Re: [syzbot] [net?] BUG: unable to handle kernel paging request in nsim_bpf

[syzbot <syzbot+44c2416196b7c607f226@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel paging request in nsim_xdp_set_prog

Unable to handle kernel paging request at virtual address dfff800000000004
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
Mem abort info:
  ESR = 0x0000000096000005
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x05: level 1 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000004] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 6540 Comm: syz-executor.0 Not tainted 6.6.0-rc7-syzkaller-00089-g8de1e7afcc1c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : nsim_prog_set_loaded drivers/net/netdevsim/bpf.c:100 [inline]
pc : nsim_bpf_offload drivers/net/netdevsim/bpf.c:113 [inline]
pc : nsim_xdp_offload_prog drivers/net/netdevsim/bpf.c:189 [inline]
pc : nsim_xdp_set_prog+0x3f4/0x568 drivers/net/netdevsim/bpf.c:208
lr : nsim_prog_set_loaded drivers/net/netdevsim/bpf.c:99 [inline]
lr : nsim_bpf_offload drivers/net/netdevsim/bpf.c:113 [inline]
lr : nsim_xdp_offload_prog drivers/net/netdevsim/bpf.c:189 [inline]
lr : nsim_xdp_set_prog+0x3d0/0x568 drivers/net/netdevsim/bpf.c:208
sp : ffff800097047730
x29: ffff800097047730 x28: dfff800000000000 x27: 1fffe000196b819f
x26: ffff800094eee000 x25: 1ffff000129ddc07 x24: dfff800000000000
x23: 0000000000000001 x22: ffff800094eee038 x21: 0000000000000020
x20: ffff0000cb5c0d18 x19: ffff800097047820 x18: ffff800097047580
x17: ffff8000805c1258 x16: ffff80008030c738 x15: 0000000000000000
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000001
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000000000000004 x7 : 0000000000000000 x6 : 0000000000000000
x5 : ffff800094eee000 x4 : 0000000000000000 x3 : ffff80008030c754
x2 : ffff0000cb5c0d18 x1 : 0000000000000001 x0 : 0000000000000000
Call trace:
 nsim_prog_set_loaded drivers/net/netdevsim/bpf.c:100 [inline]
 nsim_bpf_offload drivers/net/netdevsim/bpf.c:113 [inline]
 nsim_xdp_offload_prog drivers/net/netdevsim/bpf.c:189 [inline]
 nsim_xdp_set_prog+0x3f4/0x568 drivers/net/netdevsim/bpf.c:208
 nsim_bpf+0x5ac/0xaec
 dev_xdp_install+0x124/0x2f0 net/core/dev.c:9199
 dev_xdp_attach+0xa4c/0xcc8 net/core/dev.c:9351
 dev_xdp_attach_link net/core/dev.c:9370 [inline]
 bpf_xdp_link_attach+0x300/0x710 net/core/dev.c:9540
 link_create+0x2c0/0x68c kernel/bpf/syscall.c:4954
 __sys_bpf+0x4d4/0x5dc kernel/bpf/syscall.c:5414
 __do_sys_bpf kernel/bpf/syscall.c:5448 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5446 [inline]
 __arm64_sys_bpf+0x80/0x98 kernel/bpf/syscall.c:5446
 __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155
 el0_svc+0x54/0x158 arch/arm64/kernel/entry-common.c:678
 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:696
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595
Code: 96b36ecd f94002a8 91008115 d343fea8 (38f86908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	96b36ecd 	bl	0xfffffffffacdbb34
   4:	f94002a8 	ldr	x8, [x21]
   8:	91008115 	add	x21, x8, #0x20
   c:	d343fea8 	lsr	x8, x21, #3
* 10:	38f86908 	ldrsb	w8, [x8, x24] <-- trapping instruction


Tested on:

commit:         8de1e7af Merge branch 'for-next/core' into for-kernelci
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1097a35b680000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3e6feaeda5dcbc27
dashboard link: https://syzkaller.appspot.com/bug?extid=44c2416196b7c607f226
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=120c37df680000