[BUG] null pointer dereference when loading bpf_preload on Raspberry Pi

Peter Robinson pbrobinson at gmail.com
Wed Jun 15 01:31:23 PDT 2022 

Hi Stefan,

> > Jan Palus already reported this NULL pointer dereference on bugzilla
> > [1], but i want to make sure this is noticed by the right people.
> >
> > I've i boot my Raspberry Pi 3 B Plus with multi_v7_defconfig and the
> > following config settings:
> >
> > CONFIG_BPF_SYSCALL=y
> > CONFIG_BPF_JIT=y
> > CONFIG_BPF_JIT_ALWAYS_ON=y
> > CONFIG_BPF_JIT_DEFAULT_ON=y
> > CONFIG_BPF_UNPRIV_DEFAULT_OFF=y
> > CONFIG_USERMODE_DRIVER=y
> > CONFIG_BPF_PRELOAD=y
> > CONFIG_BPF_PRELOAD_UMD=m
> are you able to see this issue in 5.18.x, too? I'm asking because the
> BPF settings comes from your configuration.

I've not seen it in a standard boot, is there a simple way to test
this, TBH I've never really played with bpf (it's on the todo list) so
if there's an easy test I can certainly check.

> >
> > The kernel (Linux 5.18.3) crashes with a null pointer deference:
> >
> > [    5.551587] Unable to handle kernel NULL pointer dereference at
> > virtual address 00000048
> > [    5.564467] [00000048] *pgd=39a12835
> > [    5.572700] Internal error: Oops: 17 [#1] SMP ARM
> > [    5.581249] Modules linked in: bpf_preload(+)
> > [    5.589400] CPU: 1 PID: 85 Comm: modprobe Not tainted 5.18.3 #1
> > [    5.597966] usb 1-1.1: new high-speed USB device number 3 using dwc2
> > [    5.599251] Hardware name: BCM2835
> > [    5.616839] PC is at mmiocpy+0xc8/0x334
> > [    5.624534] LR is at copy_from_bpfptr+0x60/0x80
> > [    5.632973] pc : [<c06e77e8>]    lr : [<c03fee50>]    psr: 60000013
> > [    5.643146] sp : f1515b30  ip : f1515b48  fp : f1515b30
> > [    5.652331] r10: c328e040  r9 : f1515b68  r8 : 00000000
> > [    5.661506] r7 : c328e040  r6 : 00000002  r5 : 00000048  r4 : 00000002
> > [    5.672037] r3 : 0000003d  r2 : 00000000  r1 : 00000048  r0 : f1515c08
> > [    5.682572] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM
> > Segment none
> > [    5.693670] Control: 10c5383d  Table: 023c406a  DAC: 00000051
> > [    5.703426] Register r0 information: 2-page vmalloc region starting
> > at 0xf1514000 allocated at kernel_clone+0x98/0x27c
> > [    5.718310] Register r1 information: non-paged memory
> > [    5.727454] Register r2 information: NULL pointer
> > [    5.736205] Register r3 information: non-paged memory
> > [    5.738825] hub 1-1.1:1.0: USB hub found
> > [    5.745334] Register r4 information: non-paged memory
> > [    5.753345] hub 1-1.1:1.0: 3 ports detected
> > [    5.762358] Register r5 information: non-paged memory
> > [    5.762364] Register r6 information: non-paged memory
> > [    5.762368] Register r7 information: slab task_struct start
> > c328e040 pointer offset 0
> > [    5.800440] Register r8 information: NULL pointer
> > [    5.809029] Register r9 information: 2-page vmalloc region starting
> > at 0xf1514000 allocated at kernel_clone+0x98/0x27c
> > [    5.823843] Register r10 information: slab task_struct start
