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Subject[PATCH] siphash: add cryptographically secure hashtable function
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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.

SipHash isn't just some new trendy hash function. It's been around for a
while, and there really isn't anything that comes remotely close to
being useful in the way SipHash is. With that said, why do we need this?

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.

Linux developers already seem to be aware that this is an issue, and
various places that use hash tables in, say, a network context, use a
non-cryptographically secure function (usually jhash) and then try to
twiddle with the key on a time basis (or in many cases just do nothing
and hope that nobody notices). While this is an admirable attempt at
solving the problem, it doesn't actually fix it. SipHash fixes it.

(It fixes it in such a sound way that you could even build a stream
cipher out of SipHash that would resist the modern cryptanalysis.)

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.

Dozens of languages are already using this internally for their hash
tables. Some of the BSDs already use this in their kernels. SipHash is
a widely known high-speed solution to a widely known problem, and it's
time we catch-up.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
Cc: Daniel J. Bernstein <djb@cr.yp.to>
---
include/linux/siphash.h | 18 ++++++
lib/Makefile | 3 +-
lib/siphash.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 183 insertions(+), 1 deletion(-)
create mode 100644 include/linux/siphash.h
create mode 100644 lib/siphash.c

diff --git a/include/linux/siphash.h b/include/linux/siphash.h
new file mode 100644
index 000000000000..485c2101cc7d
--- /dev/null
+++ b/include/linux/siphash.h
@@ -0,0 +1,18 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#ifndef _LINUX_SIPHASH_H
+#define _LINUX_SIPHASH_H
+
+#include <linux/types.h>
+
+enum siphash24_lengths {
+ SIPHASH24_KEY_LEN = 16
+};
+
+uint64_t siphash24(const uint8_t *data, size_t len, const uint8_t key[SIPHASH24_KEY_LEN]);
+
+#endif /* _LINUX_SIPHASH_H */
diff --git a/lib/Makefile b/lib/Makefile
index 50144a3aeebd..d224337b0d01 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -22,7 +22,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
flex_proportions.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
- earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
+ earlycpio.o seq_buf.o siphash.o \
+ nmi_backtrace.o nodemask.o win_minmax.o

lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/siphash.c b/lib/siphash.c
new file mode 100644
index 000000000000..022d86f04b9b
--- /dev/null
+++ b/lib/siphash.c
@@ -0,0 +1,163 @@
+/* Copyright (C) 2015-2016 Jason A. Donenfeld <Jason@zx2c4.com>
+ * Copyright (C) 2012-2014 Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
+ * Copyright (C) 2012-2014 Daniel J. Bernstein <djb@cr.yp.to>
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+
+#define ROTL(x,b) (uint64_t)(((x) << (b)) | ((x) >> (64 - (b))))
+#define U8TO64(p) le64_to_cpu(*(__le64 *)(p))
+
+#define SIPROUND \
+ do { \
+ v0 += v1; v1 = ROTL(v1, 13); v1 ^= v0; v0 = ROTL(v0, 32); \
+ v2 += v3; v3 = ROTL(v3, 16); v3 ^= v2; \
+ v0 += v3; v3 = ROTL(v3, 21); v3 ^= v0; \
+ v2 += v1; v1 = ROTL(v1, 17); v1 ^= v2; v2 = ROTL(v2, 32); \
+ } while(0)
+
+__attribute__((optimize("unroll-loops")))
+uint64_t siphash24(const uint8_t *data, size_t len, const uint8_t key[SIPHASH24_KEY_LEN])
+{
+ uint64_t v0 = 0x736f6d6570736575ULL;
+ uint64_t v1 = 0x646f72616e646f6dULL;
+ uint64_t v2 = 0x6c7967656e657261ULL;
+ uint64_t v3 = 0x7465646279746573ULL;
+ uint64_t b;
+ uint64_t k0 = U8TO64(key);
+ uint64_t k1 = U8TO64(key + sizeof(uint64_t));
+ uint64_t m;
+ const uint8_t *end = data + len - (len % sizeof(uint64_t));
+ const uint8_t left = len & (sizeof(uint64_t) - 1);
+ b = ((uint64_t)len) << 56;
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(uint64_t)) {
+ m = U8TO64(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+ switch (left) {
+ case 7: b |= ((uint64_t)data[6]) << 48;
+ case 6: b |= ((uint64_t)data[5]) << 40;
+ case 5: b |= ((uint64_t)data[4]) << 32;
+ case 4: b |= ((uint64_t)data[3]) << 24;
+ case 3: b |= ((uint64_t)data[2]) << 16;
+ case 2: b |= ((uint64_t)data[1]) << 8;
+ case 1: b |= ((uint64_t)data[0]); break;
+ case 0: break;
+ }
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ b = (v0 ^ v1) ^ (v2 ^ v3);
+ return (__force uint64_t)cpu_to_le64(b);
+}
+EXPORT_SYMBOL(siphash24);
+
+#ifdef DEBUG
+static const uint8_t test_vectors[64][8] = {
+ { 0x31, 0x0e, 0x0e, 0xdd, 0x47, 0xdb, 0x6f, 0x72 },
+ { 0xfd, 0x67, 0xdc, 0x93, 0xc5, 0x39, 0xf8, 0x74 },
+ { 0x5a, 0x4f, 0xa9, 0xd9, 0x09, 0x80, 0x6c, 0x0d },
+ { 0x2d, 0x7e, 0xfb, 0xd7, 0x96, 0x66, 0x67, 0x85 },
+ { 0xb7, 0x87, 0x71, 0x27, 0xe0, 0x94, 0x27, 0xcf },
+ { 0x8d, 0xa6, 0x99, 0xcd, 0x64, 0x55, 0x76, 0x18 },
+ { 0xce, 0xe3, 0xfe, 0x58, 0x6e, 0x46, 0xc9, 0xcb },
+ { 0x37, 0xd1, 0x01, 0x8b, 0xf5, 0x00, 0x02, 0xab },
+ { 0x62, 0x24, 0x93, 0x9a, 0x79, 0xf5, 0xf5, 0x93 },
+ { 0xb0, 0xe4, 0xa9, 0x0b, 0xdf, 0x82, 0x00, 0x9e },
+ { 0xf3, 0xb9, 0xdd, 0x94, 0xc5, 0xbb, 0x5d, 0x7a },
+ { 0xa7, 0xad, 0x6b, 0x22, 0x46, 0x2f, 0xb3, 0xf4 },
+ { 0xfb, 0xe5, 0x0e, 0x86, 0xbc, 0x8f, 0x1e, 0x75 },
+ { 0x90, 0x3d, 0x84, 0xc0, 0x27, 0x56, 0xea, 0x14 },
+ { 0xee, 0xf2, 0x7a, 0x8e, 0x90, 0xca, 0x23, 0xf7 },
+ { 0xe5, 0x45, 0xbe, 0x49, 0x61, 0xca, 0x29, 0xa1 },
+ { 0xdb, 0x9b, 0xc2, 0x57, 0x7f, 0xcc, 0x2a, 0x3f },
+ { 0x94, 0x47, 0xbe, 0x2c, 0xf5, 0xe9, 0x9a, 0x69 },
