[PATCH v2 00/10] random: re-group and re-document functions

[PATCH v2 00/10] random: re-group and re-document functions

[Jason A. Donenfeld]

We previously had massive documentation comments and functions strewn
all about. This attempts to restore sanity by dividing the code into a
few sections:

- Initialization and readiness waiting.
- Fast key erasure RNG.
- Entropy accumulation and extraction.
- Entropy collection.
- Userspace read/write.
- Sysctl.

The result of this ordering and this grouping is only 2 forward
declarations, indicating that this is probably a sensible grouping.
Also, some documentation that was just hopelessly out of date been
removed. We'll later look into re-adding parts of this to the Linux man
pages project.

No functional changes.

Jason A. Donenfeld (10):
  random: introduce drain_entropy() helper to declutter crng_reseed()
  random: remove useless header comment
  random: remove whitespace and reorder includes
  random: group initialization wait functions
  random: group crng functions
  random: group entropy extraction functions
  random: group entropy collection functions
  random: group userspace read/write functions
  random: group sysctl functions
  random: rewrite header introductory comment

 drivers/char/random.c  | 1899 ++++++++++++++++++++--------------------
 include/linux/random.h |    6 +-
 2 files changed, 950 insertions(+), 955 deletions(-)

-- 
2.35.0

[PATCH v2 01/10] random: introduce drain_entropy() helper to declutter crng_reseed()

[Jason A. Donenfeld]

In preparation for separating responsibilities, break out the entropy
count management part of crng_reseed() into its own function.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 44a20a1a1b3a..436b146b33be 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -260,6 +260,7 @@ static struct {
 };
 
 static void extract_entropy(void *buf, size_t nbytes);
+static bool drain_entropy(void *buf, size_t nbytes);
 
 static void crng_reseed(void);
 
@@ -453,22 +454,13 @@ static void crng_slow_load(const void *cp, size_t len)
 static void crng_reseed(void)
 {
 	unsigned long flags;
-	int entropy_count;
 	unsigned long next_gen;
 	u8 key[CHACHA_KEY_SIZE];
 	bool finalize_init = false;
 
-	/* First we make sure we have POOL_MIN_BITS of entropy in the pool,
-	 * and then we drain all of it. Only then can we extract a new key.
-	 */
-	do {
-		entropy_count = READ_ONCE(input_pool.entropy_count);
-		if (entropy_count < POOL_MIN_BITS)
-			return;
-	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
-	extract_entropy(key, sizeof(key));
-	wake_up_interruptible(&random_write_wait);
-	kill_fasync(&fasync, SIGIO, POLL_OUT);
+	/* Only reseed if we can, to prevent brute forcing a small amount of new bits. */
+	if (!drain_entropy(key, sizeof(key)))
+		return;
 
 	/* We copy the new key into the base_crng, overwriting the old one,
 	 * and update the generation counter. We avoid hitting ULONG_MAX,
@@ -893,6 +885,25 @@ static void extract_entropy(void *buf, size_t nbytes)
 	memzero_explicit(&block, sizeof(block));
 }
 
+/*
+ * First we make sure we have POOL_MIN_BITS of entropy in the pool,
+ * and then we drain all of it. Only then can we extract a new key
+ * with extract_entropy().
+ */
+static bool drain_entropy(void *buf, size_t nbytes)
+{
+	unsigned int entropy_count;
+	do {
+		entropy_count = READ_ONCE(input_pool.entropy_count);
+		if (entropy_count < POOL_MIN_BITS)
+			return false;
+	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
+	extract_entropy(buf, nbytes);
+	wake_up_interruptible(&random_write_wait);
+	kill_fasync(&fasync, SIGIO, POLL_OUT);
+	return true;
+}
+
 #define warn_unseeded_randomness(previous) \
 	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
 
-- 
2.35.0

Re: [PATCH v2 01/10] random: introduce drain_entropy() helper to declutter crng_reseed()

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:09PM +0100, Jason A. Donenfeld wrote:
> In preparation for separating responsibilities, break out the entropy
> count management part of crng_reseed() into its own function.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 35 +++++++++++++++++++++++------------
>  1 file changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 44a20a1a1b3a..436b146b33be 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -260,6 +260,7 @@ static struct {
>  };
>  
>  static void extract_entropy(void *buf, size_t nbytes);
> +static bool drain_entropy(void *buf, size_t nbytes);
>  
>  static void crng_reseed(void);
>  
> @@ -453,22 +454,13 @@ static void crng_slow_load(const void *cp, size_t len)
>  static void crng_reseed(void)
>  {
>  	unsigned long flags;
> -	int entropy_count;
>  	unsigned long next_gen;
>  	u8 key[CHACHA_KEY_SIZE];
>  	bool finalize_init = false;
>  
> -	/* First we make sure we have POOL_MIN_BITS of entropy in the pool,
> -	 * and then we drain all of it. Only then can we extract a new key.
> -	 */
> -	do {
> -		entropy_count = READ_ONCE(input_pool.entropy_count);
> -		if (entropy_count < POOL_MIN_BITS)
> -			return;
> -	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
> -	extract_entropy(key, sizeof(key));
> -	wake_up_interruptible(&random_write_wait);
> -	kill_fasync(&fasync, SIGIO, POLL_OUT);
> +	/* Only reseed if we can, to prevent brute forcing a small amount of new bits. */
> +	if (!drain_entropy(key, sizeof(key)))
> +		return;
>  
>  	/* We copy the new key into the base_crng, overwriting the old one,
>  	 * and update the generation counter. We avoid hitting ULONG_MAX,
> @@ -893,6 +885,25 @@ static void extract_entropy(void *buf, size_t nbytes)
>  	memzero_explicit(&block, sizeof(block));
>  }
>  
> +/*
> + * First we make sure we have POOL_MIN_BITS of entropy in the pool,
> + * and then we drain all of it. Only then can we extract a new key
> + * with extract_entropy().
> + */
> +static bool drain_entropy(void *buf, size_t nbytes)
> +{
> +	unsigned int entropy_count;
> +	do {
> +		entropy_count = READ_ONCE(input_pool.entropy_count);
> +		if (entropy_count < POOL_MIN_BITS)
> +			return false;
> +	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
> +	extract_entropy(buf, nbytes);
> +	wake_up_interruptible(&random_write_wait);
> +	kill_fasync(&fasync, SIGIO, POLL_OUT);
> +	return true;
> +}

Looks good, but perhaps the comment should clarify that drain_entropy() doesn't
destroy the entropy in the pool, but rather just extracts it and zeroes out the
entropy counter?

- Eric

Re: [PATCH v2 01/10] random: introduce drain_entropy() helper to declutter crng_reseed()

[Jason A. Donenfeld]

On Mon, Feb 21, 2022 at 5:34 AM Eric Biggers <ebiggers@kernel.org> wrote:
> Looks good, but perhaps the comment should clarify that drain_entropy() doesn't
> destroy the entropy in the pool, but rather just extracts it and zeroes out the
> entropy counter?

Will do.

[PATCH v3] random: introduce drain_entropy() helper to declutter crng_reseed()

[Jason A. Donenfeld]

In preparation for separating responsibilities, break out the entropy
count management part of crng_reseed() into its own function.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
v3 adjusts the drain_entropy() comment to note that we're only setting
the entropy count to zero, per Eric's request.

 drivers/char/random.c | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index e5f8197dd49c..adc58914a7c0 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -260,6 +260,7 @@ static struct {
 };
 
 static void extract_entropy(void *buf, size_t nbytes);
+static bool drain_entropy(void *buf, size_t nbytes);
 
 static void crng_reseed(void);
 
@@ -456,23 +457,13 @@ static void crng_slow_load(const void *cp, size_t len)
 static void crng_reseed(void)
 {
 	unsigned long flags;
-	int entropy_count;
 	unsigned long next_gen;
 	u8 key[CHACHA_KEY_SIZE];
 	bool finalize_init = false;
 
-	/*
-	 * First we make sure we have POOL_MIN_BITS of entropy in the pool,
-	 * and then we drain all of it. Only then can we extract a new key.
-	 */
-	do {
-		entropy_count = READ_ONCE(input_pool.entropy_count);
-		if (entropy_count < POOL_MIN_BITS)
-			return;
-	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
-	extract_entropy(key, sizeof(key));
-	wake_up_interruptible(&random_write_wait);
-	kill_fasync(&fasync, SIGIO, POLL_OUT);
+	/* Only reseed if we can, to prevent brute forcing a small amount of new bits. */
+	if (!drain_entropy(key, sizeof(key)))
+		return;
 
 	/*
 	 * We copy the new key into the base_crng, overwriting the old one,
@@ -900,6 +891,25 @@ static void extract_entropy(void *buf, size_t nbytes)
 	memzero_explicit(&block, sizeof(block));
 }
 
+/*
+ * First we make sure we have POOL_MIN_BITS of entropy in the pool, and then we
+ * set the entropy count to zero (but don't actually touch any data). Only then
+ * can we extract a new key with extract_entropy().
+ */
+static bool drain_entropy(void *buf, size_t nbytes)
+{
+	unsigned int entropy_count;
+	do {
+		entropy_count = READ_ONCE(input_pool.entropy_count);
+		if (entropy_count < POOL_MIN_BITS)
+			return false;
+	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
+	extract_entropy(buf, nbytes);
+	wake_up_interruptible(&random_write_wait);
+	kill_fasync(&fasync, SIGIO, POLL_OUT);
+	return true;
+}
+
 #define warn_unseeded_randomness(previous) \
 	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
 
-- 
2.35.1

Re: [PATCH v3] random: introduce drain_entropy() helper to declutter crng_reseed()

[Eric Biggers]

On Mon, Feb 21, 2022 at 03:49:45PM +0100, Jason A. Donenfeld wrote:
> In preparation for separating responsibilities, break out the entropy
> count management part of crng_reseed() into its own function.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> v3 adjusts the drain_entropy() comment to note that we're only setting
> the entropy count to zero, per Eric's request.
> 
>  drivers/char/random.c | 36 +++++++++++++++++++++++-------------
>  1 file changed, 23 insertions(+), 13 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 02/10] random: remove useless header comment

[Jason A. Donenfeld]

This really adds nothing at all useful.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 include/linux/random.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/include/linux/random.h b/include/linux/random.h
index e92efb39779c..37e1e8c43d7e 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -1,9 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-/*
- * include/linux/random.h
- *
- * Include file for the random number generator.
- */
+
 #ifndef _LINUX_RANDOM_H
 #define _LINUX_RANDOM_H
 
-- 
2.35.0

Re: [PATCH v2 02/10] random: remove useless header comment

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:10PM +0100, Jason A. Donenfeld wrote:
> This really adds nothing at all useful.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  include/linux/random.h | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/linux/random.h b/include/linux/random.h
> index e92efb39779c..37e1e8c43d7e 100644
> --- a/include/linux/random.h
> +++ b/include/linux/random.h
> @@ -1,9 +1,5 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
> -/*
> - * include/linux/random.h
> - *
> - * Include file for the random number generator.
> - */
> +
>  #ifndef _LINUX_RANDOM_H
>  #define _LINUX_RANDOM_H
>  

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 03/10] random: remove whitespace and reorder includes

[Jason A. Donenfeld]

This is purely cosmetic. Future work involves figuring out which of
these headers we need and which we don't.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 436b146b33be..7bb18422705a 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -193,11 +193,10 @@
 #include <linux/syscalls.h>
 #include <linux/completion.h>
 #include <linux/uuid.h>
+#include <linux/uaccess.h>
 #include <crypto/chacha.h>
 #include <crypto/blake2s.h>
-
 #include <asm/processor.h>
-#include <linux/uaccess.h>
 #include <asm/irq.h>
 #include <asm/irq_regs.h>
 #include <asm/io.h>
-- 
2.35.0

Re: [PATCH v2 03/10] random: remove whitespace and reorder includes

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:11PM +0100, Jason A. Donenfeld wrote:
> This is purely cosmetic. Future work involves figuring out which of
> these headers we need and which we don't.
> 
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 436b146b33be..7bb18422705a 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -193,11 +193,10 @@
>  #include <linux/syscalls.h>
>  #include <linux/completion.h>
>  #include <linux/uuid.h>
> +#include <linux/uaccess.h>
>  #include <crypto/chacha.h>
>  #include <crypto/blake2s.h>
> -
>  #include <asm/processor.h>
> -#include <linux/uaccess.h>
>  #include <asm/irq.h>
>  #include <asm/irq_regs.h>
>  #include <asm/io.h>
> -- 

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 04/10] random: group initialization wait functions

[Jason A. Donenfeld]

This pulls all of the readiness waiting-focused functions into the first
labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 335 ++++++++++++++++++++++--------------------
 1 file changed, 174 insertions(+), 161 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7bb18422705a..499ad32e3060 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -201,44 +201,199 @@
 #include <asm/irq_regs.h>
 #include <asm/io.h>
 
-enum {
-	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
-	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
-};
-
-/*
- * Static global variables
- */
-static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
-static struct fasync_struct *fasync;
-
-static DEFINE_SPINLOCK(random_ready_list_lock);
-static LIST_HEAD(random_ready_list);
+/*********************************************************************
+ *
+ * Initialization and readiness waiting.
+ *
+ * Much of the RNG infrastructure is devoted to various dependencies
+ * being able to wait until the RNG has collected enough entropy and
+ * is ready for safe consumption.
+ *
+ *********************************************************************/
 
 /*
  * crng_init =  0 --> Uninitialized
  *		1 --> Initialized
  *		2 --> Initialized from input_pool
  *
- * crng_init is protected by primary_crng->lock, and only increases
+ * crng_init is protected by base_crng->lock, and only increases
  * its value (from 0->1->2).
  */
 static int crng_init = 0;
 #define crng_ready() (likely(crng_init > 1))
-static int crng_init_cnt = 0;
-static void process_random_ready_list(void);
-static void _get_random_bytes(void *buf, size_t nbytes);
+/* Various types of waiters for crng_init->2 transition. */
+static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
+static struct fasync_struct *fasync;
+static DEFINE_SPINLOCK(random_ready_list_lock);
+static LIST_HEAD(random_ready_list);
 
+/* Control how we warn userspace. */
 static struct ratelimit_state unseeded_warning =
 	RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
 static struct ratelimit_state urandom_warning =
 	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
-
 static int ratelimit_disable __read_mostly;
-
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
 