> > c328e040 pointer offset 0
> > [    5.835847] Register r11 information: 2-page vmalloc region
> > starting at 0xf1514000 allocated at kernel_clone+0x98/0x27c
> > [    5.850796] Register r12 information: 2-page vmalloc region
> > starting at 0xf1514000 allocated at kernel_clone+0x98/0x27c
> > [    5.865664] Process modprobe (pid: 85, stack limit = 0x(ptrval))
> > [    5.867961] usb 1-1.3: new low-speed USB device number 4 using dwc2
> > [    5.875679] Stack: (0xf1515b30 to 0xf1516000)
> > [    5.894419] 5b20:                                     f1515c08
> > 00000002 00000000 c03fee50
> > [    5.906750] 5b40: 00000048 c051aa3d 00000000 c0402520 ef80327c
> > ef80328c c2001180 f1515c08
> > [    5.919097] 5b60: c1a45808 00012cc0 00000048 c051aa3d c3022440
> > 00000001 c2ee9898 ffffffff
> > [    5.931435] 5b80: 00000000 f1515bb4 00000000 00000000 c2ee9a48
> > 5beb87ed c22c4c8c 00000000
> > [    5.943733] 5ba0: 00000001 c328e040 00000000 00012cc0 00000dc0
> > 00000000 f1515f38 c048fb58
> > [    5.956089] 5bc0: f1515c00 00000000 c328e040 c217c000 4a389946
> > 00000001 00012cc0 ef7ff780
> > [    5.968456] 5be0: 00000000 4a389946 00000005 00000001 00000001
> > c328e2c0 c1804d8c c036a868
> > [    5.980852] 5c00: 00000801 ef7ff780 00000000 00000000 00000000
> > 00000000 00000000 00000000
> > [    5.993238] 5c20: 00000000 00000000 00000000 00000000 00000000
> > 00000000 00000000 00000000
> > [    6.005643] 5c40: 00000000 00000000 00000000 00000000 00000000
> > 00000000 00000000 00000000
> > [    6.018026] 5c60: 00000000 00000000 00000000 00000000 00000000
> > 00000000 00000000 00000000
> > [    6.030371] 5c80: 00000000 00000000 00000000 00000000 00000000
> > 00000000 00000019 5beb87ed
> > [    6.042719] 5ca0: c2004208 000017a8 00000048 c328e040 ffffffff
> > 00000000 c328e040 c328e040
> > [    6.055020] 5cc0: 00000000 c04043ec 00005dd9 7fffffff c2004208
> > 00000048 c051aa3d 5beb87ed
> > [    6.067330] 5ce0: 00005df9 000017a8 c328e040 c328e040 ffffffff
> > 00000000 c328e040 0000017b
> > [    6.079612] 5d00: 00000000 bf0031e0 00000002 00000004 000017a8
> > 00000001 00000000 00000000
> > [    6.091957] 5d20: 00000000 6f6c5f5f 72656461 70616d2e 00000000
> > 00000000 00000000 00000000
> > [    6.104254] 5d40: 00000000 00000000 00000000 00000000 c328e040
> > c0380594 c1325856 00000001
> > [    6.116521] 5d60: c23729a0 c051b97c c23729a0 5beb87ed 00000000
> > 00000000 c200423c c1a4a551
> > [    6.117969] usb 1-1.1.2: new low-speed USB device number 5 using dwc2
> > [    6.128707] 5d80: c2372a50 00000001 c1325856 00000124 c2372a50
> > c051b97c c2372a50 5beb87ed
> > [    6.128716] 5da0: 00000000 c22d1980 f1515e6c bf00322c ffffffff
> > 00000000 c2372a50 00000000
> > [    6.163743] 5dc0: 00000030 00000000 c2372a50 c0f179f0 c2348280
> > ef87f900 c2001180 c328e040
> > [    6.176062] 5de0: c04897dc 00000013 c0464698 c22d1980 c22d1980
> > 00000062 00000cc0 c049d584
> > [    6.188380] 5e00: 00000cc0 c328e040 c22d1980 5beb87ed 00000001
