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2c956a6077
SipHash is a 64-bit keyed hash function that is actually a cryptographically secure PRF, like HMAC. Except SipHash is super fast, and is meant to be used as a hashtable keyed lookup function, or as a general PRF for short input use cases, such as sequence numbers or RNG chaining. For the first usage: There are a variety of attacks known as "hashtable poisoning" in which an attacker forms some data such that the hash of that data will be the same, and then preceeds to fill up all entries of a hashbucket. This is a realistic and well-known denial-of-service vector. Currently hashtables use jhash, which is fast but not secure, and some kind of rotating key scheme (or none at all, which isn't good). SipHash is meant as a replacement for jhash in these cases. There are a modicum of places in the kernel that are vulnerable to hashtable poisoning attacks, either via userspace vectors or network vectors, and there's not a reliable mechanism inside the kernel at the moment to fix it. The first step toward fixing these issues is actually getting a secure primitive into the kernel for developers to use. Then we can, bit by bit, port things over to it as deemed appropriate. While SipHash is extremely fast for a cryptographically secure function, it is likely a bit slower than the insecure jhash, and so replacements will be evaluated on a case-by-case basis based on whether or not the difference in speed is negligible and whether or not the current jhash usage poses a real security risk. For the second usage: A few places in the kernel are using MD5 or SHA1 for creating secure sequence numbers, syn cookies, port numbers, or fast random numbers. SipHash is a faster and more fitting, and more secure replacement for MD5 in those situations. Replacing MD5 and SHA1 with SipHash for these uses is obvious and straight-forward, and so is submitted along with this patch series. There shouldn't be much of a debate over its efficacy. Dozens of languages are already using this internally for their hash tables and PRFs. Some of the BSDs already use this in their kernels. SipHash is a widely known high-speed solution to a widely known set of problems, and it's time we catch-up. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by: Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: David Laight <David.Laight@aculab.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
233 lines
4.8 KiB
C
233 lines
4.8 KiB
C
/* Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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*
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* This file is provided under a dual BSD/GPLv2 license.
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*
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* SipHash: a fast short-input PRF
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* https://131002.net/siphash/
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*
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* This implementation is specifically for SipHash2-4.
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*/
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#include <linux/siphash.h>
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#include <asm/unaligned.h>
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#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
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#include <linux/dcache.h>
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#include <asm/word-at-a-time.h>
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#endif
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#define SIPROUND \
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do { \
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v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
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v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
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v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
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v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
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} while (0)
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#define PREAMBLE(len) \
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u64 v0 = 0x736f6d6570736575ULL; \
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u64 v1 = 0x646f72616e646f6dULL; \
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u64 v2 = 0x6c7967656e657261ULL; \
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u64 v3 = 0x7465646279746573ULL; \
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u64 b = ((u64)(len)) << 56; \
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v3 ^= key->key[1]; \
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v2 ^= key->key[0]; \
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v1 ^= key->key[1]; \
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v0 ^= key->key[0];
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#define POSTAMBLE \
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v3 ^= b; \
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SIPROUND; \
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SIPROUND; \
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v0 ^= b; \
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v2 ^= 0xff; \
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SIPROUND; \
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SIPROUND; \
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SIPROUND; \
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SIPROUND; \
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return (v0 ^ v1) ^ (v2 ^ v3);
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u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key)
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{
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const u8 *end = data + len - (len % sizeof(u64));
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const u8 left = len & (sizeof(u64) - 1);
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u64 m;
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PREAMBLE(len)
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for (; data != end; data += sizeof(u64)) {
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m = le64_to_cpup(data);
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v3 ^= m;
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SIPROUND;
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SIPROUND;
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v0 ^= m;
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}
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#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
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if (left)
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b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) &
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bytemask_from_count(left)));
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#else
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switch (left) {
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case 7: b |= ((u64)end[6]) << 48;
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case 6: b |= ((u64)end[5]) << 40;
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case 5: b |= ((u64)end[4]) << 32;
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case 4: b |= le32_to_cpup(data); break;
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case 3: b |= ((u64)end[2]) << 16;
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case 2: b |= le16_to_cpup(data); break;
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case 1: b |= end[0];
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}
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#endif
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POSTAMBLE
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}
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EXPORT_SYMBOL(__siphash_aligned);
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#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
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u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t *key)
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{
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const u8 *end = data + len - (len % sizeof(u64));
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const u8 left = len & (sizeof(u64) - 1);
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u64 m;
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PREAMBLE(len)
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for (; data != end; data += sizeof(u64)) {
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m = get_unaligned_le64(data);
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v3 ^= m;
