random: remove mostly unused async readiness notifier

The register_random_ready_notifier() notifier is somewhat complicated,
and was already recently rewritten to use notifier blocks. It is only
used now by one consumer in the kernel, vsprintf.c, for which the async
mechanism is really overly complex for what it actually needs. This
commit removes register_random_ready_notifier() and unregister_random_
ready_notifier(), because it just adds complication with little utility,
and changes vsprintf.c to just check on `!rng_is_initialized() &&
!rng_has_arch_random()`, which will eventually be true. Performance-
wise, that code was already using a static branch, so there's basically
no overhead at all to this change.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Petr Mladek <pmladek@suse.com> # for vsprintf.c
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 6b8c89378954f7f9600a40b5f72ecaf78edfcc75..16b39d2dead78b4b8b78f5a58c58fd4c32f96829 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -84,8 +84,6 @@ static DEFINE_STATIC_KEY_FALSE(crng_is_ready);
 /* Various types of waiters for crng_init->CRNG_READY transition. */
 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
 static struct fasync_struct *fasync;
-static DEFINE_SPINLOCK(random_ready_chain_lock);
-static RAW_NOTIFIER_HEAD(random_ready_chain);
 
 /* Control how we warn userspace. */
 static struct ratelimit_state urandom_warning =
@@ -142,51 +140,6 @@ int wait_for_random_bytes(void)
 }
 EXPORT_SYMBOL(wait_for_random_bytes);
 
-/*
- * Add a callback function that will be invoked when the input
- * pool is initialised.
- *
- * returns: 0 if callback is successfully added
- *         -EALREADY if pool is already initialised (callback not called)
- */
-int __cold register_random_ready_notifier(struct notifier_block *nb)
-{
-       unsigned long flags;
-       int ret = -EALREADY;
-
-       if (crng_ready())
-               return ret;
-
-       spin_lock_irqsave(&random_ready_chain_lock, flags);
-       if (!crng_ready())
-               ret = raw_notifier_chain_register(&random_ready_chain, nb);
-       spin_unlock_irqrestore(&random_ready_chain_lock, flags);
-       return ret;
-}
-
-/*
- * Delete a previously registered readiness callback function.
- */
-int __cold unregister_random_ready_notifier(struct notifier_block *nb)
-{
-       unsigned long flags;
-       int ret;
-
-       spin_lock_irqsave(&random_ready_chain_lock, flags);
-       ret = raw_notifier_chain_unregister(&random_ready_chain, nb);
-       spin_unlock_irqrestore(&random_ready_chain_lock, flags);
-       return ret;
-}
-
-static void __cold process_random_ready_list(void)
-{
-       unsigned long flags;
-
-       spin_lock_irqsave(&random_ready_chain_lock, flags);
-       raw_notifier_call_chain(&random_ready_chain, 0, NULL);
-       spin_unlock_irqrestore(&random_ready_chain_lock, flags);
-}
-
 #define warn_unseeded_randomness() \
        if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
                printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
@@ -775,7 +728,6 @@ static void __cold _credit_init_bits(size_t bits)
        if (orig < POOL_READY_BITS && new >= POOL_READY_BITS) {
                crng_reseed(); /* Sets crng_init to CRNG_READY under base_crng.lock. */
                execute_in_process_context(crng_set_ready, &set_ready);
-               process_random_ready_list();
                wake_up_interruptible(&crng_init_wait);
                kill_fasync(&fasync, SIGIO, POLL_IN);
                pr_notice("crng init done\n");

diff --git a/include/linux/random.h b/include/linux/random.h
index 6af130c6edb91af5fadf28224fb48519c2965f49..d2360b2825b617acc34c4ecc26020c49aab6919f 100644 (file)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -78,8 +78,6 @@ int __init random_init(const char *command_line);
 bool rng_is_initialized(void);
 bool rng_has_arch_random(void);
 int wait_for_random_bytes(void);
-int register_random_ready_notifier(struct notifier_block *nb);
-int unregister_random_ready_notifier(struct notifier_block *nb);
 
 /* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
  * Returns the result of the call to wait_for_random_bytes. */

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 20e9887faaaa4a5eeaf37ab7911ed1cbafcb01ac..fb77f7bfd126b5fd7498ec6e979d6eefd9f07b5a 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -750,60 +750,38 @@ static int __init debug_boot_weak_hash_enable(char *str)
 }
 early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);
 
-static DEFINE_STATIC_KEY_TRUE(not_filled_random_ptr_key);
-static siphash_key_t ptr_key __read_mostly;
+static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
 
 static void enable_ptr_key_workfn(struct work_struct *work)
 {
-       get_random_bytes(&ptr_key, sizeof(ptr_key));
-       /* Needs to run from preemptible context */
-       static_branch_disable(&not_filled_random_ptr_key);
+       static_branch_enable(&filled_random_ptr_key);
 }
 
-static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
-
-static int fill_random_ptr_key(struct notifier_block *nb,
-                              unsigned long action, void *data)
-{
-       /* This may be in an interrupt handler. */
-       queue_work(system_unbound_wq, &enable_ptr_key_work);
-       return 0;
-}
-
-static struct notifier_block random_ready = {
-       .notifier_call = fill_random_ptr_key
-};
-
-static int __init initialize_ptr_random(void)
-{
-       int ret;
-
-       /* Don't bother waiting for RNG to be ready if RDRAND is mixed in already. */
-       if (rng_has_arch_random()) {
-               enable_ptr_key_workfn(&enable_ptr_key_work);
-               return 0;
-       }
-
-       ret = register_random_ready_notifier(&random_ready);
-       if (!ret) {
-               return 0;
-       } else if (ret == -EALREADY) {
-               /* This is in preemptible context */
-               enable_ptr_key_workfn(&enable_ptr_key_work);
-               return 0;
-       }
-
-       return ret;
-}
-early_initcall(initialize_ptr_random);
-
 /* Maps a pointer to a 32 bit unique identifier. */
 static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
 {
+       static siphash_key_t ptr_key __read_mostly;
        unsigned long hashval;
 
-       if (static_branch_unlikely(&not_filled_random_ptr_key))
-               return -EAGAIN;
+       if (!static_branch_likely(&filled_random_ptr_key)) {
+               static bool filled = false;
+               static DEFINE_SPINLOCK(filling);
+               static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
+               unsigned long flags;
+
+               if (!system_unbound_wq ||
+                   (!rng_is_initialized() && !rng_has_arch_random()) ||
+                   !spin_trylock_irqsave(&filling, flags))
+                       return -EAGAIN;
+
+               if (!filled) {
+                       get_random_bytes(&ptr_key, sizeof(ptr_key));
+                       queue_work(system_unbound_wq, &enable_ptr_key_work);
+                       filled = true;
+               }
+               spin_unlock_irqrestore(&filling, flags);
+       }
+
 
 #ifdef CONFIG_64BIT
        hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);