Re: [PATCH] x86/shstk: Provide kernel command line knob to disable

[Mathias Krause]

On 02.04.26 18:53, Edgecombe, Rick P wrote:
> On Thu, 2026-04-02 at 18:04 +0200, Peter Zijlstra wrote:
>>> However, in at least one case the UEFI firmware was involved and I
>>> had to test&debug on bare metal. Having such a knob allows ruling
>>> out or pin-pointing CET as the cause more easily.
>>
>> Fair enough, although this should probably have made it in the
>> Changelog.
>>
>> Other than that, 
> 
> Some firmwares use supervisor shadow stack in SMM and have had issues
> with CR4.CET set. But these were BIOS crashes.

TIL! :D

> 
> The other usefulness could be recovering from shadow stack crashes in
> early userspace that block boot.

Jepp. A chicken-bit is always nice to have, IMHO.

> 
> Acked-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> 
> Could we add something to the docs though?

As the 'ibt=off' commandline option lacks documentation as well, I don't
think it's needed.

There are other parameters, e.g. "debug-alternative", that are useful
debugging tools but also lack documentation. The reason for that is
likely that these switches are meant for developers and these can 'git
grep -w __setup' easily to hunt for these.

Thanks,
Mathias