+/*
+ * Returns whether or not the urandom pool has been seeded and thus guaranteed
+ * to supply cryptographically secure random numbers. This applies to: the
+ * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
+ * ,u64,int,long} family of functions.
+ *
+ * Returns: true if the urandom pool has been seeded.
+ *          false if the urandom pool has not been seeded.
+ */
+bool rng_is_initialized(void)
+{
+	return crng_ready();
+}
+EXPORT_SYMBOL(rng_is_initialized);
+
+/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
+static void try_to_generate_entropy(void);
+
+/*
+ * Wait for the urandom pool to be seeded and thus guaranteed to supply
+ * cryptographically secure random numbers. This applies to: the /dev/urandom
+ * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
+ * family of functions. Using any of these functions without first calling
+ * this function forfeits the guarantee of security.
+ *
+ * Returns: 0 if the urandom pool has been seeded.
+ *          -ERESTARTSYS if the function was interrupted by a signal.
+ */
+int wait_for_random_bytes(void)
+{
+	if (likely(crng_ready()))
+		return 0;
+
+	do {
+		int ret;
+		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
+		if (ret)
+			return ret > 0 ? 0 : ret;
+
+		try_to_generate_entropy();
+	} while (!crng_ready());
+
+	return 0;
+}
+EXPORT_SYMBOL(wait_for_random_bytes);
+
+/*
+ * Add a callback function that will be invoked when the nonblocking
+ * pool is initialised.
+ *
+ * returns: 0 if callback is successfully added
+ *	    -EALREADY if pool is already initialised (callback not called)
+ *	    -ENOENT if module for callback is not alive
+ */
+int add_random_ready_callback(struct random_ready_callback *rdy)
+{
+	struct module *owner;
+	unsigned long flags;
+	int err = -EALREADY;
+
+	if (crng_ready())
+		return err;
+
+	owner = rdy->owner;
+	if (!try_module_get(owner))
+		return -ENOENT;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	if (crng_ready())
+		goto out;
+
+	owner = NULL;
+
+	list_add(&rdy->list, &random_ready_list);
+	err = 0;
+
+out:
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+
+	module_put(owner);
+
+	return err;
+}
+EXPORT_SYMBOL(add_random_ready_callback);
+
+/*
+ * Delete a previously registered readiness callback function.
+ */
+void del_random_ready_callback(struct random_ready_callback *rdy)
+{
+	unsigned long flags;
+	struct module *owner = NULL;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	if (!list_empty(&rdy->list)) {
+		list_del_init(&rdy->list);
+		owner = rdy->owner;
+	}
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+
+	module_put(owner);
+}
+EXPORT_SYMBOL(del_random_ready_callback);
+
+static void process_random_ready_list(void)
+{
+	unsigned long flags;
+	struct random_ready_callback *rdy, *tmp;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
+		struct module *owner = rdy->owner;
+
+		list_del_init(&rdy->list);
+		rdy->func(rdy);
+		module_put(owner);
+	}
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+}
+
+#define warn_unseeded_randomness(previous) \
+	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
+
+static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous)
+{
+#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
+	const bool print_once = false;
+#else
+	static bool print_once __read_mostly;
+#endif
+
+	if (print_once || crng_ready() ||
+	    (previous && (caller == READ_ONCE(*previous))))
+		return;
+	WRITE_ONCE(*previous, caller);
+#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
+	print_once = true;
+#endif
+	if (__ratelimit(&unseeded_warning))
+		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
+				func_name, caller, crng_init);
+}
+
+
+enum {
+	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
+	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
+};
+
+/*
+ * Static global variables
+ */
+static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
+static struct fasync_struct *fasync;
+
+static int crng_init_cnt = 0;
+static void _get_random_bytes(void *buf, size_t nbytes);
+
 /**********************************************************************
  *
  * OS independent entropy store.   Here are the functions which handle
@@ -319,22 +474,6 @@ static void fast_mix(u32 pool[4])
 	pool[2] = c;  pool[3] = d;
 }
 
-static void process_random_ready_list(void)
-{
-	unsigned long flags;
-	struct random_ready_callback *rdy, *tmp;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
-		struct module *owner = rdy->owner;
-
-		list_del_init(&rdy->list);
-		rdy->func(rdy);
-		module_put(owner);
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-}
-
 static void credit_entropy_bits(size_t nbits)
 {
 	unsigned int entropy_count, orig, add;
@@ -384,8 +523,6 @@ static DEFINE_PER_CPU(struct crng, crngs) = {
 	.lock = INIT_LOCAL_LOCK(crngs.lock),
 };
 
-static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
-
 /*
  * crng_fast_load() can be called by code in the interrupt service
  * path.  So we can't afford to dilly-dally. Returns the number of
@@ -903,29 +1040,6 @@ static bool drain_entropy(void *buf, size_t nbytes)
 	return true;
 }
 
-#define warn_unseeded_randomness(previous) \
-	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
-
-static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous)
-{
-#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
-	const bool print_once = false;
-#else
-	static bool print_once __read_mostly;
-#endif
-
-	if (print_once || crng_ready() ||
-	    (previous && (caller == READ_ONCE(*previous))))
-		return;
-	WRITE_ONCE(*previous, caller);
-#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
-	print_once = true;
-#endif
-	if (__ratelimit(&unseeded_warning))
-		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
-				func_name, caller, crng_init);
-}
-
 /*
  * This function is the exported kernel interface.  It returns some
  * number of good random numbers, suitable for key generation, seeding
@@ -1027,107 +1141,6 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-/*
- * Wait for the urandom pool to be seeded and thus guaranteed to supply
- * cryptographically secure random numbers. This applies to: the /dev/urandom
- * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
- * family of functions. Using any of these functions without first calling
- * this function forfeits the guarantee of security.
- *
- * Returns: 0 if the urandom pool has been seeded.
- *          -ERESTARTSYS if the function was interrupted by a signal.
- */
-int wait_for_random_bytes(void)
-{
-	if (likely(crng_ready()))
-		return 0;
-
-	do {
-		int ret;
-		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
-		if (ret)
-			return ret > 0 ? 0 : ret;
-
-		try_to_generate_entropy();
-	} while (!crng_ready());
-
-	return 0;
-}
-EXPORT_SYMBOL(wait_for_random_bytes);
-
-/*
- * Returns whether or not the urandom pool has been seeded and thus guaranteed
- * to supply cryptographically secure random numbers. This applies to: the
- * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
- * ,u64,int,long} family of functions.
- *
- * Returns: true if the urandom pool has been seeded.
- *          false if the urandom pool has not been seeded.
- */
-bool rng_is_initialized(void)
-{
-	return crng_ready();
-}
-EXPORT_SYMBOL(rng_is_initialized);
-
-/*
- * Add a callback function that will be invoked when the nonblocking
- * pool is initialised.
- *
- * returns: 0 if callback is successfully added
- *	    -EALREADY if pool is already initialised (callback not called)
- *	    -ENOENT if module for callback is not alive
- */
-int add_random_ready_callback(struct random_ready_callback *rdy)
-{
-	struct module *owner;
-	unsigned long flags;
-	int err = -EALREADY;
-
-	if (crng_ready())
-		return err;
-
-	owner = rdy->owner;
-	if (!try_module_get(owner))
-		return -ENOENT;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (crng_ready())
-		goto out;
-
-	owner = NULL;
-
-	list_add(&rdy->list, &random_ready_list);
-	err = 0;
-
-out:
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-
-	module_put(owner);
-
-	return err;
-}
-EXPORT_SYMBOL(add_random_ready_callback);
-
-/*
- * Delete a previously registered readiness callback function.
- */
-void del_random_ready_callback(struct random_ready_callback *rdy)
-{
-	unsigned long flags;
-	struct module *owner = NULL;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (!list_empty(&rdy->list)) {
-		list_del_init(&rdy->list);
-		owner = rdy->owner;
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-
-	module_put(owner);
-}
-EXPORT_SYMBOL(del_random_ready_callback);
-
 /*
  * This function will use the architecture-specific hardware random
  * number generator if it is available. It is not recommended for
-- 
2.35.0

Re: [PATCH v2 04/10] random: group initialization wait functions

[Dominik Brodowski]

> +/*
> + * Returns whether or not the urandom pool has been seeded and thus guaranteed
> + * to supply cryptographically secure random numbers. This applies to: the
> + * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
> + * ,u64,int,long} family of functions.
> + *
> + * Returns: true if the urandom pool has been seeded.
> + *          false if the urandom pool has not been seeded.

I think this comment should be updated, as there is no "urandom pool";
instead we should refer to the  "random pool" or the "random base pool".

> +/*
> + * Wait for the urandom pool to be seeded and thus guaranteed to supply
> + * cryptographically secure random numbers. This applies to: the /dev/urandom
> + * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
> + * family of functions. Using any of these functions without first calling
> + * this function forfeits the guarantee of security.
> + *
> + * Returns: 0 if the urandom pool has been seeded.
> + *          -ERESTARTSYS if the function was interrupted by a signal.

Same here.

> +/*
> + * Add a callback function that will be invoked when the nonblocking
> + * pool is initialised.

Same here ("nonblocking pool").

Other than that, looks fine.

Thanks,
	Dominik

Re: [PATCH v2 04/10] random: group initialization wait functions

[Jason A. Donenfeld]

Nice catch. Will unify these to be "input pool" since that's what
we're still calling it in the variables and elsewhere.

Re: [PATCH v2 04/10] random: group initialization wait functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:12PM +0100, Jason A. Donenfeld wrote:
> +/*
> + * Static global variables
> + */
> +static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
> +static struct fasync_struct *fasync;
> +
> +static int crng_init_cnt = 0;
> +static void _get_random_bytes(void *buf, size_t nbytes);

A couple oddities here:

  - 'fasync' is being defined twice.  It's already defined earlier in the file.
  - The prototype for _get_random_bytes() is unnecessary.

Other than that this patch looks good.

- Eric

Re: [PATCH v2 04/10] random: group initialization wait functions

[Jason A. Donenfeld]

On Mon, Feb 21, 2022 at 5:49 AM Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Sat, Feb 12, 2022 at 01:23:12PM +0100, Jason A. Donenfeld wrote:
> > +/*
> > + * Static global variables
> > + */
> > +static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
> > +static struct fasync_struct *fasync;
> > +
> > +static int crng_init_cnt = 0;
> > +static void _get_random_bytes(void *buf, size_t nbytes);
>
> A couple oddities here:
>
>   - 'fasync' is being defined twice.  It's already defined earlier in the file.
>   - The prototype for _get_random_bytes() is unnecessary.
>
> Other than that this patch looks good.

Nice catch, thanks. Will fix.

Jason

[PATCH v3] random: group initialization wait functions

[Jason A. Donenfeld]

This pulls all of the readiness waiting-focused functions into the first
labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
v3 removes the duplicate declarations for _get_random_bytes() and fasync.

 drivers/char/random.c | 333 ++++++++++++++++++++++--------------------
 1 file changed, 172 insertions(+), 161 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index ad112f928182..dd2da0b12350 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -201,44 +201,197 @@
 #include <asm/irq_regs.h>
 #include <asm/io.h>
 
-enum {
-	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
-	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
-};
-
-/*
- * Static global variables
- */
-static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
-static struct fasync_struct *fasync;
-
-static DEFINE_SPINLOCK(random_ready_list_lock);
-static LIST_HEAD(random_ready_list);
+/*********************************************************************
+ *
+ * Initialization and readiness waiting.
+ *
+ * Much of the RNG infrastructure is devoted to various dependencies
+ * being able to wait until the RNG has collected enough entropy and
+ * is ready for safe consumption.
+ *
+ *********************************************************************/
 
 /*
  * crng_init =  0 --> Uninitialized
  *		1 --> Initialized
  *		2 --> Initialized from input_pool
  *
- * crng_init is protected by primary_crng->lock, and only increases
+ * crng_init is protected by base_crng->lock, and only increases
  * its value (from 0->1->2).
  */
 static int crng_init = 0;
 #define crng_ready() (likely(crng_init > 1))
-static int crng_init_cnt = 0;
-static void process_random_ready_list(void);
-static void _get_random_bytes(void *buf, size_t nbytes);
+/* Various types of waiters for crng_init->2 transition. */
+static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
+static struct fasync_struct *fasync;
+static DEFINE_SPINLOCK(random_ready_list_lock);
+static LIST_HEAD(random_ready_list);
 
+/* Control how we warn userspace. */
 static struct ratelimit_state unseeded_warning =
 	RATELIMIT_STATE_INIT("warn_unseeded_randomness", HZ, 3);
 static struct ratelimit_state urandom_warning =
 	RATELIMIT_STATE_INIT("warn_urandom_randomness", HZ, 3);
-
 static int ratelimit_disable __read_mostly;
-
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
 
+/*
+ * Returns whether or not the input pool has been seeded and thus guaranteed
+ * to supply cryptographically secure random numbers. This applies to: the
+ * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
+ * ,u64,int,long} family of functions.
+ *
+ * Returns: true if the input pool has been seeded.
+ *          false if the input pool has not been seeded.
+ */
+bool rng_is_initialized(void)
+{
+	return crng_ready();
+}
+EXPORT_SYMBOL(rng_is_initialized);
+
+/* Used by wait_for_random_bytes(), and considered an entropy collector, below. */
+static void try_to_generate_entropy(void);
+
+/*
+ * Wait for the input pool to be seeded and thus guaranteed to supply
+ * cryptographically secure random numbers. This applies to: the /dev/urandom
+ * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
+ * family of functions. Using any of these functions without first calling
+ * this function forfeits the guarantee of security.
+ *
+ * Returns: 0 if the input pool has been seeded.
+ *          -ERESTARTSYS if the function was interrupted by a signal.
+ */
+int wait_for_random_bytes(void)
+{
+	if (likely(crng_ready()))
+		return 0;
+
+	do {
+		int ret;
+		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
+		if (ret)
+			return ret > 0 ? 0 : ret;
+
+		try_to_generate_entropy();
+	} while (!crng_ready());
+
+	return 0;
+}
+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)
+ *	    -ENOENT if module for callback is not alive
+ */
+int add_random_ready_callback(struct random_ready_callback *rdy)
+{
+	struct module *owner;
+	unsigned long flags;
+	int err = -EALREADY;
+
+	if (crng_ready())
+		return err;
+
+	owner = rdy->owner;
+	if (!try_module_get(owner))
+		return -ENOENT;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	if (crng_ready())
+		goto out;
+
+	owner = NULL;
+
+	list_add(&rdy->list, &random_ready_list);
+	err = 0;
+
+out:
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+
+	module_put(owner);
+
+	return err;
+}
+EXPORT_SYMBOL(add_random_ready_callback);
+
+/*
+ * Delete a previously registered readiness callback function.
+ */
+void del_random_ready_callback(struct random_ready_callback *rdy)
+{
+	unsigned long flags;
+	struct module *owner = NULL;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	if (!list_empty(&rdy->list)) {
+		list_del_init(&rdy->list);
+		owner = rdy->owner;
+	}
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+
+	module_put(owner);
+}
+EXPORT_SYMBOL(del_random_ready_callback);
+
+static void process_random_ready_list(void)
+{
+	unsigned long flags;
+	struct random_ready_callback *rdy, *tmp;
+
+	spin_lock_irqsave(&random_ready_list_lock, flags);
+	list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
+		struct module *owner = rdy->owner;
+
+		list_del_init(&rdy->list);
+		rdy->func(rdy);
+		module_put(owner);
+	}
+	spin_unlock_irqrestore(&random_ready_list_lock, flags);
+}
+
+#define warn_unseeded_randomness(previous) \
+	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
+
+static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous)
+{
+#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
+	const bool print_once = false;
+#else
+	static bool print_once __read_mostly;
+#endif
+
+	if (print_once || crng_ready() ||
+	    (previous && (caller == READ_ONCE(*previous))))
+		return;
+	WRITE_ONCE(*previous, caller);
+#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
+	print_once = true;
+#endif
+	if (__ratelimit(&unseeded_warning))
+		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
+				func_name, caller, crng_init);
+}
+
+
+enum {
+	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
+	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
+};
+
+/*
+ * Static global variables
+ */
+static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
+
+static int crng_init_cnt = 0;
+
 /**********************************************************************
  *
  * OS independent entropy store.   Here are the functions which handle
@@ -322,22 +475,6 @@ static void fast_mix(u32 pool[4])
 	pool[2] = c;  pool[3] = d;
 }
 
-static void process_random_ready_list(void)
-{
-	unsigned long flags;
-	struct random_ready_callback *rdy, *tmp;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	list_for_each_entry_safe(rdy, tmp, &random_ready_list, list) {
-		struct module *owner = rdy->owner;
-
-		list_del_init(&rdy->list);
-		rdy->func(rdy);
-		module_put(owner);
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-}
-
 static void credit_entropy_bits(size_t nbits)
 {
 	unsigned int entropy_count, orig, add;
@@ -387,8 +524,6 @@ static DEFINE_PER_CPU(struct crng, crngs) = {
 	.lock = INIT_LOCAL_LOCK(crngs.lock),
 };
 
-static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
-
 /*
  * crng_fast_load() can be called by code in the interrupt service
  * path.  So we can't afford to dilly-dally. Returns the number of
@@ -909,29 +1044,6 @@ static bool drain_entropy(void *buf, size_t nbytes)
 	return true;
 }
 
