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Subject[PATCH 4.14 168/237] siphash: use one source of truth for siphash permutations
Date
From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit e73aaae2fa9024832e1f42e30c787c7baf61d014 upstream.

The SipHash family of permutations is currently used in three places:

- siphash.c itself, used in the ordinary way it was intended.
- random32.c, in a construction from an anonymous contributor.
- random.c, as part of its fast_mix function.

Each one of these places reinvents the wheel with the same C code, same
rotation constants, and same symmetry-breaking constants.

This commit tidies things up a bit by placing macros for the
permutations and constants into siphash.h, where each of the three .c
users can access them. It also leaves a note dissuading more users of
them from emerging.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 30 +++++++-----------------------
include/linux/prandom.h | 23 +++++++----------------
include/linux/siphash.h | 28 ++++++++++++++++++++++++++++
lib/siphash.c | 32 ++++++++++----------------------
4 files changed, 52 insertions(+), 61 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -51,6 +51,7 @@
#include <linux/completion.h>
#include <linux/uuid.h>
#include <linux/uaccess.h>
+#include <linux/siphash.h>
#include <crypto/chacha20.h>
#include <crypto/blake2s.h>
#include <asm/processor.h>
@@ -1011,12 +1012,11 @@ struct fast_pool {

static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
#ifdef CONFIG_64BIT
- /* SipHash constants */
- .pool = { 0x736f6d6570736575UL, 0x646f72616e646f6dUL,
- 0x6c7967656e657261UL, 0x7465646279746573UL }
+#define FASTMIX_PERM SIPHASH_PERMUTATION
+ .pool = { SIPHASH_CONST_0, SIPHASH_CONST_1, SIPHASH_CONST_2, SIPHASH_CONST_3 }
#else
- /* HalfSipHash constants */
- .pool = { 0, 0, 0x6c796765U, 0x74656462U }
+#define FASTMIX_PERM HSIPHASH_PERMUTATION
+ .pool = { HSIPHASH_CONST_0, HSIPHASH_CONST_1, HSIPHASH_CONST_2, HSIPHASH_CONST_3 }
#endif
};

@@ -1028,27 +1028,11 @@ static DEFINE_PER_CPU(struct fast_pool,
*/
static void fast_mix(unsigned long s[4], unsigned long v1, unsigned long v2)
{
-#ifdef CONFIG_64BIT
-#define PERM() do { \
- s[0] += s[1]; s[1] = rol64(s[1], 13); s[1] ^= s[0]; s[0] = rol64(s[0], 32); \
- s[2] += s[3]; s[3] = rol64(s[3], 16); s[3] ^= s[2]; \
- s[0] += s[3]; s[3] = rol64(s[3], 21); s[3] ^= s[0]; \
- s[2] += s[1]; s[1] = rol64(s[1], 17); s[1] ^= s[2]; s[2] = rol64(s[2], 32); \
-} while (0)
-#else
-#define PERM() do { \
- s[0] += s[1]; s[1] = rol32(s[1], 5); s[1] ^= s[0]; s[0] = rol32(s[0], 16); \
- s[2] += s[3]; s[3] = rol32(s[3], 8); s[3] ^= s[2]; \
- s[0] += s[3]; s[3] = rol32(s[3], 7); s[3] ^= s[0]; \
- s[2] += s[1]; s[1] = rol32(s[1], 13); s[1] ^= s[2]; s[2] = rol32(s[2], 16); \
-} while (0)
-#endif
-
s[3] ^= v1;
- PERM();
+ FASTMIX_PERM(s[0], s[1], s[2], s[3]);
s[0] ^= v1;
s[3] ^= v2;
- PERM();
+ FASTMIX_PERM(s[0], s[1], s[2], s[3]);
s[0] ^= v2;
}

--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -10,6 +10,7 @@

#include <linux/types.h>
#include <linux/percpu.h>
+#include <linux/siphash.h>

u32 prandom_u32(void);
void prandom_bytes(void *buf, size_t nbytes);
@@ -21,15 +22,10 @@ void prandom_reseed_late(void);
* The core SipHash round function. Each line can be executed in
* parallel given enough CPU resources.
*/
-#define PRND_SIPROUND(v0, v1, v2, v3) ( \
- v0 += v1, v1 = rol64(v1, 13), v2 += v3, v3 = rol64(v3, 16), \
- v1 ^= v0, v0 = rol64(v0, 32), v3 ^= v2, \
- v0 += v3, v3 = rol64(v3, 21), v2 += v1, v1 = rol64(v1, 17), \
- v3 ^= v0, v1 ^= v2, v2 = rol64(v2, 32) \
-)
+#define PRND_SIPROUND(v0, v1, v2, v3) SIPHASH_PERMUTATION(v0, v1, v2, v3)

-#define PRND_K0 (0x736f6d6570736575 ^ 0x6c7967656e657261)
-#define PRND_K1 (0x646f72616e646f6d ^ 0x7465646279746573)
+#define PRND_K0 (SIPHASH_CONST_0 ^ SIPHASH_CONST_2)
+#define PRND_K1 (SIPHASH_CONST_1 ^ SIPHASH_CONST_3)

