latent_entropy: Mark functions with __latent_entropy

The __latent_entropy gcc attribute can be used only on functions and
variables.  If it is on a function then the plugin will instrument it for
gathering control-flow entropy. If the attribute is on a variable then
the plugin will initialize it with random contents.  The variable must
be an integer, an integer array type or a structure with integer fields.

These specific functions have been selected because they are init
functions (to help gather boot-time entropy), are called at unpredictable
times, or they have variable loops, each of which provide some level of
latent entropy.

Signed-off-by: Emese Revfy <re.emese@gmail.com>
[kees: expanded commit message]
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/lib/irq_poll.c b/lib/irq_poll.c
index 836f7db..63be749 100644
--- a/lib/irq_poll.c
+++ b/lib/irq_poll.c
@@ -74,7 +74,7 @@
 }
 EXPORT_SYMBOL(irq_poll_complete);
 
-static void irq_poll_softirq(struct softirq_action *h)
+static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
 {
 	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
 	int rearm = 0, budget = irq_poll_budget;