-#define warn_unseeded_randomness(previous) \
-	_warn_unseeded_randomness(__func__, (void *)_RET_IP_, (previous))
-
-static void _warn_unseeded_randomness(const char *func_name, void *caller, void **previous)
-{
-#ifdef CONFIG_WARN_ALL_UNSEEDED_RANDOM
-	const bool print_once = false;
-#else
-	static bool print_once __read_mostly;
-#endif
-
-	if (print_once || crng_ready() ||
-	    (previous && (caller == READ_ONCE(*previous))))
-		return;
-	WRITE_ONCE(*previous, caller);
-#ifndef CONFIG_WARN_ALL_UNSEEDED_RANDOM
-	print_once = true;
-#endif
-	if (__ratelimit(&unseeded_warning))
-		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n",
-				func_name, caller, crng_init);
-}
-
 /*
  * This function is the exported kernel interface.  It returns some
  * number of good random numbers, suitable for key generation, seeding
@@ -1032,107 +1144,6 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-/*
- * Wait for the urandom pool to be seeded and thus guaranteed to supply
- * cryptographically secure random numbers. This applies to: the /dev/urandom
- * device, the get_random_bytes function, and the get_random_{u32,u64,int,long}
- * family of functions. Using any of these functions without first calling
- * this function forfeits the guarantee of security.
- *
- * Returns: 0 if the urandom pool has been seeded.
- *          -ERESTARTSYS if the function was interrupted by a signal.
- */
-int wait_for_random_bytes(void)
-{
-	if (likely(crng_ready()))
-		return 0;
-
-	do {
-		int ret;
-		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
-		if (ret)
-			return ret > 0 ? 0 : ret;
-
-		try_to_generate_entropy();
-	} while (!crng_ready());
-
-	return 0;
-}
-EXPORT_SYMBOL(wait_for_random_bytes);
-
-/*
- * Returns whether or not the urandom pool has been seeded and thus guaranteed
- * to supply cryptographically secure random numbers. This applies to: the
- * /dev/urandom device, the get_random_bytes function, and the get_random_{u32,
- * ,u64,int,long} family of functions.
- *
- * Returns: true if the urandom pool has been seeded.
- *          false if the urandom pool has not been seeded.
- */
-bool rng_is_initialized(void)
-{
-	return crng_ready();
-}
-EXPORT_SYMBOL(rng_is_initialized);
-
-/*
- * Add a callback function that will be invoked when the nonblocking
- * pool is initialised.
- *
- * returns: 0 if callback is successfully added
- *	    -EALREADY if pool is already initialised (callback not called)
- *	    -ENOENT if module for callback is not alive
- */
-int add_random_ready_callback(struct random_ready_callback *rdy)
-{
-	struct module *owner;
-	unsigned long flags;
-	int err = -EALREADY;
-
-	if (crng_ready())
-		return err;
-
-	owner = rdy->owner;
-	if (!try_module_get(owner))
-		return -ENOENT;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (crng_ready())
-		goto out;
-
-	owner = NULL;
-
-	list_add(&rdy->list, &random_ready_list);
-	err = 0;
-
-out:
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-
-	module_put(owner);
-
-	return err;
-}
-EXPORT_SYMBOL(add_random_ready_callback);
-
-/*
- * Delete a previously registered readiness callback function.
- */
-void del_random_ready_callback(struct random_ready_callback *rdy)
-{
-	unsigned long flags;
-	struct module *owner = NULL;
-
-	spin_lock_irqsave(&random_ready_list_lock, flags);
-	if (!list_empty(&rdy->list)) {
-		list_del_init(&rdy->list);
-		owner = rdy->owner;
-	}
-	spin_unlock_irqrestore(&random_ready_list_lock, flags);
-
-	module_put(owner);
-}
-EXPORT_SYMBOL(del_random_ready_callback);
-
 /*
  * This function will use the architecture-specific hardware random
  * number generator if it is available. It is not recommended for
-- 
2.35.1

Re: [PATCH v3] random: group initialization wait functions

[Eric Biggers]

On Mon, Feb 21, 2022 at 04:14:05PM +0100, Jason A. Donenfeld wrote:
> This pulls all of the readiness waiting-focused functions into the first
> labeled section.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> v3 removes the duplicate declarations for _get_random_bytes() and fasync.
> 
>  drivers/char/random.c | 333 ++++++++++++++++++++++--------------------
>  1 file changed, 172 insertions(+), 161 deletions(-)
> 

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 05/10] random: group crng functions

[Jason A. Donenfeld]

This pulls all of the crng-focused functions into the second labeled
section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 865 +++++++++++++++++++++---------------------
 1 file changed, 442 insertions(+), 423 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 499ad32e3060..737d70f1ead5 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -380,121 +380,13 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void
 }
 
 
-enum {
-	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
-	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
-};
-
-/*
- * Static global variables
- */
-static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
-static struct fasync_struct *fasync;
-
-static int crng_init_cnt = 0;
-static void _get_random_bytes(void *buf, size_t nbytes);
-
-/**********************************************************************
- *
- * OS independent entropy store.   Here are the functions which handle
- * storing entropy in an entropy pool.
- *
- **********************************************************************/
-
-static struct {
-	struct blake2s_state hash;
-	spinlock_t lock;
-	unsigned int entropy_count;
-} input_pool = {
-	.hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
-		    BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
-		    BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
-	.hash.outlen = BLAKE2S_HASH_SIZE,
-	.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
-};
-
-static void extract_entropy(void *buf, size_t nbytes);
-static bool drain_entropy(void *buf, size_t nbytes);
-
-static void crng_reseed(void);
-
-/*
- * This function adds bytes into the entropy "pool".  It does not
- * update the entropy estimate.  The caller should call
- * credit_entropy_bits if this is appropriate.
- */
-static void _mix_pool_bytes(const void *in, size_t nbytes)
-{
-	blake2s_update(&input_pool.hash, in, nbytes);
-}
-
-static void mix_pool_bytes(const void *in, size_t nbytes)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&input_pool.lock, flags);
-	_mix_pool_bytes(in, nbytes);
-	spin_unlock_irqrestore(&input_pool.lock, flags);
-}
-
-struct fast_pool {
-	unsigned long pool[16 / sizeof(long)];
-	unsigned long last;
-	u16 reg_idx;
-	u8 count;
-};
-
-/*
- * This is a fast mixing routine used by the interrupt randomness
- * collector.  It's hardcoded for an 128 bit pool and assumes that any
- * locks that might be needed are taken by the caller.
- */
-static void fast_mix(u32 pool[4])
-{
-	u32 a = pool[0],	b = pool[1];
-	u32 c = pool[2],	d = pool[3];
-
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
-
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
-
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
-
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
-
-	pool[0] = a;  pool[1] = b;
-	pool[2] = c;  pool[3] = d;
-}
-
-static void credit_entropy_bits(size_t nbits)
-{
-	unsigned int entropy_count, orig, add;
-
-	if (!nbits)
-		return;
-
-	add = min_t(size_t, nbits, POOL_BITS);
-
-	do {
-		orig = READ_ONCE(input_pool.entropy_count);
-		entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
-	} while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
-
-	if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
-		crng_reseed();
-}
-
 /*********************************************************************
  *
- * CRNG using CHACHA20
+ * Fast key erasure RNG, the "crng".
+ *
+ * These functions expand entropy from the entropy extractor into
+ * long streams for external consumption using the "fast key erasure"
+ * RNG described at <https://blog.cr.yp.to/20170723-random.html>.
  *
  *********************************************************************/
 
@@ -523,70 +415,14 @@ static DEFINE_PER_CPU(struct crng, crngs) = {
 	.lock = INIT_LOCAL_LOCK(crngs.lock),
 };
 
-/*
- * crng_fast_load() can be called by code in the interrupt service
- * path.  So we can't afford to dilly-dally. Returns the number of
- * bytes processed from cp.
- */
-static size_t crng_fast_load(const void *cp, size_t len)
-{
-	unsigned long flags;
-	u8 *src = (u8 *)cp;
-	size_t ret = 0;
-
-	if (!spin_trylock_irqsave(&base_crng.lock, flags))
-		return 0;
-	if (crng_init != 0) {
-		spin_unlock_irqrestore(&base_crng.lock, flags);
-		return 0;
-	}
-	while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {
-		base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src;
-		src++; crng_init_cnt++; len--; ret++;
-	}
-	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
-		++base_crng.generation;
-		crng_init = 1;
-	}
-	spin_unlock_irqrestore(&base_crng.lock, flags);
-	if (crng_init == 1)
-		pr_notice("fast init done\n");
-	return ret;
-}
+/* Used by crng_reseed() to extract a new seed from the input pool. */
+static bool drain_entropy(void *buf, size_t nbytes);
 
 /*
- * crng_slow_load() is called by add_device_randomness, which has two
- * attributes.  (1) We can't trust the buffer passed to it is
- * guaranteed to be unpredictable (so it might not have any entropy at
- * all), and (2) it doesn't have the performance constraints of
- * crng_fast_load().
- *
- * So, we simply hash the contents in with the current key. Finally,
- * we do *not* advance crng_init_cnt since buffer we may get may be
- * something like a fixed DMI table (for example), which might very
- * well be unique to the machine, but is otherwise unvarying.
+ * This extracts a new crng key from the input pool, but only if there is a
+ * sufficient amount of entropy available, in order to mitigate bruteforcing
+ * of newly added bits.
  */
-static void crng_slow_load(const void *cp, size_t len)
-{
-	unsigned long flags;
-	struct blake2s_state hash;
-
-	blake2s_init(&hash, sizeof(base_crng.key));
-
-	if (!spin_trylock_irqsave(&base_crng.lock, flags))
-		return;
-	if (crng_init != 0) {
-		spin_unlock_irqrestore(&base_crng.lock, flags);
-		return;
-	}
-
-	blake2s_update(&hash, base_crng.key, sizeof(base_crng.key));
-	blake2s_update(&hash, cp, len);
-	blake2s_final(&hash, base_crng.key);
-
-	spin_unlock_irqrestore(&base_crng.lock, flags);
-}
-
 static void crng_reseed(void)
 {
 	unsigned long flags;
@@ -598,7 +434,8 @@ static void crng_reseed(void)
 	if (!drain_entropy(key, sizeof(key)))
 		return;
 
-	/* We copy the new key into the base_crng, overwriting the old one,
+	/*
+	 * We copy the new key into the base_crng, overwriting the old one,
 	 * and update the generation counter. We avoid hitting ULONG_MAX,
 	 * because the per-cpu crngs are initialized to ULONG_MAX, so this
 	 * forces new CPUs that come online to always initialize.
@@ -635,13 +472,11 @@ static void crng_reseed(void)
 }
 
 /*
- * The general form here is based on a "fast key erasure RNG" from
- * <https://blog.cr.yp.to/20170723-random.html>. It generates a ChaCha
- * block using the provided key, and then immediately overwites that
- * key with half the block. It returns the resultant ChaCha state to the
- * user, along with the second half of the block containing 32 bytes of
- * random data that may be used; random_data_len may not be greater than
- * 32.
+ * This generates a ChaCha block using the provided key, and then
+ * immediately overwites that key with half the block. It returns
+ * the resultant ChaCha state to the user, along with the second
+ * half of the block containing 32 bytes of random data that may
+ * be used; random_data_len may not be greater than 32.
  */
 static void crng_fast_key_erasure(u8 key[CHACHA_KEY_SIZE],
 				  u32 chacha_state[CHACHA_STATE_WORDS],
@@ -674,7 +509,8 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 
 	BUG_ON(random_data_len > 32);
 
-	/* For the fast path, we check whether we're ready, unlocked first, and
+	/*
+	 * For the fast path, we check whether we're ready, unlocked first, and
 	 * then re-check once locked later. In the case where we're really not
 	 * ready, we do fast key erasure with the base_crng directly, because
 	 * this is what crng_{fast,slow}_load mutate during early init.
@@ -692,7 +528,8 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 			return;
 	}
 
-	/* If the base_crng is more than 5 minutes old, we reseed, which
+	/*
+	 * If the base_crng is more than 5 minutes old, we reseed, which
 	 * in turn bumps the generation counter that we check below.
 	 */
 	if (unlikely(time_after(jiffies, READ_ONCE(base_crng.birth) + CRNG_RESEED_INTERVAL)))
@@ -701,7 +538,8 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 	local_lock_irqsave(&crngs.lock, flags);
 	crng = raw_cpu_ptr(&crngs);
 
-	/* If our per-cpu crng is older than the base_crng, then it means
+	/*
+	 * If our per-cpu crng is older than the base_crng, then it means
 	 * somebody reseeded the base_crng. In that case, we do fast key
 	 * erasure on the base_crng, and use its output as the new key
 	 * for our per-cpu crng. This brings us up to date with base_crng.
@@ -714,7 +552,8 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 		spin_unlock(&base_crng.lock);
 	}
 
-	/* Finally, when we've made it this far, our per-cpu crng has an up
+	/*
+	 * Finally, when we've made it this far, our per-cpu crng has an up
 	 * to date key, and we can do fast key erasure with it to produce
 	 * some random data and a ChaCha state for the caller. All other
 	 * branches of this function are "unlikely", so most of the time we
@@ -724,54 +563,433 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 	local_unlock_irqrestore(&crngs.lock, flags);
 }
 
