linux-kernel - [PATCH] timer_list: Don't use %pK through printk

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Message-Id: <20250311-restricted-pointers-timer-v1-1-6626b91e54ab@linutronix.de>
Date: Tue, 11 Mar 2025 10:54:47 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH] timer_list: Don't use %pK through printk

This reverts
commit f590308536db ("timer debug: Hide kernel addresses via %pK in /proc/timer_list")

SEQ_printf() either uses the real seq_printf() to write implement a virtual
file or vprintk() to print to the kernel log.
In the past %pK was preferable to %p as it would not leak raw pointer
values into the kernel log.
Since commit ad67b74d2469 ("printk: hash addresses printed with %p")
the regular %p has been improved to avoid this issue.
Furthermore, restricted pointers ("%pK") were never meant to be used
through printk(). They can still unintentionally leak raw pointers or
acquire sleeping looks in atomic contexts.

Switch to the regular pointer formatting which is safer, easier to reason
about and sufficient here.

Link: https://lore.kernel.org/lkml/20250113171731-dc10e3c1-da64-4af0-b767-7c7070468023@linutronix.de/
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 kernel/time/timer_list.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index 1c311c46da5074c1cb33027c96638e68a606574a..cfbb46cc4e7613a3d7255b67a941dd05387cf68e 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -46,7 +46,7 @@ static void
 print_timer(struct seq_file *m, struct hrtimer *taddr, struct hrtimer *timer,
 	    int idx, u64 now)
 {
-	SEQ_printf(m, " #%d: <%pK>, %ps", idx, taddr, timer->function);
+	SEQ_printf(m, " #%d: <%p>, %ps", idx, taddr, timer->function);
 	SEQ_printf(m, ", S:%02x", timer->state);
 	SEQ_printf(m, "\n");
 	SEQ_printf(m, " # expires at %Lu-%Lu nsecs [in %Ld to %Ld nsecs]\n",
@@ -98,7 +98,7 @@ print_active_timers(struct seq_file *m, struct hrtimer_clock_base *base,
 static void
 print_base(struct seq_file *m, struct hrtimer_clock_base *base, u64 now)
 {
-	SEQ_printf(m, "  .base:       %pK\n", base);
+	SEQ_printf(m, "  .base:       %p\n", base);
 	SEQ_printf(m, "  .index:      %d\n", base->index);
 
 	SEQ_printf(m, "  .resolution: %u nsecs\n", hrtimer_resolution);

---
base-commit: 4d872d51bc9d7b899c1f61534e3dbde72613f627
change-id: 20250311-restricted-pointers-timer-f169f21c3838

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@...utronix.de>