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authorJason A. Donenfeld <Jason@zx2c4.com>2022-09-26 17:43:14 +0200
committerJason A. Donenfeld <Jason@zx2c4.com>2022-09-29 21:36:27 +0200
commitf62384995e4cb7703e5295779c44135c5311770d (patch)
treec0ee8ba6ff507f5f48a9657b10dd052742f08640 /include/linux/random.h
parent748bc4dd9e663f23448d8ad7e58c011a67ea1eca (diff)
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 <akpm@linux-foundation.org> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'include/linux/random.h')
-rw-r--r--include/linux/random.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/random.h b/include/linux/random.h
index 3fec206487f6..a9e6e16f9774 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -72,7 +72,8 @@ static inline unsigned long get_random_canary(void)
return get_random_long() & CANARY_MASK;
}
-int __init random_init(const char *command_line);
+void __init random_init_early(const char *command_line);
+void __init random_init(void);
bool rng_is_initialized(void);
int wait_for_random_bytes(void);