-static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
+/*
+ * This function is for crng_init < 2 only.
+ *
+ * crng_fast_load() can be called by code in the interrupt service
+ * path.  So we can't afford to dilly-dally. Returns the number of
+ * bytes processed from cp.
+ */
+static size_t crng_fast_load(const void *cp, size_t len)
+{
+	static int crng_init_cnt = 0;
+	unsigned long flags;
+	u8 *src = (u8 *)cp;
+	size_t ret = 0;
+
+	if (!spin_trylock_irqsave(&base_crng.lock, flags))
+		return 0;
+	if (crng_init != 0) {
+		spin_unlock_irqrestore(&base_crng.lock, flags);
+		return 0;
+	}
+	while (len > 0 && crng_init_cnt < CRNG_INIT_CNT_THRESH) {
+		base_crng.key[crng_init_cnt % sizeof(base_crng.key)] ^= *src;
+		src++; crng_init_cnt++; len--; ret++;
+	}
+	if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
+		++base_crng.generation;
+		crng_init = 1;
+	}
+	spin_unlock_irqrestore(&base_crng.lock, flags);
+	if (crng_init == 1)
+		pr_notice("fast init done\n");
+	return ret;
+}
+
+/*
+ * This function is for crng_init < 2 only.
+ *
+ * crng_slow_load() is called by add_device_randomness, which has two
+ * attributes.  (1) We can't trust the buffer passed to it is
+ * guaranteed to be unpredictable (so it might not have any entropy at
+ * all), and (2) it doesn't have the performance constraints of
+ * crng_fast_load().
+ *
+ * So, we simply hash the contents in with the current key. Finally,
+ * we do *not* advance crng_init_cnt since buffer we may get may be
+ * something like a fixed DMI table (for example), which might very
+ * well be unique to the machine, but is otherwise unvarying.
+ */
+static void crng_slow_load(const void *cp, size_t len)
+{
+	unsigned long flags;
+	struct blake2s_state hash;
+
+	blake2s_init(&hash, sizeof(base_crng.key));
+
+	if (!spin_trylock_irqsave(&base_crng.lock, flags))
+		return;
+	if (crng_init != 0) {
+		spin_unlock_irqrestore(&base_crng.lock, flags);
+		return;
+	}
+
+	blake2s_update(&hash, base_crng.key, sizeof(base_crng.key));
+	blake2s_update(&hash, cp, len);
+	blake2s_final(&hash, base_crng.key);
+
+	spin_unlock_irqrestore(&base_crng.lock, flags);
+}
+
+static void _get_random_bytes(void *buf, size_t nbytes)
 {
-	bool large_request = (nbytes > 256);
-	ssize_t ret = 0;
-	size_t len;
 	u32 chacha_state[CHACHA_STATE_WORDS];
-	u8 output[CHACHA_BLOCK_SIZE];
+	u8 tmp[CHACHA_BLOCK_SIZE];
+	size_t len;
+
+	if (!nbytes)
+		return;
+
+	len = min_t(size_t, 32, nbytes);
+	crng_make_state(chacha_state, buf, len);
+	nbytes -= len;
+	buf += len;
+
+	while (nbytes) {
+		if (nbytes < CHACHA_BLOCK_SIZE) {
+			chacha20_block(chacha_state, tmp);
+			memcpy(buf, tmp, nbytes);
+			memzero_explicit(tmp, sizeof(tmp));
+			break;
+		}
+
+		len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
+		chacha20_block(chacha_state, buf);
+		if (unlikely(chacha_state[12] == 0))
+			++chacha_state[13];
+		nbytes -= len;
+		buf += len;
+	}
+
+	memzero_explicit(chacha_state, sizeof(chacha_state));
+}
+
+/*
+ * This function is the exported kernel interface.  It returns some
+ * number of good random numbers, suitable for key generation, seeding
+ * TCP sequence numbers, etc.  It does not rely on the hardware random
+ * number generator.  For random bytes direct from the hardware RNG
+ * (when available), use get_random_bytes_arch(). In order to ensure
+ * that the randomness provided by this function is okay, the function
+ * wait_for_random_bytes() should be called and return 0 at least once
+ * at any point prior.
+ */
+void get_random_bytes(void *buf, size_t nbytes)
+{
+	static void *previous;
+
+	warn_unseeded_randomness(&previous);
+	_get_random_bytes(buf, nbytes);
+}
+EXPORT_SYMBOL(get_random_bytes);
+
+static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
+{
+	bool large_request = (nbytes > 256);
+	ssize_t ret = 0;
+	size_t len;
+	u32 chacha_state[CHACHA_STATE_WORDS];
+	u8 output[CHACHA_BLOCK_SIZE];
+
+	if (!nbytes)
+		return 0;
+
+	len = min_t(size_t, 32, nbytes);
+	crng_make_state(chacha_state, output, len);
+
+	if (copy_to_user(buf, output, len))
+		return -EFAULT;
+	nbytes -= len;
+	buf += len;
+	ret += len;
+
+	while (nbytes) {
+		if (large_request && need_resched()) {
+			if (signal_pending(current)) {
+				if (ret == 0)
+					ret = -ERESTARTSYS;
+				break;
+			}
+			schedule();
+		}
+
+		chacha20_block(chacha_state, output);
+		if (unlikely(chacha_state[12] == 0))
+			++chacha_state[13];
+
+		len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
+		if (copy_to_user(buf, output, len)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		nbytes -= len;
+		buf += len;
+		ret += len;
+	}
+
+	memzero_explicit(chacha_state, sizeof(chacha_state));
+	memzero_explicit(output, sizeof(output));
+	return ret;
+}
+
+/*
+ * Batched entropy returns random integers. The quality of the random
+ * number is good as /dev/urandom. In order to ensure that the randomness
+ * provided by this function is okay, the function wait_for_random_bytes()
+ * should be called and return 0 at least once at any point prior.
+ */
+struct batched_entropy {
+	union {
+		/*
+		 * We make this 1.5x a ChaCha block, so that we get the
+		 * remaining 32 bytes from fast key erasure, plus one full
+		 * block from the detached ChaCha state. We can increase
+		 * the size of this later if needed so long as we keep the
+		 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE.
+		 */
+		u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))];
+		u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))];
+	};
+	local_lock_t lock;
+	unsigned long generation;
+	unsigned int position;
+};
+
+
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
+	.lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock)
+};
+
+u64 get_random_u64(void)
+{
+	u64 ret;
+	unsigned long flags;
+	struct batched_entropy *batch;
+	static void *previous;
+	unsigned long next_gen;
+
+	warn_unseeded_randomness(&previous);
+
+	local_lock_irqsave(&batched_entropy_u64.lock, flags);
+	batch = raw_cpu_ptr(&batched_entropy_u64);
+
+	next_gen = READ_ONCE(base_crng.generation);
+	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0 ||
+	    next_gen != batch->generation) {
+		_get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64));
+		batch->position = 0;
+		batch->generation = next_gen;
+	}
+
+	ret = batch->entropy_u64[batch->position];
+	batch->entropy_u64[batch->position] = 0;
+	++batch->position;
+	local_unlock_irqrestore(&batched_entropy_u64.lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(get_random_u64);
+
+static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
+	.lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock)
+};
+
+u32 get_random_u32(void)
+{
+	u32 ret;
+	unsigned long flags;
+	struct batched_entropy *batch;
+	static void *previous;
+	unsigned long next_gen;
+
+	warn_unseeded_randomness(&previous);
+
+	local_lock_irqsave(&batched_entropy_u32.lock, flags);
+	batch = raw_cpu_ptr(&batched_entropy_u32);
+
+	next_gen = READ_ONCE(base_crng.generation);
+	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0 ||
+	    next_gen != batch->generation) {
+		_get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32));
+		batch->position = 0;
+		batch->generation = next_gen;
+	}
+
+	ret = batch->entropy_u32[batch->position];
+	batch->entropy_u32[batch->position] = 0;
+	++batch->position;
+	local_unlock_irqrestore(&batched_entropy_u32.lock, flags);
+	return ret;
+}
+EXPORT_SYMBOL(get_random_u32);
+
+/**
+ * randomize_page - Generate a random, page aligned address
+ * @start:	The smallest acceptable address the caller will take.
+ * @range:	The size of the area, starting at @start, within which the
+ *		random address must fall.
+ *
+ * If @start + @range would overflow, @range is capped.
+ *
+ * NOTE: Historical use of randomize_range, which this replaces, presumed that
+ * @start was already page aligned.  We now align it regardless.
+ *
+ * Return: A page aligned address within [start, start + range).  On error,
+ * @start is returned.
+ */
+unsigned long randomize_page(unsigned long start, unsigned long range)
+{
+	if (!PAGE_ALIGNED(start)) {
+		range -= PAGE_ALIGN(start) - start;
+		start = PAGE_ALIGN(start);
+	}
+
+	if (start > ULONG_MAX - range)
+		range = ULONG_MAX - start;
+
+	range >>= PAGE_SHIFT;
+
+	if (range == 0)
+		return start;
+
+	return start + (get_random_long() % range << PAGE_SHIFT);
+}
+
+/*
+ * This function will use the architecture-specific hardware random
+ * number generator if it is available. It is not recommended for
+ * use. Use get_random_bytes() instead. It returns the number of
+ * bytes filled in.
+ */
+size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)
+{
+	size_t left = nbytes;
+	u8 *p = buf;
+
+	while (left) {
+		unsigned long v;
+		size_t chunk = min_t(size_t, left, sizeof(unsigned long));
+
+		if (!arch_get_random_long(&v))
+			break;
+
+		memcpy(p, &v, chunk);
+		p += chunk;
+		left -= chunk;
+	}
+
+	return nbytes - left;
+}
+EXPORT_SYMBOL(get_random_bytes_arch);
+
+enum {
+	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
+	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
+};
+
+/*
+ * Static global variables
+ */
+static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
+static struct fasync_struct *fasync;
+
+/**********************************************************************
+ *
+ * OS independent entropy store.   Here are the functions which handle
+ * storing entropy in an entropy pool.
+ *
+ **********************************************************************/
+
+static struct {
+	struct blake2s_state hash;
+	spinlock_t lock;
+	unsigned int entropy_count;
+} input_pool = {
+	.hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
+		    BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
+		    BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
+	.hash.outlen = BLAKE2S_HASH_SIZE,
+	.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
+};
+
+static void extract_entropy(void *buf, size_t nbytes);
+static bool drain_entropy(void *buf, size_t nbytes);
+
+static void crng_reseed(void);
+
+/*
+ * This function adds bytes into the entropy "pool".  It does not
+ * update the entropy estimate.  The caller should call
+ * credit_entropy_bits if this is appropriate.
+ */
+static void _mix_pool_bytes(const void *in, size_t nbytes)
+{
+	blake2s_update(&input_pool.hash, in, nbytes);
+}
+
+static void mix_pool_bytes(const void *in, size_t nbytes)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&input_pool.lock, flags);
+	_mix_pool_bytes(in, nbytes);
+	spin_unlock_irqrestore(&input_pool.lock, flags);
+}
+
+struct fast_pool {
+	unsigned long pool[16 / sizeof(long)];
+	unsigned long last;
+	u16 reg_idx;
+	u8 count;
+};
+
+/*
+ * This is a fast mixing routine used by the interrupt randomness
+ * collector.  It's hardcoded for an 128 bit pool and assumes that any
+ * locks that might be needed are taken by the caller.
+ */
+static void fast_mix(u32 pool[4])
+{
+	u32 a = pool[0],	b = pool[1];
+	u32 c = pool[2],	d = pool[3];
+
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
 
-	if (!nbytes)
-		return 0;
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
 
-	len = min_t(size_t, 32, nbytes);
-	crng_make_state(chacha_state, output, len);
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
 
-	if (copy_to_user(buf, output, len))
-		return -EFAULT;
-	nbytes -= len;
-	buf += len;
-	ret += len;
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
 
-	while (nbytes) {
-		if (large_request && need_resched()) {
-			if (signal_pending(current)) {
-				if (ret == 0)
-					ret = -ERESTARTSYS;
-				break;
-			}
-			schedule();
-		}
+	pool[0] = a;  pool[1] = b;
+	pool[2] = c;  pool[3] = d;
+}
 
-		chacha20_block(chacha_state, output);
-		if (unlikely(chacha_state[12] == 0))
-			++chacha_state[13];
+static void credit_entropy_bits(size_t nbits)
+{
+	unsigned int entropy_count, orig, add;
 
-		len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
-		if (copy_to_user(buf, output, len)) {
-			ret = -EFAULT;
-			break;
-		}
+	if (!nbits)
+		return;
 
-		nbytes -= len;
-		buf += len;
-		ret += len;
-	}
+	add = min_t(size_t, nbits, POOL_BITS);
 
-	memzero_explicit(chacha_state, sizeof(chacha_state));
-	memzero_explicit(output, sizeof(output));
-	return ret;
+	do {
+		orig = READ_ONCE(input_pool.entropy_count);
+		entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
+	} while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
+
+	if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
+		crng_reseed();
 }
 
 /*********************************************************************
@@ -1040,58 +1258,6 @@ static bool drain_entropy(void *buf, size_t nbytes)
 	return true;
 }
 
-/*
- * This function is the exported kernel interface.  It returns some
- * number of good random numbers, suitable for key generation, seeding
- * TCP sequence numbers, etc.  It does not rely on the hardware random
- * number generator.  For random bytes direct from the hardware RNG
- * (when available), use get_random_bytes_arch(). In order to ensure
- * that the randomness provided by this function is okay, the function
- * wait_for_random_bytes() should be called and return 0 at least once
- * at any point prior.
- */
-static void _get_random_bytes(void *buf, size_t nbytes)
-{
-	u32 chacha_state[CHACHA_STATE_WORDS];
-	u8 tmp[CHACHA_BLOCK_SIZE];
-	size_t len;
-
-	if (!nbytes)
-		return;
-
-	len = min_t(size_t, 32, nbytes);
-	crng_make_state(chacha_state, buf, len);
-	nbytes -= len;
-	buf += len;
-
-	while (nbytes) {
-		if (nbytes < CHACHA_BLOCK_SIZE) {
-			chacha20_block(chacha_state, tmp);
-			memcpy(buf, tmp, nbytes);
-			memzero_explicit(tmp, sizeof(tmp));
-			break;
-		}
-
-		len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
-		chacha20_block(chacha_state, buf);
-		if (unlikely(chacha_state[12] == 0))
-			++chacha_state[13];
-		nbytes -= len;
-		buf += len;
-	}
-
-	memzero_explicit(chacha_state, sizeof(chacha_state));
-}
-
-void get_random_bytes(void *buf, size_t nbytes)
-{
-	static void *previous;
-
-	warn_unseeded_randomness(&previous);
-	_get_random_bytes(buf, nbytes);
-}
-EXPORT_SYMBOL(get_random_bytes);
-
 /*
  * Each time the timer fires, we expect that we got an unpredictable
  * jump in the cycle counter. Even if the timer is running on another
@@ -1141,33 +1307,6 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-/*
- * This function will use the architecture-specific hardware random
- * number generator if it is available. It is not recommended for
- * use. Use get_random_bytes() instead. It returns the number of
- * bytes filled in.
- */
-size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)
-{
-	size_t left = nbytes;
-	u8 *p = buf;
-
-	while (left) {
-		unsigned long v;
-		size_t chunk = min_t(size_t, left, sizeof(unsigned long));
-
-		if (!arch_get_random_long(&v))
-			break;
-
-		memcpy(p, &v, chunk);
-		p += chunk;
-		left -= chunk;
-	}
-
-	return nbytes - left;
-}
-EXPORT_SYMBOL(get_random_bytes_arch);
-
 static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
 static int __init parse_trust_cpu(char *arg)
 {
@@ -1530,126 +1669,6 @@ static int __init random_sysctls_init(void)
 device_initcall(random_sysctls_init);
 #endif	/* CONFIG_SYSCTL */
 
-struct batched_entropy {
-	union {
-		/* We make this 1.5x a ChaCha block, so that we get the
-		 * remaining 32 bytes from fast key erasure, plus one full
-		 * block from the detached ChaCha state. We can increase
-		 * the size of this later if needed so long as we keep the
-		 * formula of (integer_blocks + 0.5) * CHACHA_BLOCK_SIZE.
-		 */
-		u64 entropy_u64[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u64))];
-		u32 entropy_u32[CHACHA_BLOCK_SIZE * 3 / (2 * sizeof(u32))];
-	};
-	local_lock_t lock;
-	unsigned long generation;
-	unsigned int position;
-};
-
-/*
- * Get a random word for internal kernel use only. The quality of the random
- * number is good as /dev/urandom. In order to ensure that the randomness
- * provided by this function is okay, the function wait_for_random_bytes()
- * should be called and return 0 at least once at any point prior.
- */
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u64) = {
-	.lock = INIT_LOCAL_LOCK(batched_entropy_u64.lock)
-};
-
-u64 get_random_u64(void)
-{
-	u64 ret;
-	unsigned long flags;
-	struct batched_entropy *batch;
-	static void *previous;
-	unsigned long next_gen;
-
-	warn_unseeded_randomness(&previous);
-
-	local_lock_irqsave(&batched_entropy_u64.lock, flags);
-	batch = raw_cpu_ptr(&batched_entropy_u64);
-
-	next_gen = READ_ONCE(base_crng.generation);
-	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0 ||
-	    next_gen != batch->generation) {
-		_get_random_bytes(batch->entropy_u64, sizeof(batch->entropy_u64));
-		batch->position = 0;
-		batch->generation = next_gen;
-	}
-
-	ret = batch->entropy_u64[batch->position];
-	batch->entropy_u64[batch->position] = 0;
-	++batch->position;
-	local_unlock_irqrestore(&batched_entropy_u64.lock, flags);
-	return ret;
-}
-EXPORT_SYMBOL(get_random_u64);
-
-static DEFINE_PER_CPU(struct batched_entropy, batched_entropy_u32) = {
-	.lock = INIT_LOCAL_LOCK(batched_entropy_u32.lock)
-};
-
-u32 get_random_u32(void)
-{
-	u32 ret;
-	unsigned long flags;
-	struct batched_entropy *batch;
-	static void *previous;
-	unsigned long next_gen;
-
-	warn_unseeded_randomness(&previous);
-
-	local_lock_irqsave(&batched_entropy_u32.lock, flags);
-	batch = raw_cpu_ptr(&batched_entropy_u32);
-
-	next_gen = READ_ONCE(base_crng.generation);
-	if (batch->position % ARRAY_SIZE(batch->entropy_u32) == 0 ||
-	    next_gen != batch->generation) {
-		_get_random_bytes(batch->entropy_u32, sizeof(batch->entropy_u32));
-		batch->position = 0;
-		batch->generation = next_gen;
-	}
-
-	ret = batch->entropy_u32[batch->position];
-	batch->entropy_u32[batch->position] = 0;
-	++batch->position;
-	local_unlock_irqrestore(&batched_entropy_u32.lock, flags);
-	return ret;
-}
-EXPORT_SYMBOL(get_random_u32);
-
-/**
- * randomize_page - Generate a random, page aligned address
- * @start:	The smallest acceptable address the caller will take.
- * @range:	The size of the area, starting at @start, within which the
- *		random address must fall.
- *
- * If @start + @range would overflow, @range is capped.
- *
- * NOTE: Historical use of randomize_range, which this replaces, presumed that
- * @start was already page aligned.  We now align it regardless.
- *
- * Return: A page aligned address within [start, start + range).  On error,
- * @start is returned.
- */
-unsigned long randomize_page(unsigned long start, unsigned long range)
-{
-	if (!PAGE_ALIGNED(start)) {
-		range -= PAGE_ALIGN(start) - start;
-		start = PAGE_ALIGN(start);
-	}
-
-	if (start > ULONG_MAX - range)
-		range = ULONG_MAX - start;
-
-	range >>= PAGE_SHIFT;
-
-	if (range == 0)
-		return start;
-
-	return start + (get_random_long() % range << PAGE_SHIFT);
-}
-
 /* Interface for in-kernel drivers of true hardware RNGs.
  * Those devices may produce endless random bits and will be throttled
  * when our pool is full.
-- 
2.35.0

Re: [PATCH v2 05/10] random: group crng functions

[Dominik Brodowski]

> @@ -724,54 +563,433 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
>  	local_unlock_irqrestore(&crngs.lock, flags);
>  }
>  
> -static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
> +/*
> + * This function is for crng_init < 2 only.

