 00000000 00000000 00000002 00000800 9d7df2e8 00000002 00000015
[   29.034504] 7be0: 9d477c4c 46af1830 9d477d10 80c03008 00000805 46af1830 9d477d10 7f3f5494
[   29.042885] 7c00: 9d477c44 9d477c10 8010d710 8010d0f0 00100877 80a37b34 9d477c4c 00000005
[   29.051267] 7c20: 00000805 80c03008 80c0abc0 46af1830 9d477d10 7f3f5494 9d477d0c 9d477c48
[   29.059643] 7c40: 8010d7a4 8010d638 8028fcb8 801a8980 9d403d84 00000000 9d521700 00000000
[   29.068012] 7c60: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   29.076376] 7c80: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   29.084741] 7ca0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   29.093105] 7cc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 cb5707e3
[   29.101488] 7ce0: fffff000 8043dbb0 00000013 ffffffff 9d477d44 7f000000 9d476000 00000000
[   29.109867] 7d00: 9d477d9c 9d477d10 80101958 8010d738 00000000 00000001 00000055 00000055
[   29.118249] 7d20: 9d476000 46af1830 000007d0 80c03008 7f000000 00000000 00000000 9d477d9c
[   29.126632] 7d40: 9d477d60 9d477d60 8043db9c 8043dbb0 00000013 ffffffff 00000055 7f000000
[   29.135006] 7d60: 9d521700 00000003 9d477da4 cb5707e3 80271314 000007d0 46af1830 00000051
[   29.143384] 7d80: 00000000 9d477de0 80c03008 9d452400 9d477dbc 9d477da0 8043dd4c 8043daec
[   29.151762] 7da0: 000007d0 46af1830 00000051 00000000 9d477ddc 9d477dc0 80323690 8043dd24
[   29.160144] 7dc0: 9bad1a80 46af1908 9d778e40 00000000 9d477e84 9d477de0 80323000 80323620
[   29.168520] 7de0: 00100802 00000000 00000000 000af6b0 000adf08 0009deec 00010000 9d452400
[   29.176889] 7e00: 9d477de0 00000000 00000003 00000006 46af1908 00000001 00000000 00010000
[   29.185267] 7e20: 46af1830 9d778d80 00000000 9d521700 9d775c00 9d77ea00 00000034 00000000
[   29.193650] 7e40: 9d477e84 9d477e50 8031fdcc 801a8980 80c03008 cb5707e3 9d452440 9d452400
[   29.202032] 7e60: 80c5094c 80c48f2c fffffff8 9d452440 00000000 9d452400 9d477ea4 9d477e88
[   29.210412] 7e80: 802b9128 80321cec 9d521a20 00000000 9d452400 80c03008 9d477edc 9d477ea8
[   29.218791] 7ea0: 8031fee0 802b90dc 9d477ed4 00000000 9d452442 cb5707e3 9bc00040 9d452400
[   29.227175] 7ec0: 80c508e4 80c48f2c 80c07ee0 80c07fc8 9d477efc 9d477ee0 802b9128 8031fbfc
[   29.235556] 7ee0: 9d5b0000 80c03008 9d474da0 80c07ee0 9d477f4c 9d477f00 802b97c8 802b90dc
[   29.243928] 7f00: 9d477f74 00000001 9d7df2e8 80c07fc8 00000001 00000001 00000000 cb5707e3
[   29.252300] 7f20: 00000000 9d5b0000 80c07ee0 80c07fc8 00000000 00000000 00000000 00000000
[   29.260674] 7f40: 9d477f74 9d477f50 802b9b74 802b91d8 00000000 00000000 00000000 80c07ecc
[   29.269058] 7f60: 809c6848 00000000 9d477f8c 9d477f78 80102748 802b9b3c 809c6848 80cf6c60
[   29.277438] 7f80: 9d477fac 9d477f90 808a9ac8 80102720 00000000 808a9a44 00000000 808a9a44
[   29.285811] 7fa0: 00000000 9d477fb0 801010e8 808a9a54 00000000 00000000 00000000 00000000
[   29.294178] 7fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   29.302543] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[   29.310966] [<80114720>] (v4wb_copy_user_page) from [<80114718>] (v4wb_copy_user_page+0xc/0x50)
[   29.319856] Code: e1a05001 eb025095 e92d4010 e3a02040 (e8b15018) 
[   29.326329] ---[ end trace 36711fbbd96cdb73 ]---

arch/arm/mm/copypage-v4wb.c has a call to __sanitizer_cov_trace_pc inserted into it. That looked like it was clearing r1, and then copypage was trying to save a bunch of registers into the address of r1.