Re: [PATCH 00/35] Shadow stacks for userspace

Edgecombe, Rick P
2022-06-01T17:24:37Z

On Wed, 2022-06-01 at 11:06 +0300, Mike Rapoport wrote:
> > Yea, having something working is really great. My only hesitancy is
> > that, per a discussion on the LAM patchset, we are going to make
> > this
> > enabling API CET only (same semantics for though). I suppose the
> > locking API arch_prctl() could still be support other arch
> > features,
> > but it might be a second CET only regset. It's not the end of the
> > world.
>
> The support for CET in criu is anyway experimental for now, if the
> kernel
> API will be slightly different in the end, we'll update criu.
> The important things are the ability to control tracee shadow stack
> from ptrace, the ability to map the shadow stack at fixed address and
> the
> ability to control the features at least from ptrace.
> As long as we have APIs that provide those, it should be Ok.
>
> > I guess the other consideration is tieing CRIU to glibc
> > peculiarities.
> > Like even if we fix glibc, then CRIU may not work with some other
> > libc
> > or app that force disables for some weird reason. Is it supposed to
> > be
> > libc-agnostic?
>
> Actually using the ptrace to control the CET features does not tie
> criu to
> glibc. The current proposal for the arch_prctl() allows libc to lock
> CET
> features and having a ptrace call to control the lock makes criu
> agnostic
> to libc behaviour.

From staring at the glibc code, I'm suspicious something was weird with
your test setup, as I don't think it should be locking. But I guess to
be completely proper you would need to save and restore the lock state
anyway. So, ok yea, on balance probably better to have an extra
interface.

Should we make it a GET/SET interface?