hmac: Added Downstream JTAG enable mode for esp32c3

If JTAG is disabled temporarily by burning SOFT_DIS_JTAG, it can be
re-enabled temporarily through esp_hmac_jtag_enable API

components/esp32c3/esp_hmac.c

@@ -16,14 +16,20 @@
 #include "driver/periph_ctrl.h"
 #include "esp32c3/rom/hmac.h"
 #include "esp32c3/rom/ets_sys.h"
+#include "esp_efuse.h"
+#include "esp_efuse_table.h"
 #include "esp_hmac.h"
+#include "esp_log.h"
 #include "esp_crypto_lock.h"
+#include "soc/hwcrypto_reg.h"
 
 #include "hal/hmac_hal.h"
 
 #define SHA256_BLOCK_SZ 64
 #define SHA256_PAD_SZ 8
 
+static const char *TAG = "esp_hmac";
+
 /**
  * @brief Apply the HMAC padding without the embedded length.
  *
@@ -130,3 +136,53 @@ esp_err_t esp_hmac_calculate(hmac_key_id_t key_id,
 
     return ESP_OK;
 }
+
+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;
+}
+
+esp_err_t esp_hmac_jtag_enable(hmac_key_id_t key_id, const uint8_t *token)
+{
+    int ets_status;
+    esp_err_t err = ESP_OK;
+
+    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_DIS_PAD_JTAG)) {
+        ESP_LOGE(TAG, "JTAG disabled permanently.");
+        return ESP_FAIL;
+    }
+
+    esp_crypto_hmac_lock_acquire();
+
+    ets_status = ets_jtag_enable_temporarily(token, convert_key_type(key_id));
+
+    if (ets_status != ETS_OK) {
+        // ets_jtag_enable_temporarily returns either ETS_OK or ETS_FAIL
+        err = ESP_FAIL;
+        ESP_LOGE(TAG, "JTAG re-enabling failed (%d)", err);
+    }
+
+    ESP_LOGD(TAG, "HMAC computation in downstream mode is completed.");
+
+    ets_hmac_disable();
+
+    esp_crypto_hmac_lock_release();
+
+    return err;
+}
+
+esp_err_t esp_hmac_jtag_disable()
+{
+    esp_crypto_hmac_lock_acquire();
+
+    REG_SET_BIT(HMAC_SET_INVALIDATE_JTAG_REG, HMAC_INVALIDATE_JTAG);
+
+    esp_crypto_hmac_lock_release();
+
+    ESP_LOGD(TAG, "Invalidate JTAG result register. JTAG disabled.");
+
+    return ESP_OK;
+}

components/esp32c3/include/esp_hmac.h

@@ -60,6 +60,35 @@ 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 disabled by HW.
+ *        In downstream mode, HMAC calculations performed by peripheral are 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 enabled using the HMAC downstream mode. This function just clears the result generated
+ *         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