Error while loading dw-i3c-master: UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:885:12
Louis Sautier
louis.sautier at ovhcloud.com
Fri Dec 12 11:44:41 PST 2025
On 12/11/25 17:52, Frank Li wrote:
> On Wed, Dec 10, 2025 at 08:50:24PM +0100, Louis Sautier wrote:
>> On 12/10/25 16:20, Frank Li wrote:
>>> On Tue, Dec 09, 2025 at 08:52:46PM +0100, Louis Sautier wrote:
>>>> On 12/9/25 18:24, Frank Li wrote:
>>>>> On Tue, Dec 09, 2025 at 04:36:30PM +0100, Louis Sautier wrote:
>>>>>> On 12/9/25 13:48, Alexandre Belloni wrote:
>>>>>>> On 09/12/2025 12:37:12+0100, Louis Sautier wrote:
>>>>>>>> On 12/8/25 21:58, Alexandre Belloni wrote:
>>>>>>>>> Hello Louis,
>>>>>>>>>
>>>>>>>>> On 02/12/2025 21:17:31+0100, Louis Sautier wrote:
>>>>>>>>>> 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).
>>>>>>>>> Just to be sure, does this also happen with v6.17?
>>>>>>>>>
>>>>>>>>> The only change is the shutdown handling so I would guess yes.
>>>>>>>>>
>>>>>>>> Hello,
>>>>>>>>
>>>>>>>> It does happen with 6.17. I initially discovered this while running Ubuntu
>>>>>>>> 25.10's stock kernel (6.17.0).
>>>>>>>>
>>>>>>>>> What is the behavior when you build the dw-i3c-master as a static driver?
>>>>>>>> I'll try CONFIG_DW_I3C_MASTER=y and report back.
>>>>>>>>
>>>>>>>> Someone also suggested (they didn't reply to the list though) that I add a
>>>>>>>> printk to see what the value of maxdevs is. I'll provide the log as soon as
>>>>>>>> I have rebuilt with:
>>>>>>>>
>>>>>>>> --- linux-6.18.orig/drivers/i3c/master/dw-i3c-master.c 2025-11-30 22:42:10.000000000 +0000
>>>>>>>> +++ linux-6.18/drivers/i3c/master/dw-i3c-master.c 2025-12-08 18:17:33.151567225 +0000
>>>>>>>> @@ -1588,6 +1588,7 @@
>>>>>>>> ret = readl(master->regs + DEVICE_ADDR_TABLE_POINTER);
>>>>>>>> master->datstartaddr = ret;
>>>>>>>> master->maxdevs = ret >> 16;
>>>>>>>> + printk("maxdevs: %d\n", master->maxdevs);
>>>>>>>> master->free_pos = GENMASK(master->maxdevs - 1, 0);
>>>>>>>> master->quirks = (unsigned long)device_get_match_data(&pdev->dev);
>>>>>>>>
>>>>>>> Yes, that was going to be my suggestion.
>>>>>>>
>>>>>> I haven't tried with the driver built-in yet. This is what the printk shows:
>>>>>> dw-i3c-master AMDI0015:00: probe with driver dw-i3c-master failed with error
>>>>>> -110
>>>>>> maxdevs: 65535
>>>>> Maybe ret is bigger 0x8000_0000, and ret is sign int. so >>16 because -1.
>>>>>
>>>>> unsigned int val = readl(master->regs + DEVICE_ADDR_TABLE_POINTER);
>>>>>
>>>>> master->maxdevs = val >> 16;
>>>>>
>>>>> Frank
>>>> I tried this and CONFIG_DW_I3C_MASTER=y:
>>>>
>>>> --- linux-6.18.orig/drivers/i3c/master/dw-i3c-master.c 2025-11-30
>>>> 22:42:10.000000000 +0000
>>>> +++ linux-6.18/drivers/i3c/master/dw-i3c-master.c 2025-12-09
>>>> 19:21:52.735366616 +0000
>>>> @@ -1585,9 +1585,10 @@
>>>> ret = readl(master->regs + DATA_BUFFER_STATUS_LEVEL);
>>>> master->caps.datafifodepth = DATA_BUFFER_STATUS_LEVEL_TX(ret);
>>>>
>>>> - ret = readl(master->regs + DEVICE_ADDR_TABLE_POINTER);
>>>> - master->datstartaddr = ret;
>>>> - master->maxdevs = ret >> 16;
>>>> + unsigned int val = readl(master->regs + DEVICE_ADDR_TABLE_POINTER);
>>>> + master->datstartaddr = val;
>>>> + master->maxdevs = val >> 16;
>>>> + printk("maxdevs (unsigned): %d\n", master->maxdevs);
>>>> master->free_pos = GENMASK(master->maxdevs - 1, 0);
>>>>
>>>> master->quirks = (unsigned long)device_get_match_data(&pdev->dev);
>>>>
>>>> And I get this log, so no change, really. I assume there's only one
>>>> "maxdevs" log because there is only one attempt to load the built-in driver?