No, it's for crng_init == 0 only.

> +/*
> + * This function is for crng_init < 2 only.

Same here.

> + * Batched entropy returns random integers. The quality of the random
> + * number is good as /dev/urandom. In order to ensure that the randomness

/dev/random

> +size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)

Sidenote: We should get rid of the sole caller of that function, and then of
this function. AFAICS, using get_random_bytes() (once rand_initialize() has
been called) should never be less secure than get_random_bytes_arch() IFF
arch_get_random_long() exists -- which is what the sole caller seems to be
interested in.

Otherwise, all looks good. Thanks,

	Dominik

Re: [PATCH v2 05/10] random: group crng functions

[Jason A. Donenfeld]

Hi Dominik,

On Sun, Feb 13, 2022 at 7:57 AM Dominik Brodowski
<linux@dominikbrodowski.net> wrote:
> No, it's for crng_init == 0 only.

Right! Nice catch, thanks.

> > + * Batched entropy returns random integers. The quality of the random
> > + * number is good as /dev/urandom. In order to ensure that the randomness
>
> /dev/random

/dev/urandom is the right analogy, actually, since batched entropy won't wait.

> > +size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)
>
> Sidenote: We should get rid of the sole caller of that function, and then of
> this function. AFAICS, using get_random_bytes() (once rand_initialize() has
> been called) should never be less secure than get_random_bytes_arch() IFF
> arch_get_random_long() exists -- which is what the sole caller seems to be
> interested in.

I agree entirely that we should get rid of this. I think the issue is
vsprintf needs a stable key for siphash that never changes once
initialized, and the earlier they can get something good enough, the
better. If they can't get something good, vsprintf needs to know so it
can defer that to later. So I'm not yet sure the right way to solve
it, but I agree we should find some way to ditch this function.

Jason

Re: [PATCH v2 05/10] random: group crng functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:13PM +0100, Jason A. Donenfeld wrote:
> -	/* We copy the new key into the base_crng, overwriting the old one,
> +	/*
> +	 * We copy the new key into the base_crng, overwriting the old one,
>  	 * and update the generation counter. We avoid hitting ULONG_MAX,
>  	 * because the per-cpu crngs are initialized to ULONG_MAX, so this
>  	 * forces new CPUs that come online to always initialize.
> @@ -635,13 +472,11 @@ static void crng_reseed(void)

Overall looks good, but it's not ideal seeing comments reformatted like this
rather than doing them the right way from the beginning.

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 06/10] random: group entropy extraction functions

[Jason A. Donenfeld]

This pulls all of the entropy extraction-focused functions into the
third labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 217 +++++++++++++++++++++---------------------
 1 file changed, 109 insertions(+), 108 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 737d70f1ead5..8d1ed01c5a9f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -883,23 +883,35 @@ size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes)
 }
 EXPORT_SYMBOL(get_random_bytes_arch);
 
+
+/**********************************************************************
+ *
+ * Entropy accumulation and extraction routines.
+ *
+ * Callers may add entropy via:
+ *
+ *     static void mix_pool_bytes(const void *in, size_t nbytes)
+ *
+ * After which, if added entropy should be credited:
+ *
+ *     static void credit_entropy_bits(size_t nbits)
+ *
+ * Finally, extract entropy via these two, with the latter one
+ * setting the entropy count to zero and extracting only if there
+ * is POOL_MIN_BITS entropy credited prior:
+ *
+ *     static void extract_entropy(void *buf, size_t nbytes)
+ *     static bool drain_entropy(void *buf, size_t nbytes)
+ *
+ **********************************************************************/
+
 enum {
 	POOL_BITS = BLAKE2S_HASH_SIZE * 8,
 	POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
 };
 
-/*
- * Static global variables
- */
+/* For notifying userspace should write into /dev/random. */
 static DECLARE_WAIT_QUEUE_HEAD(random_write_wait);
-static struct fasync_struct *fasync;
-
-/**********************************************************************
- *
- * OS independent entropy store.   Here are the functions which handle
- * storing entropy in an entropy pool.
- *
- **********************************************************************/
 
 static struct {
 	struct blake2s_state hash;
@@ -913,28 +925,106 @@ static struct {
 	.lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
 };
 
-static void extract_entropy(void *buf, size_t nbytes);
-static bool drain_entropy(void *buf, size_t nbytes);
-
-static void crng_reseed(void);
+static void _mix_pool_bytes(const void *in, size_t nbytes)
+{
+	blake2s_update(&input_pool.hash, in, nbytes);
+}
 
 /*
  * This function adds bytes into the entropy "pool".  It does not
  * update the entropy estimate.  The caller should call
  * credit_entropy_bits if this is appropriate.
  */
-static void _mix_pool_bytes(const void *in, size_t nbytes)
+static void mix_pool_bytes(const void *in, size_t nbytes)
 {
-	blake2s_update(&input_pool.hash, in, nbytes);
+	unsigned long flags;
+
+	spin_lock_irqsave(&input_pool.lock, flags);
+	_mix_pool_bytes(in, nbytes);
+	spin_unlock_irqrestore(&input_pool.lock, flags);
 }
 
-static void mix_pool_bytes(const void *in, size_t nbytes)
+static void credit_entropy_bits(size_t nbits)
+{
+	unsigned int entropy_count, orig, add;
+
+	if (!nbits)
+		return;
+
+	add = min_t(size_t, nbits, POOL_BITS);
+
+	do {
+		orig = READ_ONCE(input_pool.entropy_count);
+		entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
+	} while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
+
+	if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
+		crng_reseed();
+}
+
+/*
+ * This is an HKDF-like construction for using the hashed collected entropy
+ * as a PRF key, that's then expanded block-by-block.
+ */
+static void extract_entropy(void *buf, size_t nbytes)
 {
 	unsigned long flags;
+	u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
+	struct {
+		unsigned long rdseed[32 / sizeof(long)];
+		size_t counter;
+	} block;
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
+		if (!arch_get_random_seed_long(&block.rdseed[i]) &&
+		    !arch_get_random_long(&block.rdseed[i]))
+			block.rdseed[i] = random_get_entropy();
+	}
 
 	spin_lock_irqsave(&input_pool.lock, flags);
-	_mix_pool_bytes(in, nbytes);
+
+	/* seed = HASHPRF(last_key, entropy_input) */
+	blake2s_final(&input_pool.hash, seed);
+
+	/* next_key = HASHPRF(seed, RDSEED || 0) */
+	block.counter = 0;
+	blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
+	blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
+
 	spin_unlock_irqrestore(&input_pool.lock, flags);
+	memzero_explicit(next_key, sizeof(next_key));
+
+	while (nbytes) {
+		i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
+		/* output = HASHPRF(seed, RDSEED || ++counter) */
+		++block.counter;
+		blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
+		nbytes -= i;
+		buf += i;
+	}
+
+	memzero_explicit(seed, sizeof(seed));
+	memzero_explicit(&block, sizeof(block));
+}
+
+/*
+ * First we make sure we have POOL_MIN_BITS of entropy in the pool,
+ * and then we drain all of it. Only then can we extract a new key
+ * with extract_entropy().
+ */
+static bool drain_entropy(void *buf, size_t nbytes)
+{
+	unsigned int entropy_count;
+	do {
+		entropy_count = READ_ONCE(input_pool.entropy_count);
+		if (entropy_count < POOL_MIN_BITS)
+			return false;
+	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
+	extract_entropy(buf, nbytes);
+	wake_up_interruptible(&random_write_wait);
+	kill_fasync(&fasync, SIGIO, POLL_OUT);
+	return true;
 }
 
 struct fast_pool {
@@ -974,24 +1064,6 @@ static void fast_mix(u32 pool[4])
 	pool[2] = c;  pool[3] = d;
 }
 
-static void credit_entropy_bits(size_t nbits)
-{
-	unsigned int entropy_count, orig, add;
-
-	if (!nbits)
-		return;
-
-	add = min_t(size_t, nbits, POOL_BITS);
-
-	do {
-		orig = READ_ONCE(input_pool.entropy_count);
-		entropy_count = min_t(unsigned int, POOL_BITS, orig + add);
-	} while (cmpxchg(&input_pool.entropy_count, orig, entropy_count) != orig);
-
-	if (crng_init < 2 && entropy_count >= POOL_MIN_BITS)
-		crng_reseed();
-}
-
 /*********************************************************************
  *
  * Entropy input management
@@ -1187,77 +1259,6 @@ void add_disk_randomness(struct gendisk *disk)
 EXPORT_SYMBOL_GPL(add_disk_randomness);
 #endif
 
-/*********************************************************************
- *
- * Entropy extraction routines
- *
- *********************************************************************/
-
-/*
- * This is an HKDF-like construction for using the hashed collected entropy
- * as a PRF key, that's then expanded block-by-block.
- */
-static void extract_entropy(void *buf, size_t nbytes)
-{
-	unsigned long flags;
-	u8 seed[BLAKE2S_HASH_SIZE], next_key[BLAKE2S_HASH_SIZE];
-	struct {
-		unsigned long rdseed[32 / sizeof(long)];
-		size_t counter;
-	} block;
-	size_t i;
-
-	for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
-		if (!arch_get_random_seed_long(&block.rdseed[i]) &&
-		    !arch_get_random_long(&block.rdseed[i]))
-			block.rdseed[i] = random_get_entropy();
-	}
-
-	spin_lock_irqsave(&input_pool.lock, flags);
-
-	/* seed = HASHPRF(last_key, entropy_input) */
-	blake2s_final(&input_pool.hash, seed);
-
-	/* next_key = HASHPRF(seed, RDSEED || 0) */
-	block.counter = 0;
-	blake2s(next_key, (u8 *)&block, seed, sizeof(next_key), sizeof(block), sizeof(seed));
-	blake2s_init_key(&input_pool.hash, BLAKE2S_HASH_SIZE, next_key, sizeof(next_key));
-
-	spin_unlock_irqrestore(&input_pool.lock, flags);
-	memzero_explicit(next_key, sizeof(next_key));
-
-	while (nbytes) {
-		i = min_t(size_t, nbytes, BLAKE2S_HASH_SIZE);
-		/* output = HASHPRF(seed, RDSEED || ++counter) */
-		++block.counter;
-		blake2s(buf, (u8 *)&block, seed, i, sizeof(block), sizeof(seed));
-		nbytes -= i;
-		buf += i;
-	}
-
-	memzero_explicit(seed, sizeof(seed));
-	memzero_explicit(&block, sizeof(block));
-}
-
-/*
- * First we make sure we have POOL_MIN_BITS of entropy in the pool,
- * and then we drain all of it. Only then can we extract a new key
- * with extract_entropy().
- */
-static bool drain_entropy(void *buf, size_t nbytes)
-{
-	unsigned int entropy_count;
-	do {
-		entropy_count = READ_ONCE(input_pool.entropy_count);
-		if (entropy_count < POOL_MIN_BITS)
-			return false;
-	} while (cmpxchg(&input_pool.entropy_count, entropy_count, 0) != entropy_count);
-	extract_entropy(buf, nbytes);
-	wake_up_interruptible(&random_write_wait);
-	kill_fasync(&fasync, SIGIO, POLL_OUT);
-	return true;
-}
-
 /*
  * Each time the timer fires, we expect that we got an unpredictable
  * jump in the cycle counter. Even if the timer is running on another
-- 
2.35.0

Re: [PATCH v2 06/10] random: group entropy extraction functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:14PM +0100, Jason A. Donenfeld wrote:
> This pulls all of the entropy extraction-focused functions into the
> third labeled section.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 217 +++++++++++++++++++++---------------------
>  1 file changed, 109 insertions(+), 108 deletions(-)
> 

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 07/10] random: group entropy collection functions

[Jason A. Donenfeld]

This pulls all of the entropy collection-focused functions into the
forth labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 367 +++++++++++++++++++++++-------------------
 1 file changed, 205 insertions(+), 162 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 8d1ed01c5a9f..d878c8506af9 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1027,57 +1027,112 @@ static bool drain_entropy(void *buf, size_t nbytes)
 	return true;
 }
 
-struct fast_pool {
-	unsigned long pool[16 / sizeof(long)];
-	unsigned long last;
-	u16 reg_idx;
-	u8 count;
-};
+
+/**********************************************************************
+ *
+ * Entropy collection routines.
+ *
+ * The following exported functions are used for pushing entropy into
+ * the above entropy accumulation routines:
+ *
+ *	void add_device_randomness(const void *buf, size_t size);
+ *	void add_input_randomness(unsigned int type, unsigned int code,
+ *	                          unsigned int value);
+ *	void add_interrupt_randomness(int irq);
+ *	void add_disk_randomness(struct gendisk *disk);
+ *	void add_hwgenerator_randomness(const void *buffer, size_t count,
+ *					size_t entropy);
+ *	void add_bootloader_randomness(const void *buf, size_t size);
+ *
+ * add_device_randomness() adds data to the input pool that
+ * is likely to differ between two devices (or possibly even per boot).
+ * This would be things like MAC addresses or serial numbers, or the
+ * read-out of the RTC. This does *not* credit any actual entropy to
+ * the pool, but it initializes the pool to different values for devices
+ * that might otherwise be identical and have very little entropy
+ * available to them (particularly common in the embedded world).
+ *
+ * add_input_randomness() uses the input layer interrupt timing, as well
+ * as the event type information from the hardware.
+ *
+ * add_disk_randomness() uses what amounts to the seek time of block
+ * layer request events, on a per-disk_devt basis, as input to the
+ * entropy pool. Note that high-speed solid state drives with very low
+ * seek times do not make for good sources of entropy, as their seek
+ * times are usually fairly consistent.
+ *
+ * The above three routines try to estimate how many bits of entropy
+ * to credit. They do this by keeping track of the first and second
+ * order deltas of the event timings.
+ *
+ * add_interrupt_randomness() uses the interrupt timing as random
+ * inputs to the entropy pool. Using the cycle counters and the irq source
+ * as inputs, it feeds the input pool roughly once a second or after 64
+ * interrupts, crediting 1 bit of entropy for whichever comes first.
+ *
+ * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
+ * entropy as specified by the caller. If the entropy pool is full it will
+ * block until more entropy is needed.
+ *
+ * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or
+ * add_device_randomness(), depending on whether or not the configuration
+ * option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
+ *
+ **********************************************************************/
+
+static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
+static int __init parse_trust_cpu(char *arg)
+{
+	return kstrtobool(arg, &trust_cpu);
+}
+early_param("random.trust_cpu", parse_trust_cpu);
 
 /*
- * This is a fast mixing routine used by the interrupt randomness
- * collector.  It's hardcoded for an 128 bit pool and assumes that any
- * locks that might be needed are taken by the caller.
+ * The first collection of entropy occurs at system boot while interrupts
+ * are still turned off. Here we push in RDSEED, a timestamp, and utsname().
+ * Depending on the above configuration knob, RDSEED may be considered
+ * sufficient for initialization. Note that much earlier setup may already
+ * have pushed entropy into the input pool by the time we get here.
  */
-static void fast_mix(u32 pool[4])
+int __init rand_initialize(void)
 {
-	u32 a = pool[0],	b = pool[1];
-	u32 c = pool[2],	d = pool[3];
-
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
+	size_t i;
+	ktime_t now = ktime_get_real();
+	bool arch_init = true;
+	unsigned long rv;
 
