target/arm: Implement an IMPDEF pauth algorithm

Without hardware acceleration, a cryptographically strong
algorithm is too expensive for pauth_computepac.

Even with hardware accel, we are not currently expecting
to link the linux-user binaries to any crypto libraries,
and doing so would generally make the --static build fail.

So choose XXH64 as a reasonably quick and decent hash.

Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210111235740.462469-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 98 insertions, 0 deletions

diff --git a/include/qemu/xxhash.h b/include/qemu/xxhash.h
index 076f1f6054..c2dcccadbf 100644
--- a/include/qemu/xxhash.h
+++ b/include/qemu/xxhash.h
@@ -119,4 +119,102 @@ static inline uint32_t qemu_xxhash6(uint64_t ab, uint64_t cd, uint32_t e,
     return qemu_xxhash7(ab, cd, e, f, 0);
 }
 
+/*
+ * Component parts of the XXH64 algorithm from
+ * https://github.com/Cyan4973/xxHash/blob/v0.8.0/xxhash.h
+ *
+ * The complete algorithm looks like
+ *
+ *  i = 0;
+ *  if (len >= 32) {
+ *      v1 = seed + XXH_PRIME64_1 + XXH_PRIME64_2;
+ *      v2 = seed + XXH_PRIME64_2;
+ *      v3 = seed + 0;
+ *      v4 = seed - XXH_PRIME64_1;
+ *      do {
+ *          v1 = XXH64_round(v1, get64bits(input + i));
+ *          v2 = XXH64_round(v2, get64bits(input + i + 8));
+ *          v3 = XXH64_round(v3, get64bits(input + i + 16));
+ *          v4 = XXH64_round(v4, get64bits(input + i + 24));
+ *      } while ((i += 32) <= len);
+ *      h64 = XXH64_mergerounds(v1, v2, v3, v4);
+ *  } else {
+ *      h64 = seed + XXH_PRIME64_5;
+ *  }
+ *  h64 += len;
+ *
+ *  for (; i + 8 <= len; i += 8) {
+ *      h64 ^= XXH64_round(0, get64bits(input + i));
+ *      h64 = rol64(h64, 27) * XXH_PRIME64_1 + XXH_PRIME64_4;
+ *  }
+ *  for (; i + 4 <= len; i += 4) {
+ *      h64 ^= get32bits(input + i) * PRIME64_1;
+ *      h64 = rol64(h64, 23) * XXH_PRIME64_2 + XXH_PRIME64_3;
+ *  }
+ *  for (; i < len; i += 1) {
+ *      h64 ^= get8bits(input + i) * XXH_PRIME64_5;
+ *      h64 = rol64(h64, 11) * XXH_PRIME64_1;
+ *  }
+ *
+ *  return XXH64_avalanche(h64)
+ *
+ * Exposing the pieces instead allows for simplified usage when
+ * the length is a known constant and the inputs are in registers.
+ */
+#define XXH_PRIME64_1   0x9E3779B185EBCA87ULL
+#define XXH_PRIME64_2   0xC2B2AE3D27D4EB4FULL
+#define XXH_PRIME64_3   0x165667B19E3779F9ULL
+#define XXH_PRIME64_4   0x85EBCA77C2B2AE63ULL
+#define XXH_PRIME64_5   0x27D4EB2F165667C5ULL
+
+static inline uint64_t XXH64_round(uint64_t acc, uint64_t input)
+{
+    return rol64(acc + input * XXH_PRIME64_2, 31) * XXH_PRIME64_1;
+}
+
+static inline uint64_t XXH64_mergeround(uint64_t acc, uint64_t val)
+{
+    return (acc ^ XXH64_round(0, val)) * XXH_PRIME64_1 + XXH_PRIME64_4;
+}
+
+static inline uint64_t XXH64_mergerounds(uint64_t v1, uint64_t v2,
+                                         uint64_t v3, uint64_t v4)
+{
+    uint64_t h64;
+
+    h64 = rol64(v1, 1) + rol64(v2, 7) + rol64(v3, 12) + rol64(v4, 18);
+    h64 = XXH64_mergeround(h64, v1);
+    h64 = XXH64_mergeround(h64, v2);
+    h64 = XXH64_mergeround(h64, v3);
+    h64 = XXH64_mergeround(h64, v4);
+
+    return h64;
+}
+
+static inline uint64_t XXH64_avalanche(uint64_t h64)
+{
+    h64 ^= h64 >> 33;
+    h64 *= XXH_PRIME64_2;
+    h64 ^= h64 >> 29;
+    h64 *= XXH_PRIME64_3;
+    h64 ^= h64 >> 32;
+    return h64;
+}
+
+static inline uint64_t qemu_xxhash64_4(uint64_t a, uint64_t b,
+                                       uint64_t c, uint64_t d)
+{
+    uint64_t v1 = QEMU_XXHASH_SEED + XXH_PRIME64_1 + XXH_PRIME64_2;
+    uint64_t v2 = QEMU_XXHASH_SEED + XXH_PRIME64_2;
+    uint64_t v3 = QEMU_XXHASH_SEED + 0;
+    uint64_t v4 = QEMU_XXHASH_SEED - XXH_PRIME64_1;
+
+    v1 = XXH64_round(v1, a);
+    v2 = XXH64_round(v2, b);
+    v3 = XXH64_round(v3, c);
+    v4 = XXH64_round(v4, d);
+
+    return XXH64_avalanche(XXH64_mergerounds(v1, v2, v3, v4));
+}
+
 #endif /* QEMU_XXHASH_H */