Re: [patch 01/10] rseq: Set rseq::cpu_id_start to 0 on unregistration

Dmitry Vyukov
2026-04-29T08:21:09Z

On Wed, 29 Apr 2026 at 01:33, Thomas Gleixner <tglx@kernel.org> wrote:
>
> The RSEQ rework changed that to RSEQ_CPU_UNINITILIZED, which is obviously
> incompatible. Revert back to the original behavior.
>
> Fixes: 0f085b41880e ("rseq: Provide and use rseq_set_ids()")
> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> Cc: stable@vger.kernel.org

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

> ---
> kernel/rseq.c | 20 +++++++++-----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -236,11 +236,6 @@ static int __init rseq_debugfs_init(void
> }
> __initcall(rseq_debugfs_init);
>
> -static bool rseq_set_ids(struct task_struct *t, struct rseq_ids *ids, u32 node_id)
> -{
> - return rseq_set_ids_get_csaddr(t, ids, node_id, NULL);
> -}
> -
> static bool rseq_handle_cs(struct task_struct *t, struct pt_regs *regs)
> {
> struct rseq __user *urseq = t->rseq.usrptr;
> @@ -384,19 +379,22 @@ void rseq_syscall(struct pt_regs *regs)
>
> static bool rseq_reset_ids(void)
> {
> - struct rseq_ids ids = {
> - .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
> - .mm_cid = 0,
> - };
> + struct rseq __user *rseq = current->rseq.usrptr;
>
> /*
> * If this fails, terminate it because this leaves the kernel in
> * stupid state as exit to user space will try to fixup the ids
> * again.
> */
> - if (rseq_set_ids(current, &ids, 0))
> - return true;
> + scoped_user_rw_access(rseq, efault) {
> + unsafe_put_user(0, &rseq->cpu_id_start, efault);
> + unsafe_put_user(RSEQ_CPU_ID_UNINITIALIZED, &rseq->cpu_id, efault);
> + unsafe_put_user(0, &rseq->node_id, efault);
> + unsafe_put_user(0, &rseq->mm_cid, efault);
> + }
> + return true;
>
> +efault:
> force_sig(SIGSEGV);
> return false;
> }
>