Re: [PATCH] x86/entry/32: Harden return-to-user

[Dave Hansen]

On 10/28/26 12:21, s1nkhole wrote:
> If you have a moment: this is my first work on arch/x86, and I would like
> to contribute something that is actually useful. Is there a small task
> in x86/entry or in kernel hardening that you would suggest as a better
> starting point, or a place where help with testing or review would be
> welcome? I can build and run kernels under QEMU.

It's not small, but kernel shadow stacks are an _incredibly_ powerful
hardening tool. You can buy a system off the shelf that sanely supports
them (including FRED), but the kernel doesn't support them yet.

My current work in progress is here:

> https://git.kernel.org/pub/scm/linux/kernel/git/daveh/devel.git/log/?h=kss-2026-10-23

Another set of eyes on that would be nice. Although I do think I'm going
to abandon tacking the shadow stack on to the thread_union for now. So I
don't suggest looking at it too deeply until I get another version out
the door.

One thing you could do today is go into the list in here:

> https://git.kernel.org/pub/scm/linux/kernel/git/daveh/devel.git/commit/?h=kss-2026-10-21&id=4dab5fe58904ee07b3622f25bbe3c1b7ff820bf5

and pick a feature or two and figure out if they need fixing for shadow
stacks or not, and if so what a fix might look like.

Or another set of eyes on this:

> https://git.kernel.org/pub/scm/linux/kernel/git/daveh/devel.git/log/?h=taskfun-2026-10-26

It's ready to post but I'm just waiting for the merge window to close.