On 2025-08-23 12:39, Thomas Gleixner wrote:
> There is no point to read the critical section element in the newly
> registered user space RSEQ struct first in order to clear it.
>
> Just clear it and be done with it.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> ---
> kernel/rseq.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -492,11 +492,9 @@ void rseq_syscall(struct pt_regs *regs)
> /*
> * sys_rseq - setup restartable sequences for caller thread.
> */
> -SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len,
> - int, flags, u32, sig)
> +SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32, sig)
> {
> int ret;
> - u64 rseq_cs;
>
> if (flags & RSEQ_FLAG_UNREGISTER) {
> if (flags & ~RSEQ_FLAG_UNREGISTER)
> @@ -557,11 +555,9 @@ SYSCALL_DEFINE4(rseq, struct rseq __user
> * avoid a potential segfault on return to user-space. The proper thing
> * to do would have been to fail the registration but this would break
> * older libcs that reuse the rseq area for new threads without
> - * clearing the fields.
> + * clearing the fields. Don't bother reading it, just reset it.
> */
> - if (rseq_get_rseq_cs_ptr_val(rseq, &rseq_cs))
> - return -EFAULT;
> - if (rseq_cs && clear_rseq_cs(rseq))
> + if (put_user_masked_u64(0UL, &rseq->rseq_cs))
> return -EFAULT;
>
> #ifdef CONFIG_DEBUG_RSEQ
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com