linux-kernel - [tip: sched/core] rseq: Allow registering RSEQ with slice extension

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <176907693970.510.5602511824863257539.tip-bot2@tip-bot2>
Date: Thu, 22 Jan 2026 10:15:39 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: sched/core] rseq: Allow registering RSEQ with slice extension

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

Commit-ID:     d6200245c75e832af2087bc60ba2e6641a90eee9
Gitweb:        https://git.kernel.org/tip/d6200245c75e832af2087bc60ba2e6641a90eee9
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 19 Jan 2026 11:23:57 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 22 Jan 2026 11:11:19 +01:00

rseq: Allow registering RSEQ with slice extension

Since glibc cares about the number of syscalls required to initialize a new
thread, allow initializing rseq with slice extension on. This avoids having to
do another prctl().

Requested-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20260121143207.814193010@infradead.org
---
 include/uapi/linux/rseq.h |  3 ++-
 kernel/rseq.c             | 12 ++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 6afc219..863c4a0 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -19,7 +19,8 @@ enum rseq_cpu_id_state {
 };
 
 enum rseq_flags {
-	RSEQ_FLAG_UNREGISTER = (1 << 0),
+	RSEQ_FLAG_UNREGISTER			= (1 << 0),
+	RSEQ_FLAG_SLICE_EXT_DEFAULT_ON		= (1 << 1),
 };
 
 enum rseq_cs_flags_bit {
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 275d701..1c5490a 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -424,7 +424,7 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
 		return 0;
 	}
 
-	if (unlikely(flags))
+	if (unlikely(flags & ~(RSEQ_FLAG_SLICE_EXT_DEFAULT_ON)))
 		return -EINVAL;
 
 	if (current->rseq.usrptr) {
@@ -459,8 +459,12 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
 	if (!access_ok(rseq, rseq_len))
 		return -EFAULT;
 
-	if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION))
+	if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSION)) {
 		rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE;
+		if (rseq_slice_extension_enabled() &&
+		    (flags & RSEQ_FLAG_SLICE_EXT_DEFAULT_ON))
+			rseqfl |= RSEQ_CS_FLAG_SLICE_EXT_ENABLED;
+	}
 
 	scoped_user_write_access(rseq, efault) {
 		/*
@@ -488,6 +492,10 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
 	current->rseq.len = rseq_len;
 	current->rseq.sig = sig;
 
+#ifdef CONFIG_RSEQ_SLICE_EXTENSION
+	current->rseq.slice.state.enabled = !!(rseqfl & RSEQ_CS_FLAG_SLICE_EXT_ENABLED);
+#endif
+
 	/*
 	 * If rseq was previously inactive, and has just been
 	 * registered, ensure the cpu_id_start and cpu_id fields