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 <[email protected]> --- Alternatively, ktime_get_real() could get mixed into the pools after timekeeping_init(), and rand_initialize() could be run MUCH early, like after setup_arch()... --- drivers/char/random.c | 5 ++--- include/linux/random.h | 1 + init/main.c | 21 ++++++++++++++------- 3 files changed, 17 insertions(+), 10 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index c75b6cdf0053..deff1aa4d000 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1784,7 +1784,7 @@ 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(); @@ -1811,7 +1811,7 @@ static void init_std_data(struct entropy_store *r) * 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); @@ -1823,7 +1823,6 @@ static int rand_initialize(void) } return 0; } -early_initcall(rand_initialize); #ifdef CONFIG_BLOCK void rand_initialize_disk(struct gendisk *disk) diff --git a/include/linux/random.h b/include/linux/random.h index 445a0ea4ff49..13aeaf5a4bd4 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -36,6 +36,7 @@ extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy; 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); diff --git a/init/main.c b/init/main.c index 18f8f0140fa0..e2b073bf846f 100644 --- a/init/main.c +++ b/init/main.c @@ -550,13 +550,6 @@ 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(); @@ -641,6 +634,20 @@ 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(); -- 2.17.1 -- Kees Cook Pixel Security
