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mbedtls_ssl_config: Replace bit-fields by separate bytes

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This slightly increases the RAM consumption per context, but saves code
size on architectures with an instruction for direct byte access (which is
most of them).

Although this is technically an API break, in practice, a realistic
application won't break: it would have had to bypass API functions and rely
on the field size (e.g. relying on -1 == 1 in a 1-bit field).

Results (arm-none-eabi-gcc 7.3.1, build_arm_none_eabi_gcc_m0plus build):
library/ssl_cli.o: 19952 -> 19900 (diff: 52)
library/ssl_msg.o: 25810 -> 25798 (diff: 12)
library/ssl_srv.o: 22371 -> 22299 (diff: 72)
library/ssl_tls.o: 23274 -> 23038 (diff: 236)

Results (same architecture, config-suite-b.h + MBEDTLS_ECDH_LEGACY_CONTEXT +
MBEDTLS_ECP_RESTARTABLE):
library/ssl_cli.o: 2868 -> 2848 (diff: 20)
library/ssl_msg.o: 2916 -> 2924 (diff: -8)
library/ssl_srv.o: 3204 -> 3184 (diff: 20)
library/ssl_tls.o: 5860 -> 5756 (diff: 104)

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-11-16 18:31:46 +01:00
parent 9a0e0affef
commit 7f03d9ecc6
1 changed files with 21 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
include/mbedtls/ssl.h
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@ -1032,56 +1032,58 @@ struct mbedtls_ssl_config
unsigned char min_minor_ver; /*!< min. minor version used */
/*
* Flags (bitfields)
* Flags (could be bit-fields to save RAM, but separate bytes make
* the code smaller on architectures with an instruction for direct
* byte access).
*/
unsigned int endpoint : 1; /*!< 0: client, 1: server */
unsigned int transport : 1; /*!< stream (TLS) or datagram (DTLS) */
unsigned int authmode : 2; /*!< MBEDTLS_SSL_VERIFY_XXX */
uint8_t endpoint /*bool*/; /*!< 0: client, 1: server */
uint8_t transport /*bool*/; /*!< stream (TLS) or datagram (DTLS) */
uint8_t authmode /*2 bits*/; /*!< MBEDTLS_SSL_VERIFY_XXX */
/* needed even with renego disabled for LEGACY_BREAK_HANDSHAKE */
unsigned int allow_legacy_renegotiation : 2 ; /*!< MBEDTLS_LEGACY_XXX */
uint8_t allow_legacy_renegotiation /*2 bits*/; /*!< MBEDTLS_LEGACY_XXX */
#if defined(MBEDTLS_ARC4_C)
unsigned int arc4_disabled : 1; /*!< blacklist RC4 ciphersuites? */
uint8_t arc4_disabled /*bool*/; /*!< blacklist RC4 ciphersuites? */
#endif
#if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
unsigned int mfl_code : 3; /*!< desired fragment length */
uint8_t mfl_code /*3 bits*/; /*!< desired fragment length */
#endif
#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
unsigned int encrypt_then_mac : 1 ; /*!< negotiate encrypt-then-mac? */
uint8_t encrypt_then_mac /*bool*/; /*!< negotiate encrypt-then-mac? */
#endif
#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
unsigned int extended_ms : 1; /*!< negotiate extended master secret? */
uint8_t extended_ms /*bool*/; /*!< negotiate extended master secret? */
#endif
#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
unsigned int anti_replay : 1; /*!< detect and prevent replay? */
uint8_t anti_replay /*bool*/; /*!< detect and prevent replay? */
#endif
#if defined(MBEDTLS_SSL_CBC_RECORD_SPLITTING)
unsigned int cbc_record_splitting : 1; /*!< do cbc record splitting */
uint8_t cbc_record_splitting /*bool*/; /*!< do cbc record splitting */
#endif
#if defined(MBEDTLS_SSL_RENEGOTIATION)
unsigned int disable_renegotiation : 1; /*!< disable renegotiation? */
uint8_t disable_renegotiation /*bool*/; /*!< disable renegotiation? */
#endif
#if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
unsigned int trunc_hmac : 1; /*!< negotiate truncated hmac? */
uint8_t trunc_hmac /*bool*/; /*!< negotiate truncated hmac? */
#endif
#if defined(MBEDTLS_SSL_SESSION_TICKETS)
unsigned int session_tickets : 1; /*!< use session tickets? */
uint8_t session_tickets /*bool*/; /*!< use session tickets? */
#endif
#if defined(MBEDTLS_SSL_FALLBACK_SCSV) && defined(MBEDTLS_SSL_CLI_C)
unsigned int fallback : 1; /*!< is this a fallback? */
uint8_t fallback /*bool*/; /*!< is this a fallback? */
#endif
#if defined(MBEDTLS_SSL_SRV_C)
unsigned int cert_req_ca_list : 1; /*!< enable sending CA list in
uint8_t cert_req_ca_list /*bool*/; /*!< enable sending CA list in
Certificate Request messages? */
#endif
#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
unsigned int ignore_unexpected_cid : 1; /*!< Determines whether DTLS
uint8_t ignore_unexpected_cid /*bool*/; /*!< Determines whether DTLS
* record with unexpected CID
* should lead to failure. */
#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
#if defined(MBEDTLS_SSL_DTLS_SRTP)
unsigned int dtls_srtp_mki_support : 1; /* support having mki_value
in the use_srtp extension */
uint8_t dtls_srtp_mki_support /*bool*/; /*!< support having mki_value
in the use_srtp extension? */
#endif
/*