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

Mathieu Desnoyers
2025-09-11T17:18:59Z

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.