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
+	for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) {
+		if (!arch_get_random_seed_long_early(&rv) &&
+		    !arch_get_random_long_early(&rv)) {
+			rv = random_get_entropy();
+			arch_init = false;
+		}
+		mix_pool_bytes(&rv, sizeof(rv));
+	}
+	mix_pool_bytes(&now, sizeof(now));
+	mix_pool_bytes(utsname(), sizeof(*(utsname())));
 
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
+	extract_entropy(base_crng.key, sizeof(base_crng.key));
+	++base_crng.generation;
 
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
+	if (arch_init && trust_cpu && crng_init < 2) {
+		crng_init = 2;
+		pr_notice("crng init done (trusting CPU's manufacturer)\n");
+	}
 
-	pool[0] = a;  pool[1] = b;
-	pool[2] = c;  pool[3] = d;
+	if (ratelimit_disable) {
+		urandom_warning.interval = 0;
+		unseeded_warning.interval = 0;
+	}
+	return 0;
 }
 
-/*********************************************************************
- *
- * Entropy input management
- *
- *********************************************************************/
-
 /* There is one of these per entropy source */
 struct timer_rand_state {
 	cycles_t last_time;
 	long last_delta, last_delta2;
 };
 
-#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
-
 /*
  * Add device- or boot-specific data to the input pool to help
  * initialize it.
@@ -1101,8 +1156,6 @@ void add_device_randomness(const void *buf, size_t size)
 }
 EXPORT_SYMBOL(add_device_randomness);
 
-static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
-
 /*
  * This function adds entropy to the entropy "pool" by using timing
  * delays.  It uses the timer_rand_state structure to make an estimate
@@ -1164,8 +1217,9 @@ void add_input_randomness(unsigned int type, unsigned int code,
 			  unsigned int value)
 {
 	static unsigned char last_value;
+	static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
 
-	/* ignore autorepeat and the like */
+	/* Ignore autorepeat and the like. */
 	if (value == last_value)
 		return;
 
@@ -1175,6 +1229,116 @@ void add_input_randomness(unsigned int type, unsigned int code,
 }
 EXPORT_SYMBOL_GPL(add_input_randomness);
 
+#ifdef CONFIG_BLOCK
+void add_disk_randomness(struct gendisk *disk)
+{
+	if (!disk || !disk->random)
+		return;
+	/* First major is 1, so we get >= 0x200 here. */
+	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
+}
+EXPORT_SYMBOL_GPL(add_disk_randomness);
+
+void rand_initialize_disk(struct gendisk *disk)
+{
+	struct timer_rand_state *state;
+
+	/*
+	 * If kzalloc returns null, we just won't use that entropy
+	 * source.
+	 */
+	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
+	if (state) {
+		state->last_time = INITIAL_JIFFIES;
+		disk->random = state;
+	}
+}
+#endif
+
+/*
+ * Interface for in-kernel drivers of true hardware RNGs.
+ * Those devices may produce endless random bits and will be throttled
+ * when our pool is full.
+ */
+void add_hwgenerator_randomness(const void *buffer, size_t count,
+				size_t entropy)
+{
+	if (unlikely(crng_init == 0)) {
+		size_t ret = crng_fast_load(buffer, count);
+		mix_pool_bytes(buffer, ret);
+		count -= ret;
+		buffer += ret;
+		if (!count || crng_init == 0)
+			return;
+	}
+
+	/*
+	 * Throttle writing if we're above the trickle threshold.
+	 * We'll be woken up again once below POOL_MIN_BITS, when
+	 * the calling thread is about to terminate, or once
+	 * CRNG_RESEED_INTERVAL has elapsed.
+	 */
+	wait_event_interruptible_timeout(random_write_wait,
+			!system_wq || kthread_should_stop() ||
+			input_pool.entropy_count < POOL_MIN_BITS,
+			CRNG_RESEED_INTERVAL);
+	mix_pool_bytes(buffer, count);
+	credit_entropy_bits(entropy);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
+
+/*
+ * Handle random seed passed by bootloader.
+ * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
+ * it would be regarded as device data.
+ * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
+ */
+void add_bootloader_randomness(const void *buf, size_t size)
+{
+	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
+		add_hwgenerator_randomness(buf, size, size * 8);
+	else
+		add_device_randomness(buf, size);
+}
+EXPORT_SYMBOL_GPL(add_bootloader_randomness);
+
+struct fast_pool {
+	unsigned long pool[16 / sizeof(long)];
+	unsigned long last;
+	u16 reg_idx;
+	u8 count;
+};
+
+/*
+ * This is a fast mixing routine used by the interrupt randomness
+ * collector. It's hardcoded for an 128 bit pool and assumes that any
+ * locks that might be needed are taken by the caller.
+ */
+static void fast_mix(u32 pool[4])
+{
+	u32 a = pool[0],	b = pool[1];
+	u32 c = pool[2],	d = pool[3];
+
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
+
+	pool[0] = a;  pool[1] = b;
+	pool[2] = c;  pool[3] = d;
+}
+
 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
 static u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
@@ -1221,7 +1385,8 @@ void add_interrupt_randomness(int irq)
 			fast_pool->count = 0;
 			fast_pool->last = now;
 
-			/* Technically this call means that we're using a spinlock_t
+			/*
+			 * Technically this call means that we're using a spinlock_t
 			 * in the IRQ handler, which isn't terrific for PREEMPT_RT.
 			 * However, this only happens during boot, and then never
 			 * again, so we live with it.
@@ -1243,22 +1408,11 @@ void add_interrupt_randomness(int irq)
 
 	fast_pool->count = 0;
 
-	/* award one bit for the contents of the fast pool */
+	/* Award one bit for the contents of the fast pool. */
 	credit_entropy_bits(1);
 }
 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
 
-#ifdef CONFIG_BLOCK
-void add_disk_randomness(struct gendisk *disk)
-{
-	if (!disk || !disk->random)
-		return;
-	/* first major is 1, so we get >= 0x200 here */
-	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
-}
-EXPORT_SYMBOL_GPL(add_disk_randomness);
-#endif
-
 /*
  * Each time the timer fires, we expect that we got an unpredictable
  * jump in the cycle counter. Even if the timer is running on another
@@ -1308,73 +1462,6 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
-static int __init parse_trust_cpu(char *arg)
-{
-	return kstrtobool(arg, &trust_cpu);
-}
-early_param("random.trust_cpu", parse_trust_cpu);
-
-/*
- * Note that setup_arch() may call add_device_randomness()
- * long before we get here. This allows seeding of the pools
- * with some platform dependent data very early in the boot
- * process. But it limits our options here. We must use
- * statically allocated structures that already have all
- * initializations complete at compile time. We should also
- * take care not to overwrite the precious per platform data
- * we were given.
- */
-int __init rand_initialize(void)
-{
-	size_t i;
-	ktime_t now = ktime_get_real();
-	bool arch_init = true;
-	unsigned long rv;
-
-	for (i = BLAKE2S_BLOCK_SIZE; i > 0; i -= sizeof(rv)) {
-		if (!arch_get_random_seed_long_early(&rv) &&
-		    !arch_get_random_long_early(&rv)) {
-			rv = random_get_entropy();
-			arch_init = false;
-		}
-		mix_pool_bytes(&rv, sizeof(rv));
-	}
-	mix_pool_bytes(&now, sizeof(now));
-	mix_pool_bytes(utsname(), sizeof(*(utsname())));
-
-	extract_entropy(base_crng.key, sizeof(base_crng.key));
-	++base_crng.generation;
-
-	if (arch_init && trust_cpu && crng_init < 2) {
-		crng_init = 2;
-		pr_notice("crng init done (trusting CPU's manufacturer)\n");
-	}
-
-	if (ratelimit_disable) {
-		urandom_warning.interval = 0;
-		unseeded_warning.interval = 0;
-	}
-	return 0;
-}
-
-#ifdef CONFIG_BLOCK
-void rand_initialize_disk(struct gendisk *disk)
-{
-	struct timer_rand_state *state;
-
-	/*
-	 * If kzalloc returns null, we just won't use that entropy
-	 * source.
-	 */
-	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
-	if (state) {
-		state->last_time = INITIAL_JIFFIES;
-		disk->random = state;
-	}
-}
-#endif
-
 static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
 			    loff_t *ppos)
 {
@@ -1669,47 +1756,3 @@ static int __init random_sysctls_init(void)
 }
 device_initcall(random_sysctls_init);
 #endif	/* CONFIG_SYSCTL */
-
-/* Interface for in-kernel drivers of true hardware RNGs.
- * Those devices may produce endless random bits and will be throttled
- * when our pool is full.
- */
-void add_hwgenerator_randomness(const void *buffer, size_t count,
-				size_t entropy)
-{
-	if (unlikely(crng_init == 0)) {
-		size_t ret = crng_fast_load(buffer, count);
-		mix_pool_bytes(buffer, ret);
-		count -= ret;
-		buffer += ret;
-		if (!count || crng_init == 0)
-			return;
-	}
-
-	/* Throttle writing if we're above the trickle threshold.
-	 * We'll be woken up again once below POOL_MIN_BITS, when
-	 * the calling thread is about to terminate, or once
-	 * CRNG_RESEED_INTERVAL has elapsed.
-	 */
-	wait_event_interruptible_timeout(random_write_wait,
-			!system_wq || kthread_should_stop() ||
-			input_pool.entropy_count < POOL_MIN_BITS,
-			CRNG_RESEED_INTERVAL);
-	mix_pool_bytes(buffer, count);
-	credit_entropy_bits(entropy);
-}
-EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
-
-/* Handle random seed passed by bootloader.
- * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
- * it would be regarded as device data.
- * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
- */
-void add_bootloader_randomness(const void *buf, size_t size)
-{
-	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
-		add_hwgenerator_randomness(buf, size, size * 8);
-	else
-		add_device_randomness(buf, size);
-}
-EXPORT_SYMBOL_GPL(add_bootloader_randomness);
-- 
2.35.0

Re: [PATCH v2 07/10] random: group entropy collection functions

[Dominik Brodowski]

> + * add_device_randomness() adds data to the input pool that
> + * is likely to differ between two devices (or possibly even per boot).
> + * This would be things like MAC addresses or serial numbers, or the
> + * read-out of the RTC. This does *not* credit any actual entropy to
> + * the pool, but it initializes the pool to different values for devices
> + * that might otherwise be identical and have very little entropy
> + * available to them (particularly common in the embedded world).
> + *
> + * add_input_randomness() uses the input layer interrupt timing, as well
> + * as the event type information from the hardware.
> + *
> + * add_disk_randomness() uses what amounts to the seek time of block
> + * layer request events, on a per-disk_devt basis, as input to the
> + * entropy pool. Note that high-speed solid state drives with very low
> + * seek times do not make for good sources of entropy, as their seek
> + * times are usually fairly consistent.
> + *
> + * The above three routines try to estimate how many bits of entropy

	*two* (add_device_randomness() does not credit any entropy).

Thanks,
	Dominik

Re: [PATCH v2 07/10] random: group entropy collection functions

[Jason A. Donenfeld]

Nice catch. Fixed.

Jason

Re: [PATCH v2 07/10] random: group entropy collection functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:15PM +0100, Jason A. Donenfeld wrote:
> +/**********************************************************************
> + *
> + * Entropy collection routines.
> + *
> + * The following exported functions are used for pushing entropy into
> + * the above entropy accumulation routines:
> + *
> + *	void add_device_randomness(const void *buf, size_t size);
> + *	void add_input_randomness(unsigned int type, unsigned int code,
> + *	                          unsigned int value);
> + *	void add_interrupt_randomness(int irq);
> + *	void add_disk_randomness(struct gendisk *disk);
> + *	void add_hwgenerator_randomness(const void *buffer, size_t count,
> + *					size_t entropy);
> + *	void add_bootloader_randomness(const void *buf, size_t size);
> + *
> + * add_device_randomness() adds data to the input pool that
> + * is likely to differ between two devices (or possibly even per boot).
> + * This would be things like MAC addresses or serial numbers, or the
> + * read-out of the RTC. This does *not* credit any actual entropy to
> + * the pool, but it initializes the pool to different values for devices
> + * that might otherwise be identical and have very little entropy
> + * available to them (particularly common in the embedded world).

Perhaps this comment should match the order in which these functions are defined
in the file?

- Eric

Re: [PATCH v2 07/10] random: group entropy collection functions

[Jason A. Donenfeld]

On Mon, Feb 21, 2022 at 6:13 AM Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Sat, Feb 12, 2022 at 01:23:15PM +0100, Jason A. Donenfeld wrote:
> > +/**********************************************************************
> > + *
> > + * Entropy collection routines.
> > + *
> > + * The following exported functions are used for pushing entropy into
> > + * the above entropy accumulation routines:
> > + *
> > + *   void add_device_randomness(const void *buf, size_t size);
> > + *   void add_input_randomness(unsigned int type, unsigned int code,
> > + *                             unsigned int value);
> > + *   void add_interrupt_randomness(int irq);
> > + *   void add_disk_randomness(struct gendisk *disk);
> > + *   void add_hwgenerator_randomness(const void *buffer, size_t count,
> > + *                                   size_t entropy);
> > + *   void add_bootloader_randomness(const void *buf, size_t size);
> > + *
> > + * add_device_randomness() adds data to the input pool that
> > + * is likely to differ between two devices (or possibly even per boot).
> > + * This would be things like MAC addresses or serial numbers, or the
> > + * read-out of the RTC. This does *not* credit any actual entropy to
> > + * the pool, but it initializes the pool to different values for devices
> > + * that might otherwise be identical and have very little entropy
> > + * available to them (particularly common in the embedded world).
>
> Perhaps this comment should match the order in which these functions are defined
> in the file?

Sure. Will do

[PATCH v3] random: group entropy collection functions

[Jason A. Donenfeld]

This pulls all of the entropy collection-focused functions into the
forth labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
v3 adjusts the comment to follow the order of functions, per Eric's
request.

 drivers/char/random.c | 370 +++++++++++++++++++++++-------------------
 1 file changed, 206 insertions(+), 164 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index ce530a44b4d0..75e16e2f07e4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1039,60 +1039,112 @@ static bool drain_entropy(void *buf, size_t nbytes)
 	return true;
 }
 
-struct fast_pool {
-	union {
-		u32 pool32[4];
-		u64 pool64[2];
-	};
-	unsigned long last;
-	u16 reg_idx;
-	u8 count;
-};
+
+/**********************************************************************
+ *
+ * Entropy collection routines.
+ *
+ * The following exported functions are used for pushing entropy into
+ * the above entropy accumulation routines:
+ *
+ *	void add_device_randomness(const void *buf, size_t size);
+ *	void add_input_randomness(unsigned int type, unsigned int code,
+ *	                          unsigned int value);
+ *	void add_disk_randomness(struct gendisk *disk);
+ *	void add_hwgenerator_randomness(const void *buffer, size_t count,
+ *					size_t entropy);
+ *	void add_bootloader_randomness(const void *buf, size_t size);
+ *	void add_interrupt_randomness(int irq);
+ *
+ * add_device_randomness() adds data to the input pool that
+ * is likely to differ between two devices (or possibly even per boot).
+ * This would be things like MAC addresses or serial numbers, or the
+ * read-out of the RTC. This does *not* credit any actual entropy to
+ * the pool, but it initializes the pool to different values for devices
+ * that might otherwise be identical and have very little entropy
+ * available to them (particularly common in the embedded world).
+ *
+ * add_input_randomness() uses the input layer interrupt timing, as well
+ * as the event type information from the hardware.
+ *
+ * add_disk_randomness() uses what amounts to the seek time of block
+ * layer request events, on a per-disk_devt basis, as input to the
+ * entropy pool. Note that high-speed solid state drives with very low
+ * seek times do not make for good sources of entropy, as their seek
+ * times are usually fairly consistent.
+ *
+ * The above two routines try to estimate how many bits of entropy
+ * to credit. They do this by keeping track of the first and second
+ * order deltas of the event timings.
+ *
+ * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
+ * entropy as specified by the caller. If the entropy pool is full it will
+ * block until more entropy is needed.
+ *
+ * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or
+ * add_device_randomness(), depending on whether or not the configuration
+ * option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
+ *
+ * add_interrupt_randomness() uses the interrupt timing as random
+ * inputs to the entropy pool. Using the cycle counters and the irq source
+ * as inputs, it feeds the input pool roughly once a second or after 64
+ * interrupts, crediting 1 bit of entropy for whichever comes first.
+ *
+ **********************************************************************/
+
+static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
+static int __init parse_trust_cpu(char *arg)
+{
+	return kstrtobool(arg, &trust_cpu);
+}
+early_param("random.trust_cpu", parse_trust_cpu);
 
