Re: [RFC PATCH 5/5] selftest/x86: Add CET quick test

Yu-cheng Yu
2020-05-21T23:23:35Z

On Thu, 2020-05-21 at 16:02 -0700, Kees Cook wrote:
> On Thu, May 21, 2020 at 02:17:20PM -0700, Yu-cheng Yu wrote:
> > Introduce a quick test to verify shadow stack and IBT are working.
>
> Cool! :)
>
> I'd love to see either more of a commit log or more comments in the test
> code itself. I had to spend a bit of time trying to understand how the
> test was working. (i.e. using ucontext to "reset", using segv handler to
> catch some of them, etc.) I have not yet figured out why you need to
> send USR1/USR2 for two of them instead of direct calls?

Yes, I will work on it.

[...]

> > +
> > +#pragma GCC push_options
> > +#pragma GCC optimize ("O0")
>
> Can you avoid compiler-specific pragmas? (Or verify that Clang also
> behaves correctly here?) Maybe it's better to just build the entire file
> with -O0 in the Makefile?

This file is compiled using -O2 in the makefile. I will see if other ways are
possible.

[...]

> > +
> > +void segv_handler(int signum, siginfo_t *si, void *uc)
> > +{
>
> Does anything in siginfo_t indicate which kind of failure you're
> detecting? It'd be nice to verify test_id matches the failure mode being
> tested.

Yes, there is an si_code for control-protection fault.
I will fix this.

Agree with your other comments.

Thanks,
Yu-cheng