>>> It may have dependence missed at drivers. such as clock. when built-in,
>>> this driver probe first before clock ready.
>>>
>>> If build as module, other driver help enable this clock. So it can get
>>> correct value.
>>>
>>> Frank
>> My bad, I checked yesterday's entire log again and actually, there are still
>> 4 maxdevs printk logs:
>>
>> Built-in driver:
>>
>> # journalctl -b -2 --grep "maxdevs|UBSAN" -o short-monotonic
>> [ 23.162996] ns31482903 kernel: maxdevs (unsigned): 65535
> Look this instance miss config some resource, like clks. So clock have
> not enable, all register return 0xFFFFFFFF.
>
> Frank
Can you help me understand why this happens and how to fix this? Could
this be a hardware problem?
Should I open a downstream Ubuntu bug report, would that be helpful?
>
>> [ 23.163008] ns31482903 kernel: UBSAN: shift-out-of-bounds in
>> drivers/i3c/master/dw-i3c-master.c:1592:21
>> [ 23.166508] ns31482903 kernel: maxdevs (unsigned): 65535
>> [ 23.166568] ns31482903 kernel: maxdevs (unsigned): 11
>> [ 23.166576] ns31482903 kernel: UBSAN: shift-out-of-bounds in
>> drivers/i3c/master/dw-i3c-master.c:885:12
>> [ 23.166748] ns31482903 kernel: maxdevs (unsigned): 11
>>
>>
>> I rebuilt with CONFIG_DW_I3C_MASTER=m and I get the same logs although the
>> timing differs a little:
>>
>> # journalctl -b -1 --grep "maxdevs|UBSAN" -o short-monotonic
>> [ 14.507929] ns31482903 kernel: maxdevs (unsigned): 65535
>> [ 14.507957] ns31482903 kernel: UBSAN: shift-out-of-bounds in
>> drivers/i3c/master/dw-i3c-master.c:1592:21
>> [ 16.683035] ns31482903 kernel: maxdevs (unsigned): 65535
>> [ 18.872323] ns31482903 kernel: maxdevs (unsigned): 11
>> [ 18.872362] ns31482903 kernel: UBSAN: shift-out-of-bounds in
>> drivers/i3c/master/dw-i3c-master.c:885:12
>> [ 18.882020] ns31482903 kernel: maxdevs (unsigned): 11
>>
>> Did I miss something with the unsigned patch?
>>>> maxdevs (unsigned): 65535
>>>> ------------[ cut here ]------------
>>>> UBSAN: shift-out-of-bounds in drivers/i3c/master/dw-i3c-master.c:1592:21
>>>> usb 1-1: new high-speed USB device number 2 using xhci_hcd
>>>> shift exponent 18446744073709486145 is too large for 64-bit type 'long
>>>> unsigned int'
>>>> CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.18.0 #4
>>>> 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_common_probe.cold+0x16/0x1b
>>>> dw_i3c_probe+0x30/0x50
>>>> 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
>>>> bus_for_each_dev+0x8a/0xe0
>>>> driver_attach+0x1e/0x30
>>>> bus_add_driver+0x13e/0x230
>>>> ? __pfx_dw_i3c_driver_init+0x10/0x10
>>>> driver_register+0x75/0xf0
>>>> __platform_driver_register+0x1e/0x30
>>>> dw_i3c_driver_init+0x17/0x30
>>>> do_one_initcall+0x59/0x330
>>>> kernel_init_freeable+0x2bd/0x340
>>>> ? __pfx_kernel_init+0x10/0x10
>>>> kernel_init+0x1b/0x160
>>>> ? __pfx_kernel_init+0x10/0x10
>>>> ret_from_fork+0x202/0x230
>>>> ? __pfx_kernel_init+0x10/0x10
>>>> ret_from_fork_asm+0x1a/0x30
>>>> </TASK>
>>>> ---[ end trace ]---
>>>>
>>>>
>>>> --
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>>>> http://lists.infradead.org/mailman/listinfo/linux-i3c
>>
>>
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