random: Do not ignore early device randomness

Commit Message

Kees Cook June 26, 2017, 11:30 p.m. UTC

The add_device_randomness() function would ignore incoming bytes if the
crng wasn't ready. This additionally makes sure to make an early enough
call to add_latent_entropy() to influence the initial stack canary, which
is especially important on non-x86 systems where it stays the same through
the life of the boot.

Signed-off-by: Kees Cook <[e-mail]>
---
 drivers/char/random.c | 5 +++++
 init/main.c           | 1 +
 2 files changed, 6 insertions(+)

Patch

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 01a260f67437..23cab7a8c1c1 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -987,6 +987,11 @@  void add_device_randomness(const void *buf, unsigned int size)
 	unsigned long time = random_get_entropy() ^ jiffies;
 	unsigned long flags;
 
+	if (!crng_ready()) {
+		crng_fast_load(buf, size);
+		return;
+	}
+
 	trace_add_device_randomness(size, _RET_IP_);
 	spin_lock_irqsave(&input_pool.lock, flags);
 	_mix_pool_bytes(&input_pool, buf, size);
diff --git a/init/main.c b/init/main.c
index f866510472d7..6b2c3ab7d76b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -497,6 +497,7 @@  asmlinkage __visible void __init start_kernel(void)
 	/*
 	 * Set up the initial canary ASAP:
 	 */
+	add_latent_entropy();
 	boot_init_stack_canary();
 
 	cgroup_init_early();