From: Kees Cook keescook@chromium.org
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@chromium.org Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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();