Merge pull request #571 from aidangarske/fenrir-fixes-9161-9162-9187

Fix wolfCrypt refcount race P521 primary derivation and policy session auth bypass

Author: dgarske

src/fwtpm/fwtpm_command.c

@@ -16811,6 +16811,10 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
             else if (entityH == TPM_RH_LOCKOUT) {
                 authPolicy = &ctx->lockoutPolicy;
             }
+            /* PCR handles: check PCR_SetAuthPolicy-assigned policy */
+            else if (entityH <= PCR_LAST) {
+                authPolicy = &ctx->pcrPolicy[entityH - PCR_FIRST];
+            }
 
             /* If entity has a non-empty authPolicy, it must match */
             if (authPolicy != NULL && authPolicy->size > 0) {
@@ -16870,6 +16874,18 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
                     TPM_ST_NO_SESSIONS, TPM_RC_POLICY_FAIL);
                 return TPM_RC_SUCCESS;
             }
+            else if (authPolicy == NULL) {
+                /* A policy session cannot authorize a handle whose authPolicy
+                 * cannot be resolved (for example hash/sign sequence handles);
+                 * fail closed per TPM 2.0 Part 1 Sec. 19.7. */
+            #ifdef DEBUG_WOLFTPM
+                printf("fwTPM: Policy session rejected for handle 0x%x with "
+                    "unresolved authPolicy (CC=0x%x)\n", entityH, cmdCode);
+            #endif
+                *rspSize = FwBuildErrorResponse(rspBuf, rspCap,
+                    TPM_ST_NO_SESSIONS, TPM_RC_POLICY_FAIL);
+                return TPM_RC_SUCCESS;
+            }
         }
     }
 

src/fwtpm/fwtpm_crypto.c

@@ -572,6 +572,53 @@ TPM_RC FwGenerateEccKey(WC_RNG* rng,
 /* ================================================================== */
 
 #ifdef HAVE_ECC
+/* Constant-time compare of two big-endian byte arrays of equal length.
+ * Returns 1 when a < b, otherwise 0. */
+static int FwCtLessBE(const byte* a, const byte* b, int len)
+{
+    int i;
+    unsigned int borrow = 0;
+    for (i = len - 1; i >= 0; i--) {
+        unsigned int diff = (unsigned int)a[i] - (unsigned int)b[i] - borrow;
+        borrow = (diff >> 8) & 1u;
+    }
+    return (int)borrow;
+}
+
+/* Load the curve order into a big-endian, keySz-padded buffer and report its
+ * bit length, used to bound and mask the derived scalar. */
+static TPM_RC FwEccGetCurveOrder(int wcCurve, byte* orderBuf, int keySz,
+    int* orderBits)
+{
+    TPM_RC rc = TPM_RC_SUCCESS;
+    int idx;
+    const ecc_set_type* dp;
+    mp_int order;
+
+    idx = wc_ecc_get_curve_idx(wcCurve);
+    if (idx < 0) {
+        return TPM_RC_CURVE;
+    }
+    dp = wc_ecc_get_curve_params(idx);
+    if (dp == NULL) {
+        return TPM_RC_CURVE;
+    }
+    if (mp_init(&order) != MP_OKAY) {
+        return TPM_RC_FAILURE;
+    }
+    if (mp_read_radix(&order, dp->order, MP_RADIX_HEX) != MP_OKAY) {
+        rc = TPM_RC_FAILURE;
+    }
+    if (rc == 0) {
+        *orderBits = mp_count_bits(&order);
+        if (mp_to_unsigned_bin_len(&order, orderBuf, keySz) != MP_OKAY) {
+            rc = TPM_RC_FAILURE;
+        }
+    }
+    mp_clear(&order);
+    return rc;
+}
+
 /* Derive ECC primary key from hierarchy seed per TPM 2.0 Part 1 Section 26.3.
  *   d = KDFa(nameAlg, seed, "ECC", hashUnique, counter, keySz*8)
  *   Q = d * G
@@ -596,6 +643,8 @@ TPM_RC FwDeriveEccPrimaryKey(TPMI_ALG_HASH nameAlg,
     int i;
     int allZero;
     volatile byte orAccum;
+    byte orderBuf[MAX_ECC_BYTES];
+    int orderBits = 0;
 
     FWTPM_ALLOC_VAR(eccKey, ecc_key);
 
