linux-kernel - [PATCH v2 16/25] timekeeping: Rework do_settimeofday64() to use shadow

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: <20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-16-554456a44a15@linutronix.de>
Date: Wed, 09 Oct 2024 10:29:09 +0200
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: John Stultz <jstultz@...gle.com>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Miroslav Lichvar <mlichvar@...hat.com>, 
 Richard Cochran <richardcochran@...il.com>, 
 Christopher S Hall <christopher.s.hall@...el.com>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH v2 16/25] timekeeping: Rework do_settimeofday64() to use
 shadow_timekeeper

From: Anna-Maria Behnsen <anna-maria@...utronix.de>

Updates of the timekeeper can be done by operating on the shadow timekeeper
and afterwards copying the result into the real timekeeper. This has the
advantage, that the sequence count write protected region is kept as small
as possible.

Convert do_settimeofday64() to use this scheme.

That allows to use a scoped_guard() for locking the timekeeper lock as the
usage of the shadow timekeeper allows a rollback in the error case instead
of the full timekeeper update of the original code.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/time/timekeeping.c | 42 ++++++++++++++++--------------------------
 1 file changed, 16 insertions(+), 26 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 41d88f645868..cc01ad53d96d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1479,45 +1479,35 @@ EXPORT_SYMBOL_GPL(timekeeping_clocksource_has_base);
  */
 int do_settimeofday64(const struct timespec64 *ts)
 {
-	struct timekeeper *tk = &tk_core.timekeeper;
 	struct timespec64 ts_delta, xt;
-	unsigned long flags;
-	int ret = 0;
 
 	if (!timespec64_valid_settod(ts))
 		return -EINVAL;
 
-	raw_spin_lock_irqsave(&tk_core.lock, flags);
-	write_seqcount_begin(&tk_core.seq);
-
-	timekeeping_forward_now(tk);
-
-	xt = tk_xtime(tk);
-	ts_delta = timespec64_sub(*ts, xt);
+	scoped_guard (raw_spinlock_irqsave, &tk_core.lock) {
+		struct timekeeper *tk = &tk_core.shadow_timekeeper;
 
-	if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
-		ret = -EINVAL;
-		goto out;
-	}
+		timekeeping_forward_now(tk);
 
-	tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));
+		xt = tk_xtime(tk);
+		ts_delta = timespec64_sub(*ts, xt);
 
-	tk_set_xtime(tk, ts);
-out:
-	timekeeping_update(&tk_core, tk, TK_UPDATE_ALL | TK_MIRROR);
+		if (timespec64_compare(&tk->wall_to_monotonic, &ts_delta) > 0) {
+			timekeeping_restore_shadow(&tk_core);
+			return -EINVAL;
+		}
 
-	write_seqcount_end(&tk_core.seq);
-	raw_spin_unlock_irqrestore(&tk_core.lock, flags);
+		tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, ts_delta));
+		tk_set_xtime(tk, ts);
+		timekeeping_update_staged(&tk_core, TK_UPDATE_ALL);
+	}
 
 	/* Signal hrtimers about time change */
 	clock_was_set(CLOCK_SET_WALL);
 
-	if (!ret) {
-		audit_tk_injoffset(ts_delta);
-		add_device_randomness(ts, sizeof(*ts));
-	}
-
-	return ret;
+	audit_tk_injoffset(ts_delta);
+	add_device_randomness(ts, sizeof(*ts));
+	return 0;
 }
 EXPORT_SYMBOL(do_settimeofday64);
 

-- 
2.39.5