From 392fa1ef6f9e5643eac0332a493fa02f3138de3c Mon Sep 17 00:00:00 2001
From: Paul Selkirk <paul@psgd.org>
Date: Mon, 4 May 2020 13:01:21 -0400
Subject: Re-enable support for HAL_MKM_FLASH_BACKUP_KLUDGE.

---
 keywrap.c | 44 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 11 deletions(-)

diff --git a/keywrap.c b/keywrap.c
index ccf7ea8..dc1c6ba 100644
--- a/keywrap.c
+++ b/keywrap.c
@@ -52,6 +52,7 @@ typedef union {
     uint32_t w;
 } byteword_t;
 
+
 /*
  * Match uninitialized flash for the "not set" value.
  * Leave some bits at 1 for the "set" value to allow
@@ -61,7 +62,7 @@ typedef union {
 #define MKM_STATUS_SET                  0x0000ffff
 #define MKM_STATUS_ERASED               0x00000000
 
-static hal_error_t mkm_status = HAL_ERROR_IMPOSSIBLE;
+static uint32_t mkm_status = MKM_STATUS_NOT_SET;
 
 
 static inline hal_error_t hal_io_cmd_read(const hal_core_t *core)
@@ -78,13 +79,13 @@ static inline hal_error_t hal_io_cmd_write(const hal_core_t *core)
 
 
 /*
- * Check the MKM status
+ * Check the MKM status word.
  */
 
 hal_error_t hal_keywrap_mkm_status(hal_core_t *core)
 {
   const int free_core = core == NULL;
-  uint8_t config[4] = { 0, 0, 0, 0 };
+  uint8_t config[4] = { 0 };
   byteword_t status;
   hal_error_t err;
 
@@ -102,17 +103,22 @@ hal_error_t hal_keywrap_mkm_status(hal_core_t *core)
   if (err != HAL_OK)
     return err;
 
-  switch (htonl(status.w)) {
-  case MKM_STATUS_SET:     return mkm_status = HAL_OK;
-  case MKM_STATUS_NOT_SET: return mkm_status = HAL_ERROR_MASTERKEY_NOT_SET;
-  default:                 return mkm_status = HAL_ERROR_MASTERKEY_FAIL;
+  switch (mkm_status = ntohl(status.w)) {
+  case MKM_STATUS_SET:     return HAL_OK;
+  case MKM_STATUS_NOT_SET: return HAL_ERROR_MASTERKEY_NOT_SET;
+  default:                 return HAL_ERROR_MASTERKEY_FAIL;
   }
 }
 
+
+/*
+ * Write a new KEK to the MKM.
+ */
+
 hal_error_t hal_keywrap_mkm_write(hal_core_t *core, const uint8_t *K, const size_t K_len)
 {
   const int free_core = core == NULL;
-  uint8_t config[4] = { 0, 0, 0, 0 };
+  uint8_t config[4] = { 0 };
   byteword_t status;
   hal_error_t err;
 
@@ -149,6 +155,8 @@ hal_error_t hal_keywrap_mkm_write(hal_core_t *core, const uint8_t *K, const size
       (err = hal_io_wait_ready(core))                                         != HAL_OK)
     goto out;
 
+  mkm_status = ntohl(status.w);
+
 out:
   if (free_core)
     hal_core_free(core);
@@ -156,10 +164,18 @@ out:
   return err;
 }
 
+
+/*
+ * Erase the KEK from the MKM.
+ */
+
 hal_error_t hal_keywrap_mkm_erase(hal_core_t *core, const size_t K_len)
 {
   uint8_t buf[KEK_LENGTH] = { 0 };
 
+  if (K_len != KEK_LENGTH)
+    return HAL_ERROR_MASTERKEY_BAD_LENGTH;
+
   return hal_keywrap_mkm_write(core, buf, sizeof(buf));
 }
 
@@ -208,9 +224,15 @@ static hal_error_t load_kek(hal_core_t *core, const uint8_t *K, const size_t K_l
 
   else {
     /* read the MKM KEK into the keywrap core */
-    if (mkm_status != HAL_OK &&
-        (err = hal_keywrap_mkm_status(core)) != HAL_OK)
+    if (mkm_status != MKM_STATUS_SET &&
+        (err = hal_keywrap_mkm_status(core)) != HAL_OK) {
+#if HAL_MKM_FLASH_BACKUP_KLUDGE
+      uint8_t kek[KEK_LENGTH];
+      if ((err = hal_mkm_flash_read_no_lock(kek, sizeof(kek))) == HAL_OK)
+        return load_kek(core, kek, sizeof(kek), action);
+#endif
       return err;
+    }
 
     config[3] &= ~KEYWRAP_CONFIG_MKS;
     if ((err = hal_io_write(core, KEYWRAP_ADDR_CONFIG, config, sizeof(config))) != HAL_OK ||
@@ -219,7 +241,7 @@ static hal_error_t load_kek(hal_core_t *core, const uint8_t *K, const size_t K_l
       return err;
 
     config[3] &= ~KEYWRAP_CONFIG_MKK;
-    config[3] |= KEYWRAP_CONFIG_KEYLEN;  /* XXX hardwire to 256-bits for now */
+    config[3] |= KEYWRAP_CONFIG_KEYLEN;  /* MKM KEK is required to be 256 bits */
   }
 
   switch (action) {
-- 
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