Re: [PATCH v2 5/7] rust: file: add `Kuid` wrapper

[Peter Zijlstra]

On Fri, Dec 08, 2023 at 10:18:47AM -0800, Kees Cook wrote:

> Even if we look at the prerequisites for mounting an attack here, we've
> already got things in place to help mitigate arbitrary code execution
> (KCFI, BTI, etc). Nothing is perfect, but speculation gadgets are
> pretty far down on the list of concerns, IMO. We have no real x86 ROP
> defense right now in the kernel, so that's a much lower hanging fruit
> for attackers.

Supervisor shadow stacks, as they exist today, just can't work on Linux.
Should get fixed with FRED, but yeah, this is all somewhat unfortunate.

> As another comparison, on x86 there are so many direct execution gadgets
> present in middle-of-instruction code patterns that worrying about a
> speculation gadget seems silly to me.

FineIBT (or even IBT) limits the middle of function gadgets
significantly.