From f62384995e4cb7703e5295779c44135c5311770d Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Mon, 26 Sep 2022 17:43:14 +0200 Subject: random: split initialization into early step and later step The full RNG initialization relies on some timestamps, made possible with initialization functions like time_init() and timekeeping_init(). However, these are only available rather late in initialization. Meanwhile, other things, such as memory allocator functions, make use of the RNG much earlier. So split RNG initialization into two phases. We can provide arch randomness very early on, and then later, after timekeeping and such are available, initialize the rest. This ensures that, for example, slabs are properly randomized if RDRAND is available. Without this, CONFIG_SLAB_FREELIST_RANDOM=y loses a degree of its security, because its random seed is potentially deterministic, since it hasn't yet incorporated RDRAND. It also makes it possible to use a better seed in kfence, which currently relies on only the cycle counter. Another positive consequence is that on systems with RDRAND, running with CONFIG_WARN_ALL_UNSEEDED_RANDOM=y results in no warnings at all. One subtle side effect of this change is that on systems with no RDRAND, RDTSC is now only queried by random_init() once, committing the moment of the function call, instead of multiple times as before. This is intentional, as the multiple RDTSCs in a loop before weren't accomplishing very much, with jitter being better provided by try_to_generate_entropy(). Plus, filling blocks with RDTSC is still being done in extract_entropy(), which is necessarily called before random bytes are served anyway. Cc: Andrew Morton Reviewed-by: Kees Cook Reviewed-by: Dominik Brodowski Signed-off-by: Jason A. Donenfeld --- init/main.c | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-) (limited to 'init') diff --git a/init/main.c b/init/main.c index 1fe7942f5d4a8..0866e5d0d467b 100644 --- a/init/main.c +++ b/init/main.c @@ -976,6 +976,9 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) parse_args("Setting extra init args", extra_init_args, NULL, 0, -1, -1, NULL, set_init_arg); + /* Architectural and non-timekeeping rng init, before allocator init */ + random_init_early(command_line); + /* * These use large bootmem allocations and must precede * kmem_cache_init() @@ -1035,17 +1038,13 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) hrtimers_init(); softirq_init(); timekeeping_init(); - kfence_init(); time_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 random_init() - * - time_init() for making random_get_entropy() work on some platforms - * - random_init() to initialize the RNG from from early entropy sources - */ - random_init(command_line); + /* This must be after timekeeping is initialized */ + random_init(); + + /* These make use of the fully initialized rng */ + kfence_init(); boot_init_stack_canary(); perf_event_init(); -- cgit 1.2.3-korg