> > 00000cc0 00000062 bf00a05c
> > [    6.200720] 5e20: ffffffff c1a4a9e0 c328e040 0000017b 00000000
> > c0464698 c2348280 5beb87ed
> > [    6.213033] 5e40: 00000002 c328e040 bf007280 5beb87ed c22d1980
> > bf007280 c328e040 c2348280
> > [    6.225441] 5e60: 00000000 bf00a0e0 00000001 c2348280 bf0040b7
> > bf005860 000017a8 000008a8
> > [    6.237841] 5e80: 00000000 5beb87ed c328e040 bf00a000 c23481c0
> > 00000000 c1a4a9e0 c0301f30
> > [    6.250269] 5ea0: c357a3c0 c357a3c0 00000000 00000000 00000000
> > 00000000 c03c17f0 c23481c0
> > [    6.262591] 5ec0: c2001180 00000cc0 c03c17f0 c049d888 00000cc0
> > 00000000 c23481c0 5beb87ed
> > [    6.274942] 5ee0: 00000000 bf007040 0002d064 5beb87ed bf007040
> > 0002d064 c23481c0 c328e040
> > [    6.287336] 5f00: c0300324 c03c1810 bf007040 0000008f 00000000
> > 0002d064 00000000 c03c3ce4
> > [    6.299841] 5f20: f1515f34 7fffffff 00000000 00000002 c353e040
> > f151b000 f151d8cf f151d940
> > [    6.312151] 5f40: f151b000 00003f1c f151e904 f151e760 f151e25c
> > 00005000 00005150 00002884
> > [    6.324534] 5f60: 00005241 00000000 00000000 00000000 00002874
> > 00000024 00000025 0000001b
> > [    6.336923] 5f80: 00000000 00000017 00000000 5beb87ed 00000000
> > bbbecb00 000417d8 00000000
> > [    6.349310] 5fa0: 0000017b c03000c0 bbbecb00 000417d8 00000000
> > 0002d064 00000000 0002ec3c
> > [    6.361662] 5fc0: bbbecb00 000417d8 00000000 0000017b 00042ce0
> > 00000000 00042c38 00000000
> > [    6.374053] 5fe0: be8e3a88 be8e3a78 00022cb8 b6cb3ae0 60000010
> > 00000000 00000000 00000000
> > [    6.386437]  mmiocpy from copy_from_bpfptr+0x60/0x80
> > [    6.395558]  copy_from_bpfptr from __sys_bpf+0x78/0x1d30
> > [    6.404992]  __sys_bpf from bpf_sys_bpf+0x214/0x238
> > [    6.413982]  bpf_sys_bpf from skel_map_create.constprop.0+0x60/0x80
> > [bpf_preload]
> > [    6.425677]  skel_map_create.constprop.0 [bpf_preload] from
> > bpf_load_and_run.constprop.0+0x2c/0x1f8 [bpf_preload]
> > [    6.440256]  bpf_load_and_run.constprop.0 [bpf_preload] from
> > load+0xe0/0x1000 [bpf_preload]
> > [    6.452929]  load [bpf_preload] from do_one_initcall+0x68/0x170
> > [    6.463114]  do_one_initcall from do_init_module+0x3c/0x1e0
> > [    6.472955]  do_init_module from sys_finit_module+0xc8/0xd4
> > [    6.482802]  sys_finit_module from ret_fast_syscall+0x0/0x54
> > [    6.492679] Exception stack(0xf1515fa8 to 0xf1515ff0)
> > [    6.501975] 5fa0:                   bbbecb00 000417d8 00000000
> > 0002d064 00000000 0002ec3c
> > [    6.514476] 5fc0: bbbecb00 000417d8 00000000 0000017b 00042ce0
> > 00000000 00042c38 00000000
> > [    6.526999] 5fe0: be8e3a88 be8e3a78 00022cb8 b6cb3ae0
> > [    6.536392] Code: e480e004 e8bd0360 e1b02f82 14d13001 (24d14001)
> > [    6.546878] ---[ end trace 0000000000000000 ]---
> >
> > It would be nice to get a hint, how to narrow down or which commit
> > might trigger this issue.
> >
> > [1] - https://bugzilla.kernel.org/show_bug.cgi?id=216105
> >

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