x86, setup: Fix EDD3.0 data verification.

Check for nonzero path in edd_has_edd30() has no sense. First, it looks
at the wrong memory. Device path starts at offset 30 of the info->params
structure which is at offset 8 from the beginning of info structure,
but code looks at info + 4 instead. This was correct when code was
introduced, but around v2.6.4 three more fields were added to edd_info
structure (commit 66b61a5c in history.git). Second, even if it will check
correct memory it will always succeed since at offset 30 (params->key)
there will be non-zero values otherwise previous check would fail.

The patch replaces this bogus check with one that verifies checksum.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Link: http://lkml.kernel.org/r/20110426082132.GG2265@redhat.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

drivers/firmware/edd.c

@@ -531,8 +531,8 @@ static int
 edd_has_edd30(struct edd_device *edev)
 {
 	struct edd_info *info;
-	int i, nonzero_path = 0;
-	char c;
+	int i;
+	u8 csum = 0;
 
 	if (!edev)
 		return 0;
@@ -544,16 +544,16 @@ edd_has_edd30(struct edd_device *edev)
 		return 0;
 	}
 
-	for (i = 30; i <= 73; i++) {
-		c = *(((uint8_t *) info) + i + 4);
-		if (c) {
-			nonzero_path++;
-			break;
-		}
-	}
-	if (!nonzero_path) {
+
+	/* We support only T13 spec */
+	if (info->params.device_path_info_length != 44)
+		return 0;
+
+	for (i = 30; i < info->params.device_path_info_length + 30; i++)
+		csum += *(((u8 *)&info->params) + i);
+
+	if (csum)
 		return 0;
-	}
 
 	return 1;
 }