From f5b98461cb8167ba362ad9f74c41d126b7becea7 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Fri, 6 Jan 2017 19:32:01 +0100 Subject: random: use chacha20 for get_random_int/long Now that our crng uses chacha20, we can rely on its speedy characteristics for replacing MD5, while simultaneously achieving a higher security guarantee. Before the idea was to use these functions if you wanted random integers that aren't stupidly insecure but aren't necessarily secure either, a vague gray zone, that hopefully was "good enough" for its users. With chacha20, we can strengthen this claim, since either we're using an rdrand-like instruction, or we're using the same crng as /dev/urandom. And it's faster than what was before. We could have chosen to replace this with a SipHash-derived function, which might be slightly faster, but at the cost of having yet another RNG construction in the kernel. By moving to chacha20, we have a single RNG to analyze and verify, and we also already get good performance improvements on all platforms. Implementation-wise, rather than use a generic buffer for both get_random_int/long and memcpy based on the size needs, we use a specific buffer for 32-bit reads and for 64-bit reads. This way, we're guaranteed to always have aligned accesses on all platforms. While slightly more verbose in C, the assembly this generates is a lot simpler than otherwise. Finally, on 32-bit platforms where longs and ints are the same size, we simply alias get_random_int to get_random_long. Signed-off-by: Jason A. Donenfeld Suggested-by: Theodore Ts'o Cc: Theodore Ts'o Cc: Hannes Frederic Sowa Cc: Andy Lutomirski Signed-off-by: Theodore Ts'o --- init/main.c | 1 - 1 file changed, 1 deletion(-) (limited to 'init') diff --git a/init/main.c b/init/main.c index b0c9d6facef9..09beb7fc6e8c 100644 --- a/init/main.c +++ b/init/main.c @@ -879,7 +879,6 @@ static void __init do_basic_setup(void) do_ctors(); usermodehelper_enable(); do_initcalls(); - random_int_secret_init(); } static void __init do_pre_smp_initcalls(void) -- cgit