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SIPROUND;
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SIPROUND;
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v0 ^= m;
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}
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#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
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if (left)
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b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) &
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bytemask_from_count(left)));
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#else
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switch (left) {
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case 7: b |= ((u64)end[6]) << 48;
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case 6: b |= ((u64)end[5]) << 40;
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case 5: b |= ((u64)end[4]) << 32;
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case 4: b |= get_unaligned_le32(end); break;
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case 3: b |= ((u64)end[2]) << 16;
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case 2: b |= get_unaligned_le16(end); break;
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case 1: b |= end[0];
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}
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#endif
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POSTAMBLE
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}
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EXPORT_SYMBOL(__siphash_unaligned);
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#endif
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/**
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* siphash_1u64 - compute 64-bit siphash PRF value of a u64
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* @first: first u64
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* @key: the siphash key
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*/
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u64 siphash_1u64(const u64 first, const siphash_key_t *key)
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{
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PREAMBLE(8)
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v3 ^= first;
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SIPROUND;
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SIPROUND;
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v0 ^= first;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_1u64);
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/**
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* siphash_2u64 - compute 64-bit siphash PRF value of 2 u64
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* @first: first u64
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* @second: second u64
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* @key: the siphash key
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*/
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u64 siphash_2u64(const u64 first, const u64 second, const siphash_key_t *key)
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{
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PREAMBLE(16)
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v3 ^= first;
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SIPROUND;
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SIPROUND;
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v0 ^= first;
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v3 ^= second;
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SIPROUND;
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SIPROUND;
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v0 ^= second;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_2u64);
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/**
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* siphash_3u64 - compute 64-bit siphash PRF value of 3 u64
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* @first: first u64
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* @second: second u64
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* @third: third u64
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* @key: the siphash key
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*/
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u64 siphash_3u64(const u64 first, const u64 second, const u64 third,
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const siphash_key_t *key)
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{
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PREAMBLE(24)
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v3 ^= first;
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SIPROUND;
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SIPROUND;
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v0 ^= first;
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v3 ^= second;
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SIPROUND;
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SIPROUND;
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v0 ^= second;
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v3 ^= third;
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SIPROUND;
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SIPROUND;
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v0 ^= third;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_3u64);
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/**
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* siphash_4u64 - compute 64-bit siphash PRF value of 4 u64
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* @first: first u64
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* @second: second u64
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* @third: third u64
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* @forth: forth u64
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* @key: the siphash key
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*/
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u64 siphash_4u64(const u64 first, const u64 second, const u64 third,
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const u64 forth, const siphash_key_t *key)
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{
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PREAMBLE(32)
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v3 ^= first;
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SIPROUND;
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SIPROUND;
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v0 ^= first;
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v3 ^= second;
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SIPROUND;
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SIPROUND;
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v0 ^= second;
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v3 ^= third;
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SIPROUND;
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SIPROUND;
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v0 ^= third;
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v3 ^= forth;
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SIPROUND;
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SIPROUND;
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v0 ^= forth;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_4u64);
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u64 siphash_1u32(const u32 first, const siphash_key_t *key)
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{
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PREAMBLE(4)
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b |= first;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_1u32);
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u64 siphash_3u32(const u32 first, const u32 second, const u32 third,
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const siphash_key_t *key)
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{
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u64 combined = (u64)second << 32 | first;
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PREAMBLE(12)
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v3 ^= combined;
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SIPROUND;
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SIPROUND;
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v0 ^= combined;
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b |= third;
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POSTAMBLE
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}
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EXPORT_SYMBOL(siphash_3u32);
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