[PATCH] random: remove rng_has_arch_random()

[PATCH] random: remove rng_has_arch_random()

[Jason A. Donenfeld]

With arch randomness being used by every distro and enabled in
defconfigs, the distinction between rng_has_arch_random() and
rng_is_initialized() is now rather small. In fact, the places where they
differ are now places where paranoid users and system builders really
don't want arch randomness to be used, in which case we should respect
that choice, or places where arch randomness is known to be broken, in
which case that choice is all the more important. So this commit just
removes the function and its one user.

Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 drivers/char/random.c  | 13 -------------
 include/linux/random.h |  1 -
 lib/vsprintf.c         |  3 +--
 3 files changed, 1 insertion(+), 16 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0b78b9c4acf5..655e327d425e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -725,7 +725,6 @@ static void __cold _credit_init_bits(size_t bits)
  *
  **********************************************************************/
 
-static bool used_arch_random;
 static bool trust_cpu __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
 static bool trust_bootloader __initdata = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
 static int __init parse_trust_cpu(char *arg)
@@ -811,7 +810,6 @@ int __init random_init(const char *command_line)
 		crng_reseed();
 	else if (trust_cpu)
 		_credit_init_bits(arch_bits);
-	used_arch_random = arch_bits >= POOL_READY_BITS;
 
 	WARN_ON(register_pm_notifier(&pm_notifier));
 
@@ -820,17 +818,6 @@ int __init random_init(const char *command_line)
 	return 0;
 }
 
-/*
- * Returns whether arch randomness has been mixed into the initial
- * state of the RNG, regardless of whether or not that randomness
- * was credited. Knowing this is only good for a very limited set
- * of uses, such as early init printk pointer obfuscation.
- */
-bool rng_has_arch_random(void)
-{
-	return used_arch_random;
-}
-
 /*
  * Add device- or boot-specific data to the input pool to help
  * initialize it.
diff --git a/include/linux/random.h b/include/linux/random.h
index 223b4bd584e7..20e389a14e5c 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -74,7 +74,6 @@ static inline unsigned long get_random_canary(void)
 
 int __init random_init(const char *command_line);
 bool rng_is_initialized(void);
-bool rng_has_arch_random(void);
 int wait_for_random_bytes(void);
 
 /* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index fb77f7bfd126..3c1853a9d1c0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -769,8 +769,7 @@ static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
 		static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
 		unsigned long flags;
 
-		if (!system_unbound_wq ||
-		    (!rng_is_initialized() && !rng_has_arch_random()) ||
+		if (!system_unbound_wq || !rng_is_initialized() ||
 		    !spin_trylock_irqsave(&filling, flags))
 			return -EAGAIN;
 
-- 
2.35.1

Re: [PATCH] random: remove rng_has_arch_random()

[Petr Mladek]

On Wed 2022-06-08 10:34:59, Jason A. Donenfeld wrote:
> With arch randomness being used by every distro and enabled in
> defconfigs, the distinction between rng_has_arch_random() and
> rng_is_initialized() is now rather small. In fact, the places where they
> differ are now places where paranoid users and system builders really
> don't want arch randomness to be used, in which case we should respect
> that choice, or places where arch randomness is known to be broken, in
> which case that choice is all the more important. So this commit just
> removes the function and its one user.
> 
> Cc: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

I am not expert on random numbers but it sounds reasonable.
Anyway, the change in vsprintf.c looks good:

Reviewed-by: Petr Mladek <pmladek@suse.com>    # vsprintf.c

Best Regards,
Petr