[crypto] Add rv_core_ibex function that checks CPUCTRL config

The CPUCTRL Ibex register contains two security-relevant entries
(dummy_instr_en and data_ind_timing). As these two security
features should be enabled when using CryptoLib, the newly added
function checks whether they are enabled.

Signed-off-by: Pascal Nasahl <[email protected]>

Author: nasahlpa

sw/device/lib/crypto/drivers/rv_core_ibex.c

@@ -25,8 +25,37 @@ enum {
    * CSR_REG_CPUCTRL[0] is the iCache configuration field.
    */
   kCpuctrlICacheMask = 1,
+  /**
+   * Mask for extracting cpuctrl_csr[1] and cpuctrl_csr[2] is 0b11.
+   */
+  kMask = 0x3,
+  /**
+   * The first item is cpuctrl_csr[1].
+   */
+  kIdx = 0x1,
+  /**
+   * cpuctrl_csr[1] and cpuctrl_csr[2] should be set to 0b11.
+   */
+  kExpectedConfig = 0x3,
 };
 
+hardened_bool_t ibex_check_security_config(void) {
+  uint32_t cpuctrl_csr;
+  CSR_READ(CSR_REG_CPUCTRL, &cpuctrl_csr);
+
+  // Check if cpuctrl_csr[1] (data_ind_timing) and cpuctrl_csr[2]
+  // (dummy_instr_en) is set to 1 (enabled).
+  bitfield_field32_t cpuctrl_mask = {.mask = kMask, .index = kIdx};
+  uint32_t cpuctrl_cfg = bitfield_field32_read(cpuctrl_csr, cpuctrl_mask);
+
+  if (launder32(cpuctrl_cfg) != kExpectedConfig) {
+    return kHardenedBoolFalse;
+  }
+  HARDENED_CHECK_EQ(cpuctrl_cfg, kExpectedConfig);
+
+  return kHardenedBoolTrue;
+}
+
 /**
  * Blocks until data is ready in the RND register.
  */

sw/device/lib/crypto/drivers/rv_core_ibex.h

@@ -31,6 +31,19 @@ status_t ibex_disable_icache(hardened_bool_t *icache_enabled);
  */
 void ibex_restore_icache(hardened_bool_t icache_enabled);
 
+/**
+ * Checks if the expected Ibex Security Features are enabled.
+ *
+ * This function reads Ibex cpuctrl register and checks, whether the following
+ * security features are enabled:
+ * - data_ind_timing
+ * - dummy_instr_en
+ *
+ * @returns Whether the config matches the expected secure config.
+ */
+OT_WARN_UNUSED_RESULT
+hardened_bool_t ibex_check_security_config(void);
+
 /**
  * Get random data from the EDN0 interface.
  *