#elif BITS_PER_LONG == 32
/*
@@ -37,14 +33,9 @@ void prandom_reseed_late(void);
* This is weaker, but 32-bit machines are not used for high-traffic
* applications, so there is less output for an attacker to analyze.
*/
-#define PRND_SIPROUND(v0, v1, v2, v3) ( \
- v0 += v1, v1 = rol32(v1, 5), v2 += v3, v3 = rol32(v3, 8), \
- v1 ^= v0, v0 = rol32(v0, 16), v3 ^= v2, \
- v0 += v3, v3 = rol32(v3, 7), v2 += v1, v1 = rol32(v1, 13), \
- v3 ^= v0, v1 ^= v2, v2 = rol32(v2, 16) \
-)
-#define PRND_K0 0x6c796765
-#define PRND_K1 0x74656462
+#define PRND_SIPROUND(v0, v1, v2, v3) HSIPHASH_PERMUTATION(v0, v1, v2, v3)
+#define PRND_K0 (HSIPHASH_CONST_0 ^ HSIPHASH_CONST_2)
+#define PRND_K1 (HSIPHASH_CONST_1 ^ HSIPHASH_CONST_3)

#else
#error Unsupported BITS_PER_LONG
--- a/include/linux/siphash.h
+++ b/include/linux/siphash.h
@@ -136,4 +136,32 @@ static inline u32 hsiphash(const void *d
return ___hsiphash_aligned(data, len, key);
}

+/*
+ * These macros expose the raw SipHash and HalfSipHash permutations.
+ * Do not use them directly! If you think you have a use for them,
+ * be sure to CC the maintainer of this file explaining why.
+ */
+
+#define SIPHASH_PERMUTATION(a, b, c, d) ( \
+ (a) += (b), (b) = rol64((b), 13), (b) ^= (a), (a) = rol64((a), 32), \
+ (c) += (d), (d) = rol64((d), 16), (d) ^= (c), \
+ (a) += (d), (d) = rol64((d), 21), (d) ^= (a), \
+ (c) += (b), (b) = rol64((b), 17), (b) ^= (c), (c) = rol64((c), 32))
+
+#define SIPHASH_CONST_0 0x736f6d6570736575ULL
+#define SIPHASH_CONST_1 0x646f72616e646f6dULL
+#define SIPHASH_CONST_2 0x6c7967656e657261ULL
+#define SIPHASH_CONST_3 0x7465646279746573ULL
+
+#define HSIPHASH_PERMUTATION(a, b, c, d) ( \
+ (a) += (b), (b) = rol32((b), 5), (b) ^= (a), (a) = rol32((a), 16), \
+ (c) += (d), (d) = rol32((d), 8), (d) ^= (c), \
+ (a) += (d), (d) = rol32((d), 7), (d) ^= (a), \
+ (c) += (b), (b) = rol32((b), 13), (b) ^= (c), (c) = rol32((c), 16))
+
+#define HSIPHASH_CONST_0 0U
+#define HSIPHASH_CONST_1 0U
+#define HSIPHASH_CONST_2 0x6c796765U
+#define HSIPHASH_CONST_3 0x74656462U
+
#endif /* _LINUX_SIPHASH_H */
--- a/lib/siphash.c
+++ b/lib/siphash.c
@@ -18,19 +18,13 @@
#include <asm/word-at-a-time.h>
#endif

-#define SIPROUND \
- do { \
- v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
- v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
- v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
- v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
- } while (0)
+#define SIPROUND SIPHASH_PERMUTATION(v0, v1, v2, v3)

#define PREAMBLE(len) \
- u64 v0 = 0x736f6d6570736575ULL; \
- u64 v1 = 0x646f72616e646f6dULL; \
- u64 v2 = 0x6c7967656e657261ULL; \
- u64 v3 = 0x7465646279746573ULL; \
+ u64 v0 = SIPHASH_CONST_0; \
+ u64 v1 = SIPHASH_CONST_1; \
+ u64 v2 = SIPHASH_CONST_2; \
+ u64 v3 = SIPHASH_CONST_3; \
u64 b = ((u64)(len)) << 56; \
v3 ^= key->key[1]; \
v2 ^= key->key[0]; \
@@ -389,19 +383,13 @@ u32 hsiphash_4u32(const u32 first, const
}
EXPORT_SYMBOL(hsiphash_4u32);
#else
-#define HSIPROUND \
- do { \
- v0 += v1; v1 = rol32(v1, 5); v1 ^= v0; v0 = rol32(v0, 16); \
- v2 += v3; v3 = rol32(v3, 8); v3 ^= v2; \
- v0 += v3; v3 = rol32(v3, 7); v3 ^= v0; \
- v2 += v1; v1 = rol32(v1, 13); v1 ^= v2; v2 = rol32(v2, 16); \
- } while (0)
+#define HSIPROUND HSIPHASH_PERMUTATION(v0, v1, v2, v3)

#define HPREAMBLE(len) \
- u32 v0 = 0; \
- u32 v1 = 0; \
- u32 v2 = 0x6c796765U; \
- u32 v3 = 0x74656462U; \
+ u32 v0 = HSIPHASH_CONST_0; \
+ u32 v1 = HSIPHASH_CONST_1; \
+ u32 v2 = HSIPHASH_CONST_2; \
+ u32 v3 = HSIPHASH_CONST_3; \
u32 b = ((u32)(len)) << 24; \
v3 ^= key->key[1]; \
v2 ^= key->key[0]; \

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