HMAC: adding downstream JTAG Re-enable support

Closes IDF-802

components/esp32s2/esp_hmac.c

@@ -12,9 +12,17 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <string.h>
 #include "esp32s2/rom/hmac.h"
 #include "esp_hmac.h"
 #include "esp_crypto_lock.h"
+#include "esp_efuse.h"
+#include "esp_efuse_table.h"
+#include "soc/hwcrypto_reg.h"
+#include "soc/system_reg.h"
+#include "esp_log.h"
+
+static const char *TAG = "esp_hmac";
 
 static ets_efuse_block_t convert_key_type(hmac_key_id_t key_id) {
     return ETS_EFUSE_BLOCK_KEY0 + (ets_efuse_block_t) key_id;
@@ -44,3 +52,55 @@ esp_err_t esp_hmac_calculate(hmac_key_id_t key_id,
     }
 
 }
+
+esp_err_t esp_hmac_jtag_enable(hmac_key_id_t key_id, const uint8_t *token)
+{
+    esp_err_t err;
+
+    if ((!token) || (key_id >= HMAC_KEY_MAX))
+        return ESP_ERR_INVALID_ARG;
+
+    /* Check if JTAG is permanently disabled by HW Disable eFuse */
+    if (esp_efuse_read_field_bit(ESP_EFUSE_HARD_DIS_JTAG)) {
+        ESP_LOGE(TAG, "JTAG disabled permanently.");
+        return ESP_FAIL;
+    }
+
+    esp_crypto_dma_lock_acquire();
+
+    ets_hmac_enable();
+
+    /* Token updating into HMAC module. */
+    for (int i = 0; i < 32; i += 4) {
+        uint32_t key_word;
+        memcpy(&key_word, &token[i], 4);
+        REG_WRITE(DPORT_JTAG_CTRL_0_REG + i, __builtin_bswap32(key_word));
+    }
+
+    err = ets_hmac_calculate_downstream(convert_key_type(key_id), ETS_EFUSE_KEY_PURPOSE_HMAC_DOWN_JTAG);
+    if (err != ETS_OK) {
+        ESP_LOGE(TAG, "HMAC downstream JTAG enable mode setting failed.");
+        return ESP_FAIL;
+    }
+
+    ESP_LOGD(TAG, "HMAC computation in downstream mode is completed.");
+
+    ets_hmac_disable();
+
+    esp_crypto_dma_lock_release();
+
+    return ESP_OK;
+}
+
+esp_err_t esp_hmac_jtag_disable()
+{
+    esp_crypto_dma_lock_acquire();
+
+    REG_WRITE(HMAC_SET_INVALIDATE_JTAG_REG, 1);
+
+    esp_crypto_dma_lock_release();
+
+    ESP_LOGD(TAG, "Invalidate JTAG result register. JTAG disabled.");
+
+    return ESP_OK;
+}

components/esp32s2/include/esp_hmac.h

@@ -60,6 +60,38 @@ esp_err_t esp_hmac_calculate(hmac_key_id_t key_id,
         size_t message_len,
         uint8_t *hmac);
 
+/**
+ * @brief
+ * Use HMAC peripheral in Downstream mode to re-enable the JTAG, if it is not permanently disable by HW.
+ * In downstream mode HMAC calculations perfomred by peripheral used internally and not provided back to user.
+ *
+ * @param key_id Determines which of the 6 key blocks in the efuses should be used for the HMAC calculation.
+ *        The corresponding purpose field of the key block in the efuse must be set to HMAC downstream purpose.
+ *
+ * @param token Pre calculated HMAC value of the 32-byte 0x00 using SHA-256 and the known private HMAC key. The key is already
+ *        programmed to a eFuse key block. The key block number is provided as the first parameter to this function.
+ *
+ * @return
+ *      * ESP_OK, if the calculation was successful,
+ *                if the calculated HMAC value matches with provided token,
+ *                JTAG will be re-enable otherwise JTAG will remain disabled.
+ *                Return value does not indicate the JTAG status.
+ *      * ESP_FAIL, if the hmac calculation failed or JTAG is permanently disabled by EFUSE_HARD_DIS_JTAG eFuse parameter.
+ *      * ESP_ERR_INVALID_ARG, invalid input arguments
+ */
+esp_err_t esp_hmac_jtag_enable(hmac_key_id_t key_id,
+        const uint8_t *token);
+
+/**
+ *  @brief
+ *  Disable the JTAG which might be enable using the HMAC downstream mode. This function just clear the result generated by
+ *  JTAG key by calling esp_hmac_jtag_enable() API.
+ *
+ *  @return
+ *       * ESP_OK return ESP_OK after writing the HMAC_SET_INVALIDATE_JTAG_REG with value 1.
+ */
+esp_err_t esp_hmac_jtag_disable(void);
+
 #ifdef __cplusplus
 }
 #endif