Re: [RFC PATCH v9 01/27] Documentation/x86: Add CET description

H.J. Lu
2020-03-09T23:11:42Z

On Mon, Mar 9, 2020 at 3:19 PM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 3/9/20 2:12 PM, H.J. Lu wrote:
> >> But what are the rules for clone()? Should there be rules for
> >> mismatches for CET enabling between threads if a process (not child
> >> processes)?
> > What did you mean? A threaded application is either CET enabled or not
> > CET enabled. A new thread from clone makes no difference.
>
> Stacks are fundamentally thread-local resources. The registers that
> point to them and MSRs that manage shadow stacks are all CPU-thread
> local. Nothing is fundamentally tied to the address space shared across
> the process.
>
> A thread might also share *no* control flow with its child. It might
> ask the thread to start in code that the parent can never even reach.
>
> It sounds like you've picked a Linux implementation that has
> restrictions on top of the fundamentals. That's not wrong per se, but
> it does deserve explanation and deliberate, not experimental design.
>
> Could you go back to the folks at Intel and try to figure out what this
> was designed to *do*? Yes, I'm probably one of those folks. You know
> where to find me. :)

A threaded application is loaded from disk. The object file on disk is
either CET enabled or not CET enabled.

--
H.J.