Re: [patch 05/12] rseq: Add prctl() to enable time slice extensions

[Mathieu Desnoyers]

On 2025-09-11 12:52, K Prateek Nayak wrote:
> Hello Mathieu,
>
> On 9/11/2025 9:20 PM, Mathieu Desnoyers wrote:
> > >    +int rseq_slice_extension_prctl(unsigned long arg2, unsigned long arg3)
> > > +{
> > > +    switch (arg2) {
> > > +    case PR_RSEQ_SLICE_EXTENSION_GET:
> > > +        if (arg3)
> > > +            return -EINVAL;
> > > +        return current->rseq.slice.state.enabled ? PR_RSEQ_SLICE_EXT_ENABLE : 0;
> > > +
> > > +    case PR_RSEQ_SLICE_EXTENSION_SET: {
> > > +        u32 rflags, valid = RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
> > > +        bool enable = !!(arg3 & PR_RSEQ_SLICE_EXT_ENABLE);
> > > +
> > > +        if (arg3 & ~PR_RSEQ_SLICE_EXT_ENABLE)
> > > +            return -EINVAL;
> > > +        if (!rseq_slice_extension_enabled())
> > > +            return -ENOTSUPP;
> > > +        if (!current->rseq.usrptr)
> > > +            return -ENXIO;
> > > +
> > > +        /* No change? */
> > > +        if (enable == !!current->rseq.slice.state.enabled)
> > > +            return 0;
> > > +
> > > +        if (get_user(rflags, &current->rseq.usrptr->flags))
> > > +            goto die;
> > > +
> > > +        if (current->rseq.slice.state.enabled)
> > > +            valid |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
> > > +
> > > +        if ((rflags & valid) != valid)
> > > +            goto die;
> > > +
> > > +        rflags &= ~RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
> > > +        rflags |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
> > > +        if (enable)
> > > +            rflags |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
> > > +
> > > +        if (put_user(rflags, &current->rseq.usrptr->flags))
> > > +            goto die;
> > > +
> > > +        current->rseq.slice.state.enabled = enable;
> >
> > What should happen to this enabled state if rseq is unregistered
> > after this prctl ?
>
> Wouldn't rseq_reset() deal with it since it does a:
>
>      memset(&t->rseq, 0, sizeof(t->rseq));

Good point, thanks!

Mathieu


--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com