diff mbox series

random: always mix cycle counter in add_latent_entropy()

Message ID 20220601205624.92387-1-Jason@zx2c4.com (mailing list archive)
State Mainlined
Commit e3aaf22fb3dbcbf443a0a9eefd0f6ae7a02f8c51
Headers show
Series random: always mix cycle counter in add_latent_entropy() | expand

Commit Message

Jason A. Donenfeld June 1, 2022, 8:56 p.m. UTC 
add_latent_entropy() is called every time a process forks, in
kernel_clone(). This in turn calls add_device_randomness() using the
latent entropy global state. add_device_randomness() does two things:

   2) Mixes into the input pool the latent entropy argument passed; and
   1) Mixes in a cycle counter, a sort of measurement of when the event
      took place, the high precision bits of which are presumably
      difficult to predict.

(2) is impossible without CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y. But (1) is
always possible. However, currently CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n
disables both (1) and (2), instead of just (2).

This commit causes the CONFIG_GCC_PLUGIN_LATENT_ENTROPY=n case to still
do (1) by passing NULL (len 0) to add_device_randomness() when add_latent_
entropy() is called.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: PaX Team <pageexec@freemail.hu>
Cc: Emese Revfy <re.emese@gmail.com>
Fixes: 38addce8b600 ("gcc-plugins: Add latent_entropy plugin")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 include/linux/random.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/include/linux/random.h b/include/linux/random.h
index fae0c84027fd..5880da3f5b5b 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -19,14 +19,14 @@  void add_input_randomness(unsigned int type, unsigned int code,
 void add_interrupt_randomness(int irq) __latent_entropy;
 void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy);
 
-#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 static inline void add_latent_entropy(void)
 {
+#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
 	add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy));
-}
 #else
-static inline void add_latent_entropy(void) { }
+	add_device_randomness(NULL, 0);
 #endif
+}
 
 #if IS_ENABLED(CONFIG_VMGENID)
 void add_vmfork_randomness(const void *unique_vm_id, size_t len);