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Reject storage keys in fwTPM decrypt commands and bind split param-enc sessions #622

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Merged
dgarske merged 3 commits into from
Oct 5, 2026
Merged

Reject storage keys in fwTPM decrypt commands and bind split param-enc sessions #622

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e8ce5d3
F-14695 - Reject storage keys in fwTPM RSA_Decrypt and ZGen commands
aidangarske Oct 5, 2026
2482167
F-14680 - Honor split param-enc sessions and bind them to the auth HMAC
aidangarske Oct 5, 2026
cf87eec
Clarify the bind parameter comment in the param-enc auth test
aidangarske Oct 5, 2026
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111 changes: 80 additions & 31 deletions src/fwtpm/fwtpm_command.c
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Original file line number Diff line number Diff line change
Expand Up @@ -843,6 +843,7 @@ static int FwComputeCpHash(TPMI_ALG_HASH hashAlg, TPM_CC cmdCode,
static int FwComputeSessionHmac(FWTPM_Session* sess,
const byte* pHash, int pHashSz, UINT8 sessionAttributes,
const byte* authValue, int authValueSz,
const TPM2B_NONCE* nonceDecrypt, const TPM2B_NONCE* nonceEncrypt,
int isResponse,
byte* hmacOut, int* hmacOutSz)
{
Expand Down Expand Up @@ -898,6 +899,13 @@ static int FwComputeSessionHmac(FWTPM_Session* sess,
if (rc == 0)
rc = wc_HmacUpdate(hmac, sess->nonceTPM.buffer,
sess->nonceTPM.size);
/* Binds separate decrypt/encrypt sessions to the first auth session */
if (rc == 0 && nonceDecrypt != NULL)
rc = wc_HmacUpdate(hmac, nonceDecrypt->buffer,
nonceDecrypt->size);
if (rc == 0 && nonceEncrypt != NULL)
rc = wc_HmacUpdate(hmac, nonceEncrypt->buffer,
nonceEncrypt->size);
}

/* sessionAttributes (1 byte) */
Expand Down Expand Up @@ -9359,6 +9367,11 @@ static TPM_RC FwCmd_RSA_Decrypt(FWTPM_CTX* ctx, TPM2_Packet* cmd,
if (!(obj->pub.objectAttributes & TPMA_OBJECT_decrypt))
rc = TPM_RC_KEY;
}
/* Storage keys must not act as a raw decryption oracle (Part 3 Sec.14.3) */
if (rc == 0) {
if ((obj->pub.objectAttributes & TPMA_OBJECT_restricted) != 0)
rc = TPM_RC_ATTRIBUTES;
}
if (rc == 0) {
if (obj->privKeySize == 0) {
rc = TPM_RC_KEY; /* need private key */
Expand Down Expand Up @@ -10552,10 +10565,12 @@ static TPM_RC FwCmd_ECDH_ZGen(FWTPM_CTX* ctx, TPM2_Packet* cmd,
rc = TPM_RC_KEY;
}
}
/* Key agreement requires a decryption key (Part 3 Sec.21.3) */
/* Key agreement requires an unrestricted decryption key (Part 3 Sec.14.5) */
if (rc == 0) {
if (!(obj->pub.objectAttributes & TPMA_OBJECT_decrypt))
if ((obj->pub.objectAttributes & TPMA_OBJECT_restricted) != 0 ||
(obj->pub.objectAttributes & TPMA_OBJECT_decrypt) == 0) {
rc = TPM_RC_ATTRIBUTES;
}
}

/* Skip auth area */
Expand Down Expand Up @@ -16679,8 +16694,10 @@ static TPM_RC FwCmd_ZGen_2Phase(FWTPM_CTX* ctx, TPM2_Packet* cmd,
if (rc == 0 && keyA->pub.type != TPM_ALG_ECC) {
rc = TPM_RC_KEY;
}
/* Key agreement requires a decryption key (Part 3 Sec.14.7) */
if (rc == 0 && !(keyA->pub.objectAttributes & TPMA_OBJECT_decrypt)) {
/* Key agreement requires an unrestricted decryption key (Part 3 Sec.14.7) */
if (rc == 0 &&
((keyA->pub.objectAttributes & TPMA_OBJECT_restricted) != 0 ||
(keyA->pub.objectAttributes & TPMA_OBJECT_decrypt) == 0)) {
rc = TPM_RC_ATTRIBUTES;
}

Expand Down Expand Up @@ -19510,7 +19527,9 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
const FWTPM_CMD_ENTRY* entry;
TPM_RC rc = TPM_RC_SUCCESS;
#ifndef FWTPM_NO_PARAM_ENC
FWTPM_Session* encSess = NULL; /* Session requesting param encryption */
FWTPM_Session* decSess = NULL; /* Session with the decrypt attribute */
TPM_HANDLE decAuthHandle = 0; /* Handle the decrypt session authorizes */
FWTPM_Session* encSess = NULL; /* Session with the encrypt attribute */
TPM_HANDLE encAuthHandle = 0; /* Handle the encrypt session authorizes */
int doEncCmd = 0; /* Decrypt incoming encrypted param */
int doEncRsp = 0; /* Encrypt outgoing response param */
Expand Down Expand Up @@ -19746,34 +19765,47 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
}

