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
Wed Dec 10 11:50:24 PST 2025
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
[ 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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