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

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Message-ID: <176224425825.2601451.15206634611280288656.tip-bot2@tip-bot2>
Date: Tue, 04 Nov 2025 08:17:38 -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>,
 Ingo Molnar <mingo@...nel.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:     067b3b41b4dd5bf51d6874206f5c1f72e0684eeb
Gitweb:        https://git.kernel.org/tip/067b3b41b4dd5bf51d6874206f5c1f72e0684eeb
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Mon, 27 Oct 2025 09:44:24 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 04 Nov 2025 08:30:05 +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>
Signed-off-by: Ingo Molnar <mingo@...nel.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