#ifndef FWTPM_NO_PARAM_ENC
/* Detect encryption session (first non-PW with a
* symmetric alg). Unsalted/unbound sessions are
* accepted for client compatibility; over the
* loopback transport their key is only observable
* to a local peer. */
if (encSess == NULL &&
sess->symmetric.algorithm != TPM_ALG_NULL) {
encSess = sess;
/* The first authHandleCnt handles are the ones
* that require authorization, in order, so auth
* session i authorizes handle i for
* i < authHandleCnt. Beyond that the session is
* a secondary encrypt-only session and
* authorizes no handle. */
/* decrypt/encrypt each pick the one session with
* that attribute and a cipher. Unsalted sessions
* stay accepted for client compatibility. */
if (((attribs & TPMA_SESSION_decrypt) != 0 &&
decSess != NULL) ||
((attribs & TPMA_SESSION_encrypt) != 0 &&
encSess != NULL)) {
rc = TPM_RC_ATTRIBUTES;
break;
}
if ((attribs & (TPMA_SESSION_decrypt |
TPMA_SESSION_encrypt)) != 0 &&
sess->symmetric.algorithm == TPM_ALG_NULL) {
rc = TPM_RC_SYMMETRIC;
break;
}
/* The first authHandleCnt handles are the ones
* that require authorization, in order, so auth
* session i authorizes handle i for
* i < authHandleCnt. Beyond that the session is
* a secondary encrypt-only session and
* authorizes no handle. */
/* decrypt attr = client encrypted cmd param */
if ((attribs & TPMA_SESSION_decrypt) != 0) {
decSess = sess;
if (cmdAuthCnt < (int)entry->authHandleCnt &&
cmdAuthCnt < cmdHandleCnt) {
encAuthHandle = cmdHandles[cmdAuthCnt];
decAuthHandle = cmdHandles[cmdAuthCnt];
}
/* decrypt attr = client encrypted cmd param */
if ((attribs & TPMA_SESSION_decrypt)
&&
(entry->encDecFlags & FW_CMD_FLAG_ENC)) {
if (entry->encDecFlags & FW_CMD_FLAG_ENC) {
doEncCmd = 1;
}
/* encrypt attr = TPM encrypts rsp param */
if ((attribs & TPMA_SESSION_encrypt)
&&
(entry->encDecFlags & FW_CMD_FLAG_DEC)) {
}
/* encrypt attr = TPM encrypts rsp param */
if ((attribs & TPMA_SESSION_encrypt) != 0) {
encSess = sess;
if (cmdAuthCnt < (int)entry->authHandleCnt &&
cmdAuthCnt < cmdHandleCnt) {
encAuthHandle = cmdHandles[cmdAuthCnt];
}
if (entry->encDecFlags & FW_CMD_FLAG_DEC) {
doEncRsp = 1;
}
}
Expand Down Expand Up @@ -20317,11 +20349,27 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
int expectedSz = 0;
const byte* authVal = NULL;
int authValSz = 0;
const TPM2B_NONCE* nonceDecrypt = NULL;
const TPM2B_NONCE* nonceEncrypt = NULL;
TPM_HANDLE entityH;
int sizeMismatch;
int hmacDiff;
word32 cmpSz;

#ifndef FWTPM_NO_PARAM_ENC
/* Part 1 Sec.19.6.5: the first session's HMAC also covers the
* nonceTPM of a different decrypt and encrypt session */
if (hj == 0) {
if (decSess != NULL && decSess != hSess) {
nonceDecrypt = &decSess->nonceTPM;
}
if (encSess != NULL && encSess != hSess &&
encSess != decSess) {
nonceEncrypt = &encSess->nonceTPM;
}
}
#endif

/* Compute cpHash = H(commandCode || handleNames || cpBuffer) */
if (FwComputeCpHash(hSess->authHash, cmdCode,
cmdBuf, cmdSize, cmdHandles, cmdHandleCnt,
Expand Down Expand Up @@ -20385,6 +20433,7 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
/* Compute expected command HMAC (nonceCaller first, then nonceTPM) */
FwComputeSessionHmac(hSess, cpHash, cpHashSz,
cmdAuths[hj].attributes, authVal, authValSz,
nonceDecrypt, nonceEncrypt,
0, /* isResponse=0 for command HMAC */
expectedHmac, &expectedSz);

Expand Down Expand Up @@ -20430,11 +20479,11 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
/* Command parameter decryption (after HMAC verification, before handler).
* Per TPM 2.0 spec Part 1 Section 19.6.5: cpHash is computed over the encrypted
* command parameters. Decryption happens after HMAC verification. */
if (doEncCmd && encSess != NULL && cpStart > 0 && cpStart + 2 <= cmdSize) {
if (doEncCmd && decSess != NULL && cpStart > 0 && cpStart + 2 <= cmdSize) {
UINT16 paramSz;
paramSz = FwLoadU16BE(cmdBuf + cpStart);
if (paramSz > 0 && cpStart + 2 + paramSz <= cmdSize) {
rc = (TPM_RC)FwParamDecryptCmd(ctx, encSess, encAuthHandle,
rc = (TPM_RC)FwParamDecryptCmd(ctx, decSess, decAuthHandle,
(byte*)cmdBuf + cpStart + 2, paramSz);
if (rc != 0) {
#ifdef DEBUG_WOLFTPM
Expand Down Expand Up @@ -20642,7 +20691,7 @@ int FWTPM_ProcessCommand(FWTPM_CTX* ctx,
authValSz = 0;
}
FwComputeSessionHmac(sess, rpHash, rpHashSz, rspAttribs,
authVal, authValSz, 1 /* isResponse */,
authVal, authValSz, NULL, NULL, 1 /* isResponse */,
hmacBuf, &hmacSz);
}
TPM2_Packet_AppendU16(&rspPkt, (UINT16)hmacSz);
Expand Down
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