random: move rand_initialize() earlier

Right now rand_initialize() is run as an early_initcall(), but it only
depends on timekeeping_init() (for mixing ktime_get_real() into the
pools). However, the call to boot_init_stack_canary() for stack canary
initialization runs earlier, which triggers a warning at boot:

random: get_random_bytes called from start_kernel+0x357/0x548 with crng_init=0

Instead, this moves rand_initialize() to after timekeeping_init(), and moves
canary initialization here as well.

Note that this warning may still remain for machines that do not have
UEFI RNG support (which initializes the RNG pools during setup_arch()),
or for x86 machines without RDRAND (or booting without "random.trust=on"
or CONFIG_RANDOM_TRUST_CPU=y).

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 14 insertions, 7 deletions

diff --git a/init/main.c b/init/main.c
index 598e278b46f7..55243bc0a067 100644
--- a/init/main.c
+++ b/init/main.c
@@ -564,13 +564,6 @@ asmlinkage __visible void __init start_kernel(void)
         page_address_init();
         pr_notice("%s", linux_banner);
         setup_arch(&command_line);
-        /*
-         * Set up the the initial canary and entropy after arch
-         * and after adding latent and command line entropy.
-         */
-        add_latent_entropy();
-        add_device_randomness(command_line, strlen(command_line));
-        boot_init_stack_canary();
         mm_init_cpumask(&init_mm);
         setup_command_line(command_line);
         setup_nr_cpu_ids();
@@ -655,6 +648,20 @@ asmlinkage __visible void __init start_kernel(void)
         hrtimers_init();
         softirq_init();
         timekeeping_init();
+
+        /*
+         * For best initial stack canary entropy, prepare it after:
+         * - setup_arch() for any UEFI RNG entropy and boot cmdline access
+         * - timekeeping_init() for ktime entropy used in rand_initialize()
+         * - rand_initialize() to get any arch-specific entropy like RDRAND
+         * - add_latent_entropy() to get any latent entropy
+         * - adding command line entropy
+         */
+        rand_initialize();
+        add_latent_entropy();
+        add_device_randomness(command_line, strlen(command_line));
+        boot_init_stack_canary();
+
         time_init();
         printk_safe_init();
         perf_event_init();