@@ -604,6 +653,12 @@ TPM_RC FwDeriveEccPrimaryKey(TPMI_ALG_HASH nameAlg,
         return TPM_RC_CURVE;
     }
 
+    rc = FwEccGetCurveOrder(wcCurve, orderBuf, keySz, &orderBits);
+    if (rc != 0) {
+        FWTPM_FREE_VAR(eccKey);
+        return rc;
+    }
+
     /* Derive private scalar d via KDFa, retry if out of range */
     while (!valid && counter < 100) {
         FwStoreU32BE(counterBuf, counter);
@@ -615,14 +670,18 @@ TPM_RC FwDeriveEccPrimaryKey(TPMI_ALG_HASH nameAlg,
             rc = TPM_RC_FAILURE;
             break;
         }
-        /* Constant-time check d != 0 (all zeros) */
+        /* Mask unused high bits so the candidate matches the order bit length */
+        if ((orderBits & 7) != 0) {
+            dBuf[0] &= (byte)((1u << (orderBits & 7)) - 1u);
+        }
+        /* Constant-time check 0 < d < order */
         orAccum = 0;
         for (i = 0; i < keySz; i++) {
             orAccum |= dBuf[i];
         }
         allZero = (orAccum == 0);
-        if (!allZero) {
-            valid = 1; /* Accept — range check done by import */
+        if (!allZero && FwCtLessBE(dBuf, orderBuf, keySz)) {
+            valid = 1;
         }
         counter++;
     }

src/tpm2.c

@@ -690,6 +690,14 @@ static inline int TPM2_WolfCrypt_Init(void)
 {
     int rc = 0;
 
+#if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
+    defined(WOLFSSL_MUTEX_INITIALIZER)
+    /* gHwLock is statically initialized, so it can guard the reference count
+     * before wolfCrypt is initialized */
+    if (wc_LockMutex(&gHwLock) != 0)
+        return TPM_RC_FAILURE;
+#endif
+
     /* track reference count for wolfCrypt initialization */
     if (gWolfCryptRefCount == 0) {
     #ifdef DEBUG_WOLFSSL
@@ -710,8 +718,40 @@ static inline int TPM2_WolfCrypt_Init(void)
     }
     gWolfCryptRefCount++;
 
+#if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
+    defined(WOLFSSL_MUTEX_INITIALIZER)
+    wc_UnLockMutex(&gHwLock);
+#endif
+
     return rc;
 }
+
+static inline void TPM2_WolfCrypt_Cleanup(void)
+{
+#if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
+    defined(WOLFSSL_MUTEX_INITIALIZER)
+    int locked = (wc_LockMutex(&gHwLock) == 0);
+#endif
+
+    /* track wolf initialize reference count in wolfTPM. wolfCrypt does not
+     * properly track reference count in v4.1 or older releases */
+    gWolfCryptRefCount--;
+    if (gWolfCryptRefCount < 0)
+        gWolfCryptRefCount = 0;
+    if (gWolfCryptRefCount == 0) {
+    #if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
+        !defined(WOLFSSL_MUTEX_INITIALIZER)
+        wc_FreeMutex(&gHwLock);
+    #endif
+        wolfCrypt_Cleanup();
+    }
+
+#if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
+    defined(WOLFSSL_MUTEX_INITIALIZER)
+    if (locked)
+        wc_UnLockMutex(&gHwLock);
+#endif
+}
 #endif
 
 /******************************************************************************/
@@ -957,18 +997,7 @@ TPM_RC TPM2_Cleanup(TPM2_CTX* ctx)
     }
     #endif
 
-    /* track wolf initialize reference count in wolfTPM. wolfCrypt does not
-     * properly track reference count in v4.1 or older releases */
-    gWolfCryptRefCount--;
-    if (gWolfCryptRefCount < 0)
-        gWolfCryptRefCount = 0;
-    if (gWolfCryptRefCount == 0) {
-    #if !defined(WOLFTPM_NO_LOCK) && !defined(SINGLE_THREADED) && \
-        !defined(WOLFSSL_MUTEX_INITIALIZER)
-        wc_FreeMutex(&gHwLock);
-    #endif
-        wolfCrypt_Cleanup();
-    }
+    TPM2_WolfCrypt_Cleanup();
 #endif /* !WOLFTPM2_NO_WOLFCRYPT */
 
 #if (defined(WOLFTPM_LINUX_DEV) || defined(WOLFTPM_LINUX_DEV_AUTODETECT)) \