Re: [PATCHv5 bpf-next 6/8] x86/shstk: Add return uprobe support

Oleg Nesterov
2024-05-15T15:28:08Z

On 05/15, Jiri Olsa wrote:
>
> On Wed, May 15, 2024 at 01:19:20PM +0200, Oleg Nesterov wrote:
> > Let me ask a couple of really stupid questions. What if the shadow stack
> > is "shorter" than the normal stack? I mean,
> >
> > enable_shstk()
> > {
> > prctl(ARCH_SHSTK_SHSTK);

I meant ARCH_SHSTK_ENABLE, of course

> > }
> >
> > what happens when enable_shstk() returns?
>
> I think it will crash, there's explanation in the comment in
> tools/testing/selftests/x86/test_shadow_stack.c test

OK, thanks...

But test_shadow_stack.c doesn't do ARCH_PRCTL(ARCH_SHSTK_DISABLE) if
all the tests succeed ? Confused but nevermind.

> > And what is the purpose of fpregs_lock_and_load() ? Why do we need to
> > fpregs_restore_userregs() in shstk_setup() and other places?
> >
> > Oleg.
> >
>