Error while loading dw-i3c-master: UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:885:12

[Louis Sautier]

Hello,

I'm running into a bug when loading the dw-i3c-master module on kernel 
6.18 on one specific server. I suspect it has to do with the large 
number of CPUs on the machine (768 threads, from 2 AMD EPYC 9965 
processors) but I am not sure.

The system is on Ubuntu 25.10 and a 6.18 kernel with 
https://gist.githubusercontent.com/sbraz/a6f37fafbcf9354bbe4eace9e9eb48cb/raw/115da594dc9d7ea99b06754847571e6fd76d9da5/config 
(basically Ubuntu's).

These are the logs I see whenever I run "modprobe dw-i3c-master". Full 
dmesg at 
https://gist.githubusercontent.com/sbraz/a6f37fafbcf9354bbe4eace9e9eb48cb/raw/115da594dc9d7ea99b06754847571e6fd76d9da5/dmesg

dw-i3c-master AMDI0015:00: probe with driver dw-i3c-master failed with 
error -110
dw-i3c-master AMDI0015:01: probe with driver dw-i3c-master failed with 
error -110
------------[ cut here ]------------
UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:885:12
shift exponent 64 is too large for 64-bit type 'long unsigned int'
CPU: 109 UID: 0 PID: 7574 Comm: (udev-worker) Not tainted 6.18.0 #1 
PREEMPT(voluntary)
Hardware name: Giga Computing MZ73-LM2-000/MZ73-LM2-000, BIOS R23_F43 
11/28/2025
Call Trace:
  <TASK>
  dump_stack_lvl+0x5f/0x90
  dump_stack+0x10/0x18
  ubsan_epilogue+0x9/0x39
  __ubsan_handle_shift_out_of_bounds.cold+0xdd/0x1c9
  dw_i3c_master_daa.cold+0x1a/0x90 [dw_i3c_master]
  i3c_master_do_daa+0x30/0x90 [i3c]
  i3c_master_register+0x616/0xa80 [i3c]
  dw_i3c_common_probe+0x23f/0x2c0 [dw_i3c_master]
  dw_i3c_probe+0x30/0x50 [dw_i3c_master]
  platform_probe+0x42/0xc0
  ? driver_sysfs_add+0x63/0xd0
  really_probe+0xf9/0x370
  ? pm_runtime_barrier+0x56/0xa0
  __driver_probe_device+0x8b/0x160
  driver_probe_device+0x24/0xd0
  ? __pfx___driver_attach+0x10/0x10
  __driver_attach+0xef/0x220
  ? __pfx_dw_i3c_driver_init+0x10/0x10 [dw_i3c_master]
  bus_for_each_dev+0x8a/0xe0
  driver_attach+0x1e/0x30
  bus_add_driver+0x13e/0x230
  ? __pfx_dw_i3c_driver_init+0x10/0x10 [dw_i3c_master]
  driver_register+0x75/0xf0
  __platform_driver_register+0x1e/0x30
  dw_i3c_driver_init+0x1c/0xff0 [dw_i3c_master]
  do_one_initcall+0x59/0x330
  do_init_module+0x8b/0x290
  load_module+0x1f2f/0x2320
  init_module_from_file+0x9b/0x100
  ? init_module_from_file+0x9b/0x100
  idempotent_init_module+0x10e/0x300
  __x64_sys_finit_module+0x73/0xf0
  ? __secure_computing+0x84/0xe0
  x64_sys_call+0x1f04/0x2350
  do_syscall_64+0x82/0xc80
  ? exit_to_user_mode_loop+0xe6/0x190
  ? do_syscall_64+0x25c/0xc80
  ? restore_fpregs_from_fpstate+0x46/0xe0
  ? switch_fpu_return+0x5c/0xf0
  ? do_syscall_64+0x25c/0xc80
  ? switch_fpu_return+0x5c/0xf0
  ? do_syscall_64+0x25c/0xc80
  ? wait_for_completion_interruptible+0x24/0x50
  ? idempotent_init_module+0x1d5/0x300
  ? __rseq_handle_notify_resume+0xa2/0x4e0
  ? restore_fpregs_from_fpstate+0x46/0xe0
  ? switch_fpu_return+0x5c/0xf0
  ? do_syscall_64+0x25c/0xc80
  ? do_user_addr_fault+0x22b/0x6b0
  ? irqentry_exit_to_user_mode+0x2e/0x2a0
  ? irqentry_exit+0x43/0x50
  ? exc_page_fault+0x90/0x1b0
  entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7dff23f348cd
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 
f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 
f0 ff ff 73 01 c3 48 8b 0d 13 f5 0f 00 f7 d8 64 89 01 48
RSP: 002b:00007fff46db08c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 00005705ce7b5300 RCX: 00007dff23f348cd
RDX: 0000000000000000 RSI: 00007dff23c31336 RDI: 0000000000000078
RBP: 00007fff46db0960 R08: 0000000000000000 R09: 00005705ce77f530
R10: 0000000000000000 R11: 0000000000000246 R12: 00007dff23c31336
R13: 0000000000020000 R14: 00005705ce7bcb10 R15: 00005705ce7c4f00
  </TASK>
---[ end trace ]---
dw-i3c-master AMDI0015:03: probe with driver dw-i3c-master failed with 
error -110


I hope this is the right venue to report this. Please let me know if you 
need more information or if you would like me to test a patch.

Can you also keep me CC'd to replies? I'm not subscribed to the list.

Cheers,

Louis