fwTPM: TPM_CAP_TPM_PROPERTIES leaves out fixed properties, including TPM_PT_CONTEXT_SYM_SIZE #651

TPM2_GetCapability(TPM_CAP_TPM_PROPERTIES, TPM_PT_FIXED, ...) returns 19 fixed properties. It leaves out, among others:

• TPM_PT_VENDOR_TPM_TYPE (0x10a);
• TPM_PT_HR_TRANSIENT_MIN, TPM_PT_HR_PERSISTENT_MIN, TPM_PT_HR_LOADED_MIN and TPM_PT_ACTIVE_SESSIONS_MAX (0x10e–0x111);
• TPM_PT_PCR_SELECT_MIN (0x113) and TPM_PT_CONTEXT_GAP_MAX (0x114);
• TPM_PT_NV_COUNTERS_MAX through TPM_PT_ORDERLY_COUNT (0x116–0x11d), which includes TPM_PT_CONTEXT_SYM and TPM_PT_CONTEXT_SYM_SIZE;
• TPM_PT_MAX_OBJECT_CONTEXT, TPM_PT_MAX_SESSION_CONTEXT and the TPM_PT_PS_* properties (0x121–0x128).

The TCG reference implementation and libtpms report every fixed property, and clients read them:

• tpm2-pkcs11 sizes AES keys from TPM_PT_CONTEXT_SYM_SIZE, so without it every AES key generation or import is refused.
• Clients that index the reply by offset from TPM_PT_FIXED, as tpm2-pkcs11's C_GetTokenInfo did, read the wrong values once one is missing (here, everything after 0x10a moves up by one).
• Resource managers use TPM_PT_HR_*_MIN and TPM_PT_ACTIVE_SESSIONS_MAX.

Reproduction. Call Esys_GetCapability(TPM2_CAP_TPM_PROPERTIES, TPM2_PT_FIXED, TPM2_MAX_TPM_PROPERTIES) and list the tags:

fwTPM master: 0x100-0x109 0x10b 0x10c 0x10d 0x112 0x11e 0x11f 0x120 0x129 0x12d   (19)
swtpm 0.10.2: 0x100-0x12e, 46 fixed properties, including 0x10a and 0x11c

Suggested fix. Report the remaining fixed properties from the build's limits (FWTPM_MAX_OBJECTS, the session and NV limits, the context-protection algorithm and its key size: AES and 128 or 256 bits). TPM_PT_CONTEXT_SYM_SIZE matters most for clients.

Environment

• wolfTPM master at d7f73b5 (also seen in v4.2.0), fwTPM built with ./configure --enable-fwtpm-only --enable-swtpm on wolfSSL v5.9.4-stable (--enable-wolftpm --enable-pkcallbacks --enable-keygen).
• fwtpm_server --port 2341 --platform-port 2342, reached through the tpm2-tss 4.2.0 swtpm TCTI (swtpm:host=127.0.0.1,port=2341).
• For comparison, the same program against swtpm 0.10.2 (libtpms).
• Found while running tpm2-pkcs11 on fwTPM.