[PATCH v4 19/35] random: vDSO: only access vDSO datapage after random_init()

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

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@linutronix.de>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
---
 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 73c53a4fb949bfd2ed723fa3cec3fe0d066a7fa3..f39524fb076a0c77bab228d4f2d45fee37291eb0 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));
 

-- 
2.51.0