From: Kees Cook <keescook@xxxxxxxxxxxx>
commit d55535232c3dbde9a523a9d10d68670f5fe5dec3 upstream.
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@xxxxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 5 ++---
include/linux/random.h | 1 +
init/main.c | 21 ++++++++++++++-------
3 files changed, 17 insertions(+), 10 deletions(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1789,7 +1789,7 @@ EXPORT_SYMBOL(get_random_bytes_arch);
* data into the pool to prepare it for use. The pool is not cleared
* as that can only decrease the entropy in the pool.
*/
-static void init_std_data(struct entropy_store *r)
+static void __init init_std_data(struct entropy_store *r)
{
int i;
ktime_t now = ktime_get_real();
@@ -1816,7 +1816,7 @@ static void init_std_data(struct entropy
* take care not to overwrite the precious per platform data
* we were given.
*/
-static int rand_initialize(void)
+int __init rand_initialize(void)
{
init_std_data(&input_pool);
init_std_data(&blocking_pool);
@@ -1828,7 +1828,6 @@ static int rand_initialize(void)
}
return 0;
}
-early_initcall(rand_initialize);
#ifdef CONFIG_BLOCK
void rand_initialize_disk(struct gendisk *disk)
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -36,6 +36,7 @@ extern void add_interrupt_randomness(int
extern void get_random_bytes(void *buf, int nbytes);
extern int wait_for_random_bytes(void);
+extern int __init rand_initialize(void);
extern bool rng_is_initialized(void);
extern int add_random_ready_callback(struct random_ready_callback *rdy);
extern void del_random_ready_callback(struct random_ready_callback *rdy);
--- a/init/main.c
+++ b/init/main.c
@@ -531,13 +531,6 @@ asmlinkage __visible void __init start_k
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();
@@ -614,6 +607,20 @@ asmlinkage __visible void __init start_k
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();
sched_clock_postinit();
printk_safe_init();
