Re: kernel NULL pointer dereference in quirk_clear_strap_no_soft_reset_dev2_f0 -> amd_smn_read

[Mario Limonciello <mario.limonciello@amd.com>]

On 6/5/26 12:34, Marek Marczykowski-Górecki wrote:
> On Mon, Jan 12, 2026 at 08:47:50PM -0600, Mario Limonciello wrote:
>>
>>
>> On 1/12/2026 7:01 PM, Marek Marczykowski-Górecki wrote:
>>> Hi,
>>>
>>> I've got a report that kernel 6.17.9 crashes when running a Xen HVM domU
>>> with AMD Raphael/Granite Ridge USB controller passed through.
>>> It worked correctly in 6.12.59. Between those versions, I don't see any
>>> relevant change to quirk_clear_strap_no_soft_reset_dev2_f0() function,
>>> but the AMD node driver did got some changes, so my guess is one of them
>>> is to blame. I know the good-bad range is huge, but there aren't that
>>> many changes to the AMD node driver in this range.
>>
>> Is this perhaps a case that only the USB controller was passed through but
>> that the root controller wasn't?  That would lead to a case that
>> amd_smn_init() was never called and thus amd_roots was not initialized
>> properly.
>>
>> So it would be a NULL pointer deref.  If that's correct, something like this
>> should work to avoid it.
>>
>> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
>> index 3d0a4768d603c..894823b444d47 100644
>> --- a/arch/x86/kernel/amd_node.c
>> +++ b/arch/x86/kernel/amd_node.c
>> @@ -91,6 +91,11 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32
>> address, u32 *value, b
>>          if (node >= amd_num_nodes())
>>                  return err;
>>
>> +       if (!amd_roots) {
>> +               pr_warn("AMD SMN roots not initialized.\n");
>> +               return err;
>> +       }
>> +
>>          root = amd_roots[node];
>>          if (!root)
>>                  return err;
> 
> Thanks, I finally got confirmation from affected user that this patch
> fixes the issue. From what I understand, adbf61cc47cb ("x86/acpi/boot: Correct
> acpi_is_processor_usable() check again") was not enough.
> 
>>> Original report at (with full kernel log etc): https://forum.qubes-os.org/t/yet-another-usb-keyboard-thread/38355/8
> 

There's another patch being discussed.  Could this help?

https://lore.kernel.org/all/20260602184823.GKah8ld2QJLm28xoa9@fat_crate.local/