linux-kernel - [tip: timers/vdso] random: vDSO: Only access vDSO datapage after random

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Message-ID: <176202647299.2601451.467843181214566256.tip-bot2@tip-bot2>
Date: Sat, 01 Nov 2025 19:47:52 -0000
From: tip-bot2 for Thomas Weißschuh <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: thomas.weissschuh@...utronix.de, Thomas Gleixner <tglx@...utronix.de>,
 Andreas Larsson <andreas@...sler.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/vdso] random: vDSO: Only access vDSO datapage after
 random_init()

The following commit has been merged into the timers/vdso branch of tip:

Commit-ID:     e5ec11b3da6d37dc2150007b34afca871c6b8fb4
Gitweb:        https://git.kernel.org/tip/e5ec11b3da6d37dc2150007b34afca871c6b8fb4
Author:        Thomas Weißschuh <thomas.weissschuh@...utronix.de>
AuthorDate:    Tue, 14 Oct 2025 08:49:05 +02:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Sat, 01 Nov 2025 20:44:05 +01:00

random: vDSO: Only access vDSO datapage after random_init()

Upcoming changes to the generic vDSO library will mean that the vDSO
datapage will not yet be usable during early boot.

Introduce a static key which prevents early accesses.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Andreas Larsson <andreas@...sler.com>
Reviewed-by: Andreas Larsson <andreas@...sler.com>
Link: https://patch.msgid.link/20251014-vdso-sparc64-generic-2-v4-19-e0607bf49dea@linutronix.de
---
 drivers/char/random.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 73c53a4..f39524f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -88,6 +88,7 @@ static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
 static struct fasync_struct *fasync;
 static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
+static DEFINE_STATIC_KEY_FALSE(random_vdso_is_ready);
 
 /* Control how we warn userspace. */
 static struct ratelimit_state urandom_warning =
@@ -252,6 +253,9 @@ static void random_vdso_update_generation(unsigned long next_gen)
 	if (!IS_ENABLED(CONFIG_VDSO_GETRANDOM))
 		return;
 
+	if (!static_branch_likely(&random_vdso_is_ready))
+		return;
+
 	/* base_crng.generation's invalid value is ULONG_MAX, while
 	 * vdso_k_rng_data->generation's invalid value is 0, so add one to the
 	 * former to arrive at the latter. Use smp_store_release so that this
@@ -274,6 +278,9 @@ static void random_vdso_set_ready(void)
 	if (!IS_ENABLED(CONFIG_VDSO_GETRANDOM))
 		return;
 
+	if (!static_branch_likely(&random_vdso_is_ready))
+		return;
+
 	WRITE_ONCE(vdso_k_rng_data->is_ready, true);
 }
 
@@ -925,6 +932,9 @@ void __init random_init(void)
 	_mix_pool_bytes(&entropy, sizeof(entropy));
 	add_latent_entropy();
 
+	if (IS_ENABLED(CONFIG_VDSO_GETRANDOM))
+		static_branch_enable(&random_vdso_is_ready);
+
 	/*
 	 * If we were initialized by the cpu or bootloader before jump labels
 	 * or workqueues are initialized, then we should enable the static
@@ -934,8 +944,10 @@ void __init random_init(void)
 		crng_set_ready(NULL);
 
 	/* Reseed if already seeded by earlier phases. */
-	if (crng_ready())
+	if (crng_ready()) {
 		crng_reseed(NULL);
+		random_vdso_set_ready();
+	}
 
 	WARN_ON(register_pm_notifier(&pm_notifier));