linux-kernel - [tip: core/rseq] rseq: Simplify registration

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Message-ID: <176173343815.2601451.9368028900741069432.tip-bot2@tip-bot2>
Date: Wed, 29 Oct 2025 10:23:58 -0000
From: "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: core/rseq] rseq: Simplify registration

The following commit has been merged into the core/rseq branch of tip:

Commit-ID:     bd88944825d9579d1240dcc55b5f57635298a121
Gitweb:        https://git.kernel.org/tip/bd88944825d9579d1240dcc55b5f57635298a121
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Mon, 27 Oct 2025 09:44:24 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 29 Oct 2025 11:07:12 +01:00

rseq: Simplify registration

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@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Link: https://patch.msgid.link/20251027084306.274661227@linutronix.de
---
 kernel/rseq.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index 51fafc4..80af48a 100644
--- 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 *, rseq, u32, rseq_len,
 	 * 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(0UL, &rseq->rseq_cs))
 		return -EFAULT;
 
 #ifdef CONFIG_DEBUG_RSEQ