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

K Prateek Nayak
2025-09-11T16:52:30Z

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));

--
Thanks and Regards,
Prateek