[PATCH] random: make consistent usage of crng_ready()

[PATCH] random: make consistent usage of crng_ready()

[Jason A. Donenfeld]

Rather than sometimes checking `crng_init < 2`, we should always use the
crng_ready() macro, so that should we change anything later, it's
consistent. Additionally, that macro already has a likely() around it,
which means we don't need to open code our own likely() and unlikely()
annotations.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 69591d599338..e37ae7ef039c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -123,7 +123,7 @@ static void try_to_generate_entropy(void);
  */
 int wait_for_random_bytes(void)
 {
-	if (likely(crng_ready()))
+	if (crng_ready())
 		return 0;
 
 	do {
@@ -289,7 +289,7 @@ static void crng_reseed(bool force)
 		++next_gen;
 	WRITE_ONCE(base_crng.generation, next_gen);
 	WRITE_ONCE(base_crng.birth, jiffies);
-	if (crng_init < 2) {
+	if (!crng_ready()) {
 		crng_init = 2;
 		finalize_init = true;
 	}
@@ -352,7 +352,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 	 * ready, we do fast key erasure with the base_crng directly, because
 	 * this is what crng_pre_init_inject() mutates during early init.
 	 */
-	if (unlikely(!crng_ready())) {
+	if (!crng_ready()) {
 		bool ready;
 
 		spin_lock_irqsave(&base_crng.lock, flags);
@@ -795,7 +795,7 @@ static void credit_entropy_bits(size_t nbits)
 		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)
+	if (!crng_ready() && entropy_count >= POOL_MIN_BITS)
 		crng_reseed(false);
 }
 
-- 
2.35.1

Re: [PATCH] random: make consistent usage of crng_ready()

[Eric Biggers]

On Tue, Mar 08, 2022 at 11:25:17AM -0700, Jason A. Donenfeld wrote:
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 69591d599338..e37ae7ef039c 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -123,7 +123,7 @@ static void try_to_generate_entropy(void);
>   */
>  int wait_for_random_bytes(void)
>  {
> -	if (likely(crng_ready()))
> +	if (crng_ready())
>  		return 0;
>  
>  	do {
...
>  	} while (!crng_ready());

I guess the reason why the above doesn't simply use a 'while' loop is because
someone wanted 'likely()' on the first crng_ready()?  That doesn't actually
apply, since crng_ready() has likely() itself, it should just be a 'while' loop.

- Eric

Re: [PATCH] random: make consistent usage of crng_ready()

[Jason A. Donenfeld]

Hi Eric,

On Sat, Mar 12, 2022 at 1:09 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Tue, Mar 08, 2022 at 11:25:17AM -0700, Jason A. Donenfeld wrote:
> > diff --git a/drivers/char/random.c b/drivers/char/random.c
> > index 69591d599338..e37ae7ef039c 100644
> > --- a/drivers/char/random.c
> > +++ b/drivers/char/random.c
> > @@ -123,7 +123,7 @@ static void try_to_generate_entropy(void);
> >   */
> >  int wait_for_random_bytes(void)
> >  {
> > -     if (likely(crng_ready()))
> > +     if (crng_ready())
> >               return 0;
> >
> >       do {
> ...
> >       } while (!crng_ready());
>
> I guess the reason why the above doesn't simply use a 'while' loop is because
> someone wanted 'likely()' on the first crng_ready()?  That doesn't actually
> apply, since crng_ready() has likely() itself, it should just be a 'while' loop.

Nice catch, thanks.

Jason

[PATCH v2] random: make consistent usage of crng_ready()

[Jason A. Donenfeld]

Rather than sometimes checking `crng_init < 2`, we should always use the
crng_ready() macro, so that should we change anything later, it's
consistent. Additionally, that macro already has a likely() around it,
which means we don't need to open code our own likely() and unlikely()
annotations.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index edb5b06544da..596dc664b5bd 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -123,18 +123,13 @@ static void try_to_generate_entropy(void);
  */
 int wait_for_random_bytes(void)
 {
-	if (likely(crng_ready()))
-		return 0;
-
-	do {
+	while (!crng_ready()) {
 		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);
@@ -289,7 +284,7 @@ static void crng_reseed(bool force)
 		++next_gen;
 	WRITE_ONCE(base_crng.generation, next_gen);
 	WRITE_ONCE(base_crng.birth, jiffies);
-	if (crng_init < 2) {
+	if (!crng_ready()) {
 		crng_init = 2;
 		finalize_init = true;
 	}
@@ -352,7 +347,7 @@ static void crng_make_state(u32 chacha_state[CHACHA_STATE_WORDS],
 	 * ready, we do fast key erasure with the base_crng directly, because
 	 * this is what crng_pre_init_inject() mutates during early init.
 	 */
-	if (unlikely(!crng_ready())) {
+	if (!crng_ready()) {
 		bool ready;
 
 		spin_lock_irqsave(&base_crng.lock, flags);
@@ -795,7 +790,7 @@ static void credit_entropy_bits(size_t nbits)
 		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)
+	if (!crng_ready() && entropy_count >= POOL_MIN_BITS)
 		crng_reseed(false);
 }
 
@@ -957,7 +952,7 @@ int __init rand_initialize(void)
 	extract_entropy(base_crng.key, sizeof(base_crng.key));
 	++base_crng.generation;
 
-	if (arch_init && trust_cpu && crng_init < 2) {
+	if (arch_init && trust_cpu && !crng_ready()) {
 		crng_init = 2;
 		pr_notice("crng init done (trusting CPU's manufacturer)\n");
 	}
@@ -1551,7 +1546,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
 	case RNDRESEEDCRNG:
 		if (!capable(CAP_SYS_ADMIN))
 			return -EPERM;
-		if (crng_init < 2)
+		if (!crng_ready())
 			return -ENODATA;
 		crng_reseed(false);
 		return 0;
-- 
2.35.1