 /*
- * This is a fast mixing routine used by the interrupt randomness
- * collector.  It's hardcoded for an 128 bit pool and assumes that any
- * locks that might be needed are taken by the caller.
+ * The first collection of entropy occurs at system boot while interrupts
+ * are still turned off. Here we push in RDSEED, a timestamp, and utsname().
+ * Depending on the above configuration knob, RDSEED may be considered
+ * sufficient for initialization. Note that much earlier setup may already
+ * have pushed entropy into the input pool by the time we get here.
  */
-static void fast_mix(u32 pool[4])
+int __init rand_initialize(void)
 {
-	u32 a = pool[0],	b = pool[1];
-	u32 c = pool[2],	d = pool[3];
-
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
+	size_t i;
+	ktime_t now = ktime_get_real();
+	bool arch_init = true;
+	unsigned long rv;
 
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
+	for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
+		if (!arch_get_random_seed_long_early(&rv) &&
+		    !arch_get_random_long_early(&rv)) {
+			rv = random_get_entropy();
+			arch_init = false;
+		}
+		mix_pool_bytes(&rv, sizeof(rv));
+	}
+	mix_pool_bytes(&now, sizeof(now));
+	mix_pool_bytes(utsname(), sizeof(*(utsname())));
 
-	a += b;			c += d;
-	b = rol32(b, 6);	d = rol32(d, 27);
-	d ^= a;			b ^= c;
+	extract_entropy(base_crng.key, sizeof(base_crng.key));
+	++base_crng.generation;
 
-	a += b;			c += d;
-	b = rol32(b, 16);	d = rol32(d, 14);
-	d ^= a;			b ^= c;
+	if (arch_init && trust_cpu && crng_init < 2) {
+		crng_init = 2;
+		pr_notice("crng init done (trusting CPU's manufacturer)\n");
+	}
 
-	pool[0] = a;  pool[1] = b;
-	pool[2] = c;  pool[3] = d;
+	if (ratelimit_disable) {
+		urandom_warning.interval = 0;
+		unseeded_warning.interval = 0;
+	}
+	return 0;
 }
 
-/*********************************************************************
- *
- * Entropy input management
- *
- *********************************************************************/
-
 /* There is one of these per entropy source */
 struct timer_rand_state {
 	cycles_t last_time;
 	long last_delta, last_delta2;
 };
 
-#define INIT_TIMER_RAND_STATE { INITIAL_JIFFIES, };
-
 /*
  * Add device- or boot-specific data to the input pool to help
  * initialize it.
@@ -1116,8 +1168,6 @@ void add_device_randomness(const void *buf, size_t size)
 }
 EXPORT_SYMBOL(add_device_randomness);
 
-static struct timer_rand_state input_timer_state = INIT_TIMER_RAND_STATE;
-
 /*
  * This function adds entropy to the entropy "pool" by using timing
  * delays.  It uses the timer_rand_state structure to make an estimate
@@ -1179,8 +1229,9 @@ void add_input_randomness(unsigned int type, unsigned int code,
 			  unsigned int value)
 {
 	static unsigned char last_value;
+	static struct timer_rand_state input_timer_state = { INITIAL_JIFFIES };
 
-	/* ignore autorepeat and the like */
+	/* Ignore autorepeat and the like. */
 	if (value == last_value)
 		return;
 
@@ -1190,6 +1241,119 @@ void add_input_randomness(unsigned int type, unsigned int code,
 }
 EXPORT_SYMBOL_GPL(add_input_randomness);
 
+#ifdef CONFIG_BLOCK
+void add_disk_randomness(struct gendisk *disk)
+{
+	if (!disk || !disk->random)
+		return;
+	/* First major is 1, so we get >= 0x200 here. */
+	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
+}
+EXPORT_SYMBOL_GPL(add_disk_randomness);
+
+void rand_initialize_disk(struct gendisk *disk)
+{
+	struct timer_rand_state *state;
+
+	/*
+	 * If kzalloc returns null, we just won't use that entropy
+	 * source.
+	 */
+	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
+	if (state) {
+		state->last_time = INITIAL_JIFFIES;
+		disk->random = state;
+	}
+}
+#endif
+
+/*
+ * Interface for in-kernel drivers of true hardware RNGs.
+ * Those devices may produce endless random bits and will be throttled
+ * when our pool is full.
+ */
+void add_hwgenerator_randomness(const void *buffer, size_t count,
+				size_t entropy)
+{
+	if (unlikely(crng_init == 0)) {
+		size_t ret = crng_fast_load(buffer, count);
+		mix_pool_bytes(buffer, ret);
+		count -= ret;
+		buffer += ret;
+		if (!count || crng_init == 0)
+			return;
+	}
+
+	/*
+	 * Throttle writing if we're above the trickle threshold.
+	 * We'll be woken up again once below POOL_MIN_BITS, when
+	 * the calling thread is about to terminate, or once
+	 * CRNG_RESEED_INTERVAL has elapsed.
+	 */
+	wait_event_interruptible_timeout(random_write_wait,
+			!system_wq || kthread_should_stop() ||
+			input_pool.entropy_count < POOL_MIN_BITS,
+			CRNG_RESEED_INTERVAL);
+	mix_pool_bytes(buffer, count);
+	credit_entropy_bits(entropy);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
+
+/*
+ * Handle random seed passed by bootloader.
+ * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
+ * it would be regarded as device data.
+ * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
+ */
+void add_bootloader_randomness(const void *buf, size_t size)
+{
+	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
+		add_hwgenerator_randomness(buf, size, size * 8);
+	else
+		add_device_randomness(buf, size);
+}
+EXPORT_SYMBOL_GPL(add_bootloader_randomness);
+
+struct fast_pool {
+	union {
+		u32 pool32[4];
+		u64 pool64[2];
+	};
+	unsigned long last;
+	u16 reg_idx;
+	u8 count;
+};
+
+/*
+ * This is a fast mixing routine used by the interrupt randomness
+ * collector. It's hardcoded for an 128 bit pool and assumes that any
+ * locks that might be needed are taken by the caller.
+ */
+static void fast_mix(u32 pool[4])
+{
+	u32 a = pool[0],	b = pool[1];
+	u32 c = pool[2],	d = pool[3];
+
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 6);	d = rol32(d, 27);
+	d ^= a;			b ^= c;
+
+	a += b;			c += d;
+	b = rol32(b, 16);	d = rol32(d, 14);
+	d ^= a;			b ^= c;
+
+	pool[0] = a;  pool[1] = b;
+	pool[2] = c;  pool[3] = d;
+}
+
 static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
 
 static u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
@@ -1259,22 +1423,11 @@ void add_interrupt_randomness(int irq)
 
 	fast_pool->count = 0;
 
-	/* award one bit for the contents of the fast pool */
+	/* Award one bit for the contents of the fast pool. */
 	credit_entropy_bits(1);
 }
 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
 
-#ifdef CONFIG_BLOCK
-void add_disk_randomness(struct gendisk *disk)
-{
-	if (!disk || !disk->random)
-		return;
-	/* first major is 1, so we get >= 0x200 here */
-	add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
-}
-EXPORT_SYMBOL_GPL(add_disk_randomness);
-#endif
-
 /*
  * Each time the timer fires, we expect that we got an unpredictable
  * jump in the cycle counter. Even if the timer is running on another
@@ -1324,73 +1477,6 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
-static int __init parse_trust_cpu(char *arg)
-{
-	return kstrtobool(arg, &trust_cpu);
-}
-early_param("random.trust_cpu", parse_trust_cpu);
-
-/*
- * Note that setup_arch() may call add_device_randomness()
- * long before we get here. This allows seeding of the pools
- * with some platform dependent data very early in the boot
- * process. But it limits our options here. We must use
- * statically allocated structures that already have all
- * initializations complete at compile time. We should also
- * take care not to overwrite the precious per platform data
- * we were given.
- */
-int __init rand_initialize(void)
-{
-	size_t i;
-	ktime_t now = ktime_get_real();
-	bool arch_init = true;
-	unsigned long rv;
-
-	for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
-		if (!arch_get_random_seed_long_early(&rv) &&
-		    !arch_get_random_long_early(&rv)) {
-			rv = random_get_entropy();
-			arch_init = false;
-		}
-		mix_pool_bytes(&rv, sizeof(rv));
-	}
-	mix_pool_bytes(&now, sizeof(now));
-	mix_pool_bytes(utsname(), sizeof(*(utsname())));
-
-	extract_entropy(base_crng.key, sizeof(base_crng.key));
-	++base_crng.generation;
-
-	if (arch_init && trust_cpu && crng_init < 2) {
-		crng_init = 2;
-		pr_notice("crng init done (trusting CPU's manufacturer)\n");
-	}
-
-	if (ratelimit_disable) {
-		urandom_warning.interval = 0;
-		unseeded_warning.interval = 0;
-	}
-	return 0;
-}
-
-#ifdef CONFIG_BLOCK
-void rand_initialize_disk(struct gendisk *disk)
-{
-	struct timer_rand_state *state;
-
-	/*
-	 * If kzalloc returns null, we just won't use that entropy
-	 * source.
-	 */
-	state = kzalloc(sizeof(struct timer_rand_state), GFP_KERNEL);
-	if (state) {
-		state->last_time = INITIAL_JIFFIES;
-		disk->random = state;
-	}
-}
-#endif
-
 static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
 			    loff_t *ppos)
 {
@@ -1685,47 +1771,3 @@ static int __init random_sysctls_init(void)
 }
 device_initcall(random_sysctls_init);
 #endif	/* CONFIG_SYSCTL */
-
-/* Interface for in-kernel drivers of true hardware RNGs.
- * Those devices may produce endless random bits and will be throttled
- * when our pool is full.
- */
-void add_hwgenerator_randomness(const void *buffer, size_t count,
-				size_t entropy)
-{
-	if (unlikely(crng_init == 0)) {
-		size_t ret = crng_fast_load(buffer, count);
-		mix_pool_bytes(buffer, ret);
-		count -= ret;
-		buffer += ret;
-		if (!count || crng_init == 0)
-			return;
-	}
-
-	/* Throttle writing if we're above the trickle threshold.
-	 * We'll be woken up again once below POOL_MIN_BITS, when
-	 * the calling thread is about to terminate, or once
-	 * CRNG_RESEED_INTERVAL has elapsed.
-	 */
-	wait_event_interruptible_timeout(random_write_wait,
-			!system_wq || kthread_should_stop() ||
-			input_pool.entropy_count < POOL_MIN_BITS,
-			CRNG_RESEED_INTERVAL);
-	mix_pool_bytes(buffer, count);
-	credit_entropy_bits(entropy);
-}
-EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
-
-/* Handle random seed passed by bootloader.
- * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise
- * it would be regarded as device data.
- * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.
- */
-void add_bootloader_randomness(const void *buf, size_t size)
-{
-	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
-		add_hwgenerator_randomness(buf, size, size * 8);
-	else
-		add_device_randomness(buf, size);
-}
-EXPORT_SYMBOL_GPL(add_bootloader_randomness);
-- 
2.35.1

Re: [PATCH v3] random: group entropy collection functions

[Eric Biggers]

On Mon, Feb 21, 2022 at 04:18:19PM +0100, Jason A. Donenfeld wrote:
> This pulls all of the entropy collection-focused functions into the
> forth labeled section.

forth => fourth

> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
> v3 adjusts the comment to follow the order of functions, per Eric's
> request.
> 
>  drivers/char/random.c | 370 +++++++++++++++++++++++-------------------
>  1 file changed, 206 insertions(+), 164 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 08/10] random: group userspace read/write functions

[Jason A. Donenfeld]

This pulls all of the userspace read/write-focused functions into the
fifth labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 125 ++++++++++++++++++++++++++----------------
 1 file changed, 77 insertions(+), 48 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d878c8506af9..b2af2dc96d20 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1462,30 +1462,61 @@ static void try_to_generate_entropy(void)
 	mix_pool_bytes(&stack.now, sizeof(stack.now));
 }
 
-static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
-			    loff_t *ppos)
+
+/**********************************************************************
+ *
+ * Userspace reader/writer interfaces.
+ *
+ * getrandom(2) is the primary modern interface into the RNG and should
+ * be used in preference to anything else.
+ *
+ * Reading from /dev/random has the same functionality as calling
+ * getrandom(2) with flags=0. In earlier versions, however, it had
+ * vastly different semantics and should therefore be avoided, to
+ * prevent backwards compatibility issues.
+ *
+ * Reading from /dev/urandom has the same functionality as calling
+ * getrandom(2) with flags=GRND_INSECURE. Because it does not block
+ * waiting for the RNG to be ready, it should not be used.
+ *
+ * Writing to either /dev/random or /dev/urandom adds entropy to
+ * the input pool but does not credit it.
+ *
+ * Polling on /dev/random indicates when the RNG is initialized, on
+ * the read side, and when it wants new entropy, on the write side.
+ *
+ * Both /dev/random and /dev/urandom have the same set of ioctls for
+ * adding entropy, getting the entropy count, zeroing the count, and
+ * reseeding the crng.
+ *
+ **********************************************************************/
+
+SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
+		flags)
 {
-	static int maxwarn = 10;
+	if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
+		return -EINVAL;
 
-	if (!crng_ready() && maxwarn > 0) {
-		maxwarn--;
-		if (__ratelimit(&urandom_warning))
-			pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
-				  current->comm, nbytes);
-	}
+	/*
+	 * Requesting insecure and blocking randomness at the same time makes
+	 * no sense.
+	 */
+	if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
+		return -EINVAL;
 
-	return get_random_bytes_user(buf, nbytes);
-}
+	if (count > INT_MAX)
+		count = INT_MAX;
 
-static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
-			   loff_t *ppos)
-{
-	int ret;
+	if (!(flags & GRND_INSECURE) && !crng_ready()) {
+		int ret;
 
-	ret = wait_for_random_bytes();
-	if (ret != 0)
-		return ret;
-	return get_random_bytes_user(buf, nbytes);
+		if (flags & GRND_NONBLOCK)
+			return -EAGAIN;
+		ret = wait_for_random_bytes();
+		if (unlikely(ret))
+			return ret;
+	}
+	return get_random_bytes_user(buf, count);
 }
 
 static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1537,6 +1568,32 @@ static ssize_t random_write(struct file *file, const char __user *buffer,
 	return (ssize_t)count;
 }
 
+static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
+			    loff_t *ppos)
+{
+	static int maxwarn = 10;
+
+	if (!crng_ready() && maxwarn > 0) {
+		maxwarn--;
+		if (__ratelimit(&urandom_warning))
+			pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
+				  current->comm, nbytes);
+	}
+
+	return get_random_bytes_user(buf, nbytes);
+}
+
+static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
+			   loff_t *ppos)
+{
+	int ret;
+
+	ret = wait_for_random_bytes();
+	if (ret != 0)
+		return ret;
+	return get_random_bytes_user(buf, nbytes);
+}
+
 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 {
 	int size, ent_count;
@@ -1545,7 +1602,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 
 	switch (cmd) {
 	case RNDGETENTCNT:
-		/* inherently racy, no point locking */
+		/* Inherently racy, no point locking. */
 		if (put_user(input_pool.entropy_count, p))
 			return -EFAULT;
 		return 0;
@@ -1621,34 +1678,6 @@ const struct file_operations urandom_fops = {
 	.llseek = noop_llseek,
 };
 
-SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
-		flags)
-{
-	if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
-		return -EINVAL;
-
-	/*
-	 * Requesting insecure and blocking randomness at the same time makes
-	 * no sense.
-	 */
-	if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
-		return -EINVAL;
-
-	if (count > INT_MAX)
-		count = INT_MAX;
-
-	if (!(flags & GRND_INSECURE) && !crng_ready()) {
-		int ret;
-
-		if (flags & GRND_NONBLOCK)
-			return -EAGAIN;
-		ret = wait_for_random_bytes();
-		if (unlikely(ret))
-			return ret;
-	}
-	return get_random_bytes_user(buf, count);
-}
-
 /********************************************************************
  *
  * Sysctl interface
-- 
2.35.0

Re: [PATCH v2 08/10] random: group userspace read/write functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:16PM +0100, Jason A. Donenfeld wrote:
> This pulls all of the userspace read/write-focused functions into the
> fifth labeled section.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 125 ++++++++++++++++++++++++++----------------
>  1 file changed, 77 insertions(+), 48 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

[PATCH v2 09/10] random: group sysctl functions

[Jason A. Donenfeld]

This pulls all of the sysctl-focused functions into the sixth labeled
section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 37 +++++++++++++++++++++++++++++++------
 1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index b2af2dc96d20..a32176a46691 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1678,9 +1678,34 @@ const struct file_operations urandom_fops = {
 	.llseek = noop_llseek,
 };
 
+
 /********************************************************************
  *
- * Sysctl interface
+ * Sysctl interface.
+ *
+ * These are partly unused legacy knobs with dummy values to not break
+ * userspace and partly still useful things. They are usually accessible
+ * in /proc/sys/kernel/random/ and are as follows:
+ *
+ * - boot_id - a UUID representing the current boot.
+ *
+ * - uuid - a random UUID, different each time the file is read.
+ *
+ * - poolsize - the number of bits of entropy that the input pool can
+ *   hold, tied to the POOL_BITS constant.
+ *
+ * - entropy_avail - the number of bits of entropy currently in the
+ *   input pool. Always <= poolsize.
+ *
+ * - write_wakeup_threshold - the amount of entropy in the input pool
+ *   below which write polls to /dev/random will unblock, requesting
+ *   more entropy, tied to the POOL_MIN_BITS constant. It is writable
+ *   to avoid breaking old userspaces, but writing to it does not
+ *   change any behavior of the RNG.
+ *
+ * - urandom_min_reseed_secs - fixed to the meaningless value "60".
+ *   It is writable to avoid breaking old userspaces, but writing
+ *   to it does not change any behavior of the RNG.
  *
  ********************************************************************/
 
@@ -1688,8 +1713,8 @@ const struct file_operations urandom_fops = {
 
 #include <linux/sysctl.h>
 
-static int random_min_urandom_seed = 60;
-static int random_write_wakeup_bits = POOL_MIN_BITS;
+static int sysctl_random_min_urandom_seed = 60;
+static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS;
 static int sysctl_poolsize = POOL_BITS;
 static char sysctl_bootid[16];
 
@@ -1746,14 +1771,14 @@ static struct ctl_table random_table[] = {
 	},
 	{
 		.procname	= "write_wakeup_threshold",
-		.data		= &random_write_wakeup_bits,
+		.data		= &sysctl_random_write_wakeup_bits,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
 	{
 		.procname	= "urandom_min_reseed_secs",
-		.data		= &random_min_urandom_seed,
+		.data		= &sysctl_random_min_urandom_seed,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
@@ -1784,4 +1809,4 @@ static int __init random_sysctls_init(void)
 	return 0;
 }
 device_initcall(random_sysctls_init);
-#endif	/* CONFIG_SYSCTL */
+#endif
-- 
2.35.0

Re: [PATCH v2 09/10] random: group sysctl functions

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:17PM +0100, Jason A. Donenfeld wrote:
> This pulls all of the sysctl-focused functions into the sixth labeled
> section.
> 
> No functional changes.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 37 +++++++++++++++++++++++++++++++------
>  1 file changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index b2af2dc96d20..a32176a46691 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1678,9 +1678,34 @@ const struct file_operations urandom_fops = {
>  	.llseek = noop_llseek,
>  };
>  
> +
>  /********************************************************************
>   *
> - * Sysctl interface
> + * Sysctl interface.
> + *
> + * These are partly unused legacy knobs with dummy values to not break
> + * userspace and partly still useful things. They are usually accessible
> + * in /proc/sys/kernel/random/ and are as follows:
> + *
> + * - boot_id - a UUID representing the current boot.
> + *
> + * - uuid - a random UUID, different each time the file is read.
> + *
> + * - poolsize - the number of bits of entropy that the input pool can
> + *   hold, tied to the POOL_BITS constant.
> + *
> + * - entropy_avail - the number of bits of entropy currently in the
> + *   input pool. Always <= poolsize.
> + *
> + * - write_wakeup_threshold - the amount of entropy in the input pool
> + *   below which write polls to /dev/random will unblock, requesting
> + *   more entropy, tied to the POOL_MIN_BITS constant. It is writable
> + *   to avoid breaking old userspaces, but writing to it does not
> + *   change any behavior of the RNG.
> + *
> + * - urandom_min_reseed_secs - fixed to the meaningless value "60".
> + *   It is writable to avoid breaking old userspaces, but writing
> + *   to it does not change any behavior of the RNG.
>   *

This is a nice explanation, but shouldn't
Documentation/admin-guide/sysctl/kernel.rst be updated instead, and this comment
point to there?

>  device_initcall(random_sysctls_init);
> -#endif	/* CONFIG_SYSCTL */
> +#endif

Nit: I'd prefer leaving the comment for the #endif.

- Eric

Re: [PATCH v2 09/10] random: group sysctl functions

[Jason A. Donenfeld]

On Mon, Feb 21, 2022 at 6:21 AM Eric Biggers <ebiggers@kernel.org> wrote:
> This is a nice explanation, but shouldn't
> Documentation/admin-guide/sysctl/kernel.rst be updated instead, and this comment
> point to there?

I'll update kernel.rst for this and for the other thing in a separate
commit to make merge conflicts less annoying.

Re: [PATCH v2 09/10] random: group sysctl functions

[Jason A. Donenfeld]

On Mon, Feb 21, 2022 at 4:27 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> On Mon, Feb 21, 2022 at 6:21 AM Eric Biggers <ebiggers@kernel.org> wrote:
> > This is a nice explanation, but shouldn't
> > Documentation/admin-guide/sysctl/kernel.rst be updated instead, and this comment
> > point to there?
>
> I'll update kernel.rst for this and for the other thing in a separate
> commit to make merge conflicts less annoying.

Actually, it's not that bad. I'll update kernel.rst in the commits
where the behavior needs updating, but I'm fine with the slightly
different wording there for the most part.

[PATCH v2 10/10] random: rewrite header introductory comment

[Jason A. Donenfeld]

Now that we've re-documented the various sections, we can remove the
outdated text here and replace it with a high-level overview.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 183 +++++-------------------------------------
 1 file changed, 21 insertions(+), 162 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a32176a46691..6ffa779b7ed8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2,168 +2,27 @@
 /*
  * Copyright (C) 2017-2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005
- * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999.  All
- * rights reserved.
- */
-
-/*
- * Exported interfaces ---- output
- * ===============================
- *
- * There are four exported interfaces; two for use within the kernel,
- * and two for use from userspace.
- *
- * Exported interfaces ---- userspace output
- * -----------------------------------------
- *
- * The userspace interfaces are two character devices /dev/random and
- * /dev/urandom.  /dev/random is suitable for use when very high
- * quality randomness is desired (for example, for key generation or
- * one-time pads), as it will only return a maximum of the number of
- * bits of randomness (as estimated by the random number generator)
- * contained in the entropy pool.
- *
- * The /dev/urandom device does not have this limit, and will return
- * as many bytes as are requested.  As more and more random bytes are
- * requested without giving time for the entropy pool to recharge,
- * this will result in random numbers that are merely cryptographically
- * strong.  For many applications, however, this is acceptable.
- *
- * Exported interfaces ---- kernel output
- * --------------------------------------
- *
- * The primary kernel interfaces are:
- *
- *	void get_random_bytes(void *buf, size_t nbytes);
- *	u32 get_random_u32()
- *	u64 get_random_u64()
- *	unsigned int get_random_int()
- *	unsigned long get_random_long()
- *
- * These interfaces will return the requested number of random bytes
- * into the given buffer or as a return value. This is equivalent to a
- * read from /dev/urandom. The get_random_{u32,u64,int,long}() family
- * of functions may be higher performance for one-off random integers,
- * because they do a bit of buffering.
- *
- * prandom_u32()
- * -------------
- *
- * For even weaker applications, see the pseudorandom generator
- * prandom_u32(), prandom_max(), and prandom_bytes().  If the random
- * numbers aren't security-critical at all, these are *far* cheaper.
- * Useful for self-tests, random error simulation, randomized backoffs,
- * and any other application where you trust that nobody is trying to
- * maliciously mess with you by guessing the "random" numbers.
- *
- * Exported interfaces ---- input
- * ==============================
- *
- * The current exported interfaces for gathering environmental noise
- * from the devices are:
- *
- *	void add_device_randomness(const void *buf, size_t size);
- *	void add_input_randomness(unsigned int type, unsigned int code,
- *                                unsigned int value);
- *	void add_interrupt_randomness(int irq);
- *	void add_disk_randomness(struct gendisk *disk);
- *	void add_hwgenerator_randomness(const void *buffer, size_t count,
- *					size_t entropy);
- *	void add_bootloader_randomness(const void *buf, size_t size);
- *
- * add_device_randomness() is for adding data to the random pool that
- * is likely to differ between two devices (or possibly even per boot).
- * This would be things like MAC addresses or serial numbers, or the
- * read-out of the RTC. This does *not* add any actual entropy to the
- * pool, but it initializes the pool to different values for devices
- * that might otherwise be identical and have very little entropy
- * available to them (particularly common in the embedded world).
- *
- * add_input_randomness() uses the input layer interrupt timing, as well as
- * the event type information from the hardware.
- *
- * add_interrupt_randomness() uses the interrupt timing as random
- * inputs to the entropy pool. Using the cycle counters and the irq source
- * as inputs, it feeds the randomness roughly once a second.
- *
- * add_disk_randomness() uses what amounts to the seek time of block
- * layer request events, on a per-disk_devt basis, as input to the
- * entropy pool. Note that high-speed solid state drives with very low
- * seek times do not make for good sources of entropy, as their seek
- * times are usually fairly consistent.
- *
- * All of these routines try to estimate how many bits of randomness a
- * particular randomness source.  They do this by keeping track of the
- * first and second order deltas of the event timings.
- *
- * add_hwgenerator_randomness() is for true hardware RNGs, and will credit
- * entropy as specified by the caller. If the entropy pool is full it will
- * block until more entropy is needed.
- *
- * add_bootloader_randomness() is the same as add_hwgenerator_randomness() or
- * add_device_randomness(), depending on whether or not the configuration
- * option CONFIG_RANDOM_TRUST_BOOTLOADER is set.
- *
- * Ensuring unpredictability at system startup
- * ============================================
- *
- * When any operating system starts up, it will go through a sequence
- * of actions that are fairly predictable by an adversary, especially
- * if the start-up does not involve interaction with a human operator.
- * This reduces the actual number of bits of unpredictability in the
- * entropy pool below the value in entropy_count.  In order to
- * counteract this effect, it helps to carry information in the
- * entropy pool across shut-downs and start-ups.  To do this, put the
- * following lines an appropriate script which is run during the boot
- * sequence:
- *
- *	echo "Initializing random number generator..."
- *	random_seed=/var/run/random-seed
- *	# Carry a random seed from start-up to start-up
- *	# Load and then save the whole entropy pool
- *	if [ -f $random_seed ]; then
- *		cat $random_seed >/dev/urandom
- *	else
- *		touch $random_seed
- *	fi
- *	chmod 600 $random_seed
- *	dd if=/dev/urandom of=$random_seed count=1 bs=512
- *
- * and the following lines in an appropriate script which is run as
- * the system is shutdown:
- *
- *	# Carry a random seed from shut-down to start-up
- *	# Save the whole entropy pool
- *	echo "Saving random seed..."
- *	random_seed=/var/run/random-seed
- *	touch $random_seed
- *	chmod 600 $random_seed
- *	dd if=/dev/urandom of=$random_seed count=1 bs=512
- *
- * For example, on most modern systems using the System V init
- * scripts, such code fragments would be found in
- * /etc/rc.d/init.d/random.  On older Linux systems, the correct script
- * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0.
- *
- * Effectively, these commands cause the contents of the entropy pool
- * to be saved at shut-down time and reloaded into the entropy pool at
- * start-up.  (The 'dd' in the addition to the bootup script is to
- * make sure that /etc/random-seed is different for every start-up,
- * even if the system crashes without executing rc.0.)  Even with
- * complete knowledge of the start-up activities, predicting the state
- * of the entropy pool requires knowledge of the previous history of
- * the system.
- *
- * Configuring the /dev/random driver under Linux
- * ==============================================
- *
- * The /dev/random driver under Linux uses minor numbers 8 and 9 of
- * the /dev/mem major number (#1).  So if your system does not have
- * /dev/random and /dev/urandom created already, they can be created
- * by using the commands:
- *
- *	mknod /dev/random c 1 8
- *	mknod /dev/urandom c 1 9
+ * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All rights reserved.
+ *
+ * This driver produces cryptographically secure pseudorandom data. It is divided
+ * into roughly six sections, each with a section header:
+ *
+ *   - Initialization and readiness waiting.
+ *   - Fast key erasure RNG, the "crng".
+ *   - Entropy accumulation and extraction routines.
+ *   - Entropy collection routines.
+ *   - Userspace reader/writer interfaces.
+ *   - Sysctl interface.
+ *
+ * The high level overview is that there is one input pool, into which
+ * various pieces of data are hashed. Some of that data is then "credited" as
+ * having a certain number of bits of entropy. When enough bits of entropy are
+ * available, the hash is finalized and handed as a key to a stream cipher that
+ * expands it indefinitely for various consumers. This key is periodically
+ * refreshed as the various entropy collectors, described below, add data to the
+ * input pool and credit it. There is currently no Fortuna-like scheduler
+ * involved, which can lead to malicious entropy sources causing a premature
+ * reseed, and the entropy estimates are, at best, conservative guesses.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
-- 
2.35.0

Re: [PATCH v2 10/10] random: rewrite header introductory comment

[Eric Biggers]

On Sat, Feb 12, 2022 at 01:23:18PM +0100, Jason A. Donenfeld wrote:
> Now that we've re-documented the various sections, we can remove the
> outdated text here and replace it with a high-level overview.
> 
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Dominik Brodowski <linux@dominikbrodowski.net>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 183 +++++-------------------------------------
>  1 file changed, 21 insertions(+), 162 deletions(-)

Reviewed-by: Eric Biggers <ebiggers@google.com>

- Eric

Re: [PATCH v2 00/10] random: re-group and re-document functions

[Dominik Brodowski]

Am Sat, Feb 12, 2022 at 01:23:08PM +0100 schrieb Jason A. Donenfeld:
> We previously had massive documentation comments and functions strewn
> all about. This attempts to restore sanity by dividing the code into a
> few sections:
> 
> - Initialization and readiness waiting.
> - Fast key erasure RNG.
> - Entropy accumulation and extraction.
> - Entropy collection.
> - Userspace read/write.
> - Sysctl.
> 
> The result of this ordering and this grouping is only 2 forward
> declarations, indicating that this is probably a sensible grouping.
> Also, some documentation that was just hopelessly out of date been
> removed. We'll later look into re-adding parts of this to the Linux man
> pages project.
> 
> No functional changes.

Hi Jason,

thanks for your massive patchset. While some of it was a bit tedious and
repetetive to review, feel free to add my

	Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>

to patchs 1-3, 6 and 8-10. For patches 4, 5 and 7, I have some comments;
once addressed, feel free to add my reviewed-by tag to those as well.

Thanks,
	Dominik

Re: [PATCH v2 00/10] random: re-group and re-document functions

[Jason A. Donenfeld]

On Sun, Feb 13, 2022 at 7:57 AM Dominik Brodowski
<linux@dominikbrodowski.net> wrote:
>
> thanks for your massive patchset. While some of it was a bit tedious and
> repetetive to review, feel free to add my

Thank you very much for slogging through it and reviewing it! Much appreciated.