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authorJason A. Donenfeld <Jason@zx2c4.com>2017-01-06 21:32:01 +0300
committerTheodore Ts'o <tytso@mit.edu>2017-01-27 22:25:06 +0300
commitf5b98461cb8167ba362ad9f74c41d126b7becea7 (patch)
treea03acbf2b6426dc27d642bacedd567611896d709 /include/linux/random.h
parent5d0e5ea343a0f70351428476bcf8715e0731f26a (diff)
downloadlinux-f5b98461cb8167ba362ad9f74c41d126b7becea7.tar.xz
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 <Jason@zx2c4.com> Suggested-by: Theodore Ts'o <tytso@mit.edu> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'include/linux/random.h')
-rw-r--r--include/linux/random.h1
1 files changed, 0 insertions, 1 deletions
diff --git a/include/linux/random.h b/include/linux/random.h
index 7bd2403e4fef..16ab429735a7 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -37,7 +37,6 @@ extern void get_random_bytes(void *buf, int nbytes);
extern int add_random_ready_callback(struct random_ready_callback *rdy);
extern void del_random_ready_callback(struct random_ready_callback *rdy);
extern void get_random_bytes_arch(void *buf, int nbytes);
-extern int random_int_secret_init(void);
#ifndef MODULE
extern const struct file_operations random_fops, urandom_fops;