NetworkPkg/IScsiDxe: support SHA256 in CHAP

Insert a SHA256 CHAP_HASH structure at the start of "mChapHash".

Update ISCSI_CHAP_MAX_DIGEST_SIZE to SHA256_DIGEST_SIZE (32).

This enables the initiator and the target to negotiate SHA256 for CHAP, in
preference to MD5.

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3355
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Message-Id: <20210629163337.14120-6-lersek@redhat.com>

NetworkPkg/IScsiDxe/IScsiCHAP.c

@@ -15,6 +15,18 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 // by the initiator.
 //
 STATIC CONST CHAP_HASH mChapHash[] = {
+  {
+    ISCSI_CHAP_ALGORITHM_SHA256,
+    SHA256_DIGEST_SIZE,
+    Sha256GetContextSize,
+    Sha256Init,
+    Sha256Update,
+    Sha256Final
+  },
+  //
+  // Keep the deprecated MD5 entry at the end of the array (making MD5 the
+  // least preferred choice of the initiator).
+  //
   {
     ISCSI_CHAP_ALGORITHM_MD5,
     MD5_DIGEST_SIZE,

NetworkPkg/IScsiDxe/IScsiCHAP.h

@@ -22,12 +22,13 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 // https://www.iana.org/assignments/ppp-numbers/ppp-numbers.xhtml#ppp-numbers-9
 //
 #define ISCSI_CHAP_ALGORITHM_MD5                  5
+#define ISCSI_CHAP_ALGORITHM_SHA256               7
 
 //
 // Byte count of the largest digest over the above-listed
 // ISCSI_CHAP_ALGORITHM_* hash algorithms.
 //
-#define ISCSI_CHAP_MAX_DIGEST_SIZE                MD5_DIGEST_SIZE
+#define ISCSI_CHAP_MAX_DIGEST_SIZE                SHA256_DIGEST_SIZE
 
 #define ISCSI_CHAP_STEP_ONE                       1
 #define ISCSI_CHAP_STEP_TWO                       2