silence clib_mem_unaligned() invalid read found by address-sanitizer

clib_mem_unaligned + zap64 casts its input as u64, computes a mask
according to the input length, and returns the casted maked value.
Therefore all the 8 Bytes of the u64 are systematically read, and
the invalid ones are discarded.

Since they are discarded correctly, this invalid read can safely be
ignored.

Revert "fix clib_mem_unaligned() invalid read"
This reverts commit 0ed3d81a5fa274283ae69b69a405c385189897d3.

Change-Id: I5cc33ad36063c414085636debe93707d9a75157a
Signed-off-by: Gabriel Ganne <gabriel.ganne@enea.com>

1 files changed, 28 insertions, 19 deletions

diff --git a/src/vppinfra/hash.c b/src/vppinfra/hash.c
index b3db9f82b9c..121fa385705 100644
--- a/src/vppinfra/hash.c
+++ b/src/vppinfra/hash.c
@@ -80,27 +80,33 @@ static u8 *hash_format_pair_default (u8 * s, va_list * args);
 #if uword_bits == 64
 
 static inline u64
-get_unaligned_as_u64 (void const *data, int n)
+zap64 (u64 x, word n)
 {
-  int i;
-  u64 r = 0;
-  u8 const *p = (u8 const *) data;
-
+#define _(n) (((u64) 1 << (u64) (8*(n))) - (u64) 1)
+  static u64 masks_little_endian[] = {
+    0, _(1), _(2), _(3), _(4), _(5), _(6), _(7),
+  };
+  static u64 masks_big_endian[] = {
+    0, ~_(7), ~_(6), ~_(5), ~_(4), ~_(3), ~_(2), ~_(1),
+  };
+#undef _
   if (clib_arch_is_big_endian)
-    {
-      for (i = 0; i < n; i++)
-	r |= ((u64) ((*(p + i)) << (u8) (1 << (8 - i))));
-    }
+    return x & masks_big_endian[n];
   else
-    {
-      for (i = 0; i < n; i++)
-	r |= ((u64) ((*(p + i)) << (u8) (1 << i)));
-    }
-
-  return r;
+    return x & masks_little_endian[n];
 }
 
-static inline u64
+/**
+ * make address-sanitizer skip this:
+ * clib_mem_unaligned + zap64 casts its input as u64, computes a mask
+ * according to the input length, and returns the casted maked value.
+ * Therefore all the 8 Bytes of the u64 are systematically read, which
+ * rightfully causes address-sanitizer to raise an error on smaller inputs.
+ *
+ * However the invalid Bytes are discarded within zap64(), whicj is why
+ * this can be silenced safely.
+ */
+static inline u64 __attribute__ ((no_sanitize_address))
 hash_memory64 (void *p, word n_bytes, u64 state)
 {
   u64 *q = p;
@@ -126,16 +132,19 @@ hash_memory64 (void *p, word n_bytes, u64 state)
     case 2:
       a += clib_mem_unaligned (q + 0, u64);
       b += clib_mem_unaligned (q + 1, u64);
-      c += get_unaligned_as_u64 (q + 2, n % sizeof (u64)) << 8;
+      if (n % sizeof (u64))
+	c += zap64 (clib_mem_unaligned (q + 2, u64), n % sizeof (u64)) << 8;
       break;
 
     case 1:
       a += clib_mem_unaligned (q + 0, u64);
-      b += get_unaligned_as_u64 (q + 1, n % sizeof (u64));
+      if (n % sizeof (u64))
+	b += zap64 (clib_mem_unaligned (q + 1, u64), n % sizeof (u64));
       break;
 
     case 0:
-      a += get_unaligned_as_u64 (q + 0, n % sizeof (u64));
+      if (n % sizeof (u64))
+	a += zap64 (clib_mem_unaligned (q + 0, u64), n % sizeof (u64));
       break;
     }