+ { 0x9c, 0xd3, 0x8d, 0x96, 0xf0, 0xb3, 0xc1, 0x4b },
+ { 0xbd, 0x61, 0x79, 0xa7, 0x1d, 0xc9, 0x6d, 0xbb },
+ { 0x98, 0xee, 0xa2, 0x1a, 0xf2, 0x5c, 0xd6, 0xbe },
+ { 0xc7, 0x67, 0x3b, 0x2e, 0xb0, 0xcb, 0xf2, 0xd0 },
+ { 0x88, 0x3e, 0xa3, 0xe3, 0x95, 0x67, 0x53, 0x93 },
+ { 0xc8, 0xce, 0x5c, 0xcd, 0x8c, 0x03, 0x0c, 0xa8 },
+ { 0x94, 0xaf, 0x49, 0xf6, 0xc6, 0x50, 0xad, 0xb8 },
+ { 0xea, 0xb8, 0x85, 0x8a, 0xde, 0x92, 0xe1, 0xbc },
+ { 0xf3, 0x15, 0xbb, 0x5b, 0xb8, 0x35, 0xd8, 0x17 },
+ { 0xad, 0xcf, 0x6b, 0x07, 0x63, 0x61, 0x2e, 0x2f },
+ { 0xa5, 0xc9, 0x1d, 0xa7, 0xac, 0xaa, 0x4d, 0xde },
+ { 0x71, 0x65, 0x95, 0x87, 0x66, 0x50, 0xa2, 0xa6 },
+ { 0x28, 0xef, 0x49, 0x5c, 0x53, 0xa3, 0x87, 0xad },
+ { 0x42, 0xc3, 0x41, 0xd8, 0xfa, 0x92, 0xd8, 0x32 },
+ { 0xce, 0x7c, 0xf2, 0x72, 0x2f, 0x51, 0x27, 0x71 },
+ { 0xe3, 0x78, 0x59, 0xf9, 0x46, 0x23, 0xf3, 0xa7 },
+ { 0x38, 0x12, 0x05, 0xbb, 0x1a, 0xb0, 0xe0, 0x12 },
+ { 0xae, 0x97, 0xa1, 0x0f, 0xd4, 0x34, 0xe0, 0x15 },
+ { 0xb4, 0xa3, 0x15, 0x08, 0xbe, 0xff, 0x4d, 0x31 },
+ { 0x81, 0x39, 0x62, 0x29, 0xf0, 0x90, 0x79, 0x02 },
+ { 0x4d, 0x0c, 0xf4, 0x9e, 0xe5, 0xd4, 0xdc, 0xca },
+ { 0x5c, 0x73, 0x33, 0x6a, 0x76, 0xd8, 0xbf, 0x9a },
+ { 0xd0, 0xa7, 0x04, 0x53, 0x6b, 0xa9, 0x3e, 0x0e },
+ { 0x92, 0x59, 0x58, 0xfc, 0xd6, 0x42, 0x0c, 0xad },
+ { 0xa9, 0x15, 0xc2, 0x9b, 0xc8, 0x06, 0x73, 0x18 },
+ { 0x95, 0x2b, 0x79, 0xf3, 0xbc, 0x0a, 0xa6, 0xd4 },
+ { 0xf2, 0x1d, 0xf2, 0xe4, 0x1d, 0x45, 0x35, 0xf9 },
+ { 0x87, 0x57, 0x75, 0x19, 0x04, 0x8f, 0x53, 0xa9 },
+ { 0x10, 0xa5, 0x6c, 0xf5, 0xdf, 0xcd, 0x9a, 0xdb },
+ { 0xeb, 0x75, 0x09, 0x5c, 0xcd, 0x98, 0x6c, 0xd0 },
+ { 0x51, 0xa9, 0xcb, 0x9e, 0xcb, 0xa3, 0x12, 0xe6 },
+ { 0x96, 0xaf, 0xad, 0xfc, 0x2c, 0xe6, 0x66, 0xc7 },
+ { 0x72, 0xfe, 0x52, 0x97, 0x5a, 0x43, 0x64, 0xee },
+ { 0x5a, 0x16, 0x45, 0xb2, 0x76, 0xd5, 0x92, 0xa1 },
+ { 0xb2, 0x74, 0xcb, 0x8e, 0xbf, 0x87, 0x87, 0x0a },
+ { 0x6f, 0x9b, 0xb4, 0x20, 0x3d, 0xe7, 0xb3, 0x81 },
+ { 0xea, 0xec, 0xb2, 0xa3, 0x0b, 0x22, 0xa8, 0x7f },
+ { 0x99, 0x24, 0xa4, 0x3c, 0xc1, 0x31, 0x57, 0x24 },
+ { 0xbd, 0x83, 0x8d, 0x3a, 0xaf, 0xbf, 0x8d, 0xb7 },
+ { 0x0b, 0x1a, 0x2a, 0x32, 0x65, 0xd5, 0x1a, 0xea },
+ { 0x13, 0x50, 0x79, 0xa3, 0x23, 0x1c, 0xe6, 0x60 },
+ { 0x93, 0x2b, 0x28, 0x46, 0xe4, 0xd7, 0x06, 0x66 },
+ { 0xe1, 0x91, 0x5f, 0x5c, 0xb1, 0xec, 0xa4, 0x6c },
+ { 0xf3, 0x25, 0x96, 0x5c, 0xa1, 0x6d, 0x62, 0x9f },
+ { 0x57, 0x5f, 0xf2, 0x8e, 0x60, 0x38, 0x1b, 0xe5 },
+ { 0x72, 0x45, 0x06, 0xeb, 0x4c, 0x32, 0x8a, 0x95 }
+};
+
+static int siphash24_selftest(void)
+{
+ uint8_t in[64], k[16], i;
+ uint64_t out;
+ int ret = 0;
+
+ for (i = 0; i < 16; ++i)
+ k[i] = i;
+
+ for (i = 0; i < 64; ++i) {
+ in[i] = i;
+ out = siphash24(in, i, k);
+ if (memcmp(&out, test_vectors[i], 8)) {
+ printk(KERN_INFO "siphash24: self-test %u: FAIL\n", i + 1);
+ ret = -1;
+ }
+ }
+ if (!ret)
+ printk(KERN_INFO "siphash24: self-tests: pass\n");
+ return ret;
+}
+__initcall(siphash24_selftest);
+#endif
--
2.11.0
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