/* * Message Processing Stack, Reader implementation * * Copyright The Mbed TLS Contributors * SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */ #include "common.h" #if defined(MBEDTLS_SSL_PROTO_TLS1_3) #include "mps_reader.h" #include "mps_common.h" #include "mps_trace.h" #include <string.h> #if defined(MBEDTLS_MPS_ENABLE_TRACE) static int mbedtls_mps_trace_id = MBEDTLS_MPS_TRACE_BIT_READER; #endif /* MBEDTLS_MPS_ENABLE_TRACE */ /* * GENERAL NOTE ON CODING STYLE * * The following code intentionally separates memory loads * and stores from other operations (arithmetic or branches). * This leads to the introduction of many local variables * and significantly increases the C-code line count, but * should not increase the size of generated assembly. * * The reason for this is twofold: * (1) It will ease verification efforts using the VST * (Verified Software Toolchain) * whose program logic cannot directly reason * about instructions containing a load or store in * addition to other operations (e.g. *p = *q or * tmp = *p + 42). * (2) Operating on local variables and writing the results * back to the target contexts on success only * allows to maintain structure invariants even * on failure - this in turn has two benefits: * (2.a) If for some reason an error code is not caught * and operation continues, functions are nonetheless * called with sane contexts, reducing the risk * of dangerous behavior. * (2.b) Randomized testing is easier if structures * remain intact even in the face of failing * and/or non-sensical calls. * Moreover, it might even reduce code-size because * the compiler need not write back temporary results * to memory in case of failure. * */ static inline int mps_reader_is_accumulating( mbedtls_mps_reader const *rd) { mbedtls_mps_size_t acc_remaining; if (rd->acc == NULL) { return 0; } acc_remaining = rd->acc_share.acc_remaining; return acc_remaining > 0; } static inline int mps_reader_is_producing( mbedtls_mps_reader const *rd) { unsigned char *frag = rd->frag; return frag == NULL; } static inline int mps_reader_is_consuming( mbedtls_mps_reader const *rd) { return !mps_reader_is_producing(rd); } static inline mbedtls_mps_size_t mps_reader_get_fragment_offset( mbedtls_mps_reader const *rd) { unsigned char *acc = rd->acc; mbedtls_mps_size_t frag_offset; if (acc == NULL) { return 0; } frag_offset = rd->acc_share.frag_offset; return frag_offset; } static inline mbedtls_mps_size_t mps_reader_serving_from_accumulator( mbedtls_mps_reader const *rd) { mbedtls_mps_size_t frag_offset, end; frag_offset = mps_reader_get_fragment_offset(rd); end = rd->end; return end < frag_offset; } static inline void mps_reader_zero(mbedtls_mps_reader *rd) { /* A plain memset() would likely be more efficient, * but the current way of zeroing makes it harder * to overlook fields which should not be zero-initialized. * It's also more suitable for FV efforts since it * doesn't require reasoning about structs being * interpreted as unstructured binary blobs. */ static mbedtls_mps_reader const zero = { .frag = NULL, .frag_len = 0, .commit = 0, .end = 0, .pending = 0, .acc = NULL, .acc_len = 0, .acc_available = 0, .acc_share = { .acc_remaining = 0 } }; *rd = zero; } int mbedtls_mps_reader_init(mbedtls_mps_reader *rd, unsigned char *acc, mbedtls_mps_size_t acc_len) { MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_init"); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "* Accumulator size: %u bytes", (unsigned) acc_len); mps_reader_zero(rd); rd->acc = acc; rd->acc_len = acc_len; MBEDTLS_MPS_TRACE_RETURN(0); } int mbedtls_mps_reader_free(mbedtls_mps_reader *rd) { MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_free"); mps_reader_zero(rd); MBEDTLS_MPS_TRACE_RETURN(0); } int mbedtls_mps_reader_feed(mbedtls_mps_reader *rd, unsigned char *new_frag, mbedtls_mps_size_t new_frag_len) { mbedtls_mps_size_t copy_to_acc; MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_feed"); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "* Fragment length: %u bytes", (unsigned) new_frag_len); if (new_frag == NULL) { MBEDTLS_MPS_TRACE_RETURN(MBEDTLS_ERR_MPS_READER_INVALID_ARG); } MBEDTLS_MPS_STATE_VALIDATE_RAW(mps_reader_is_producing( rd), "mbedtls_mps_reader_feed() requires reader to be in producing mode"); if (mps_reader_is_accumulating(rd)) { unsigned char *acc = rd->acc; mbedtls_mps_size_t acc_remaining = rd->acc_share.acc_remaining; mbedtls_mps_size_t acc_available = rd->acc_available; /* Skip over parts of the accumulator that have already been filled. */ acc += acc_available; copy_to_acc = acc_remaining; if (copy_to_acc > new_frag_len) { copy_to_acc = new_frag_len; } /* Copy new contents to accumulator. */ memcpy(acc, new_frag, copy_to_acc); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Copy new data of size %u of %u into accumulator at offset %u", (unsigned) copy_to_acc, (unsigned) new_frag_len, (unsigned) acc_available); /* Check if, with the new fragment, we have enough data. */ acc_remaining -= copy_to_acc; if (acc_remaining > 0) { /* We need to accumulate more data. Stay in producing mode. */ acc_available += copy_to_acc; rd->acc_share.acc_remaining = acc_remaining; rd->acc_available = acc_available; MBEDTLS_MPS_TRACE_RETURN(MBEDTLS_ERR_MPS_READER_NEED_MORE); } /* We have filled the accumulator: Move to consuming mode. */ MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Enough data available to serve user request"); /* Remember overlap of accumulator and fragment. */ rd->acc_share.frag_offset = acc_available; acc_available += copy_to_acc; rd->acc_available = acc_available; } else { /* Not accumulating */ rd->acc_share.frag_offset = 0; } rd->frag = new_frag; rd->frag_len = new_frag_len; rd->commit = 0; rd->end = 0; MBEDTLS_MPS_TRACE_RETURN(0); } int mbedtls_mps_reader_get(mbedtls_mps_reader *rd, mbedtls_mps_size_t desired, unsigned char **buffer, mbedtls_mps_size_t *buflen) { unsigned char *frag; mbedtls_mps_size_t frag_len, frag_offset, end, frag_fetched, frag_remaining; MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_get"); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "* Bytes requested: %u", (unsigned) desired); MBEDTLS_MPS_STATE_VALIDATE_RAW(mps_reader_is_consuming( rd), "mbedtls_mps_reader_get() requires reader to be in consuming mode"); end = rd->end; frag_offset = mps_reader_get_fragment_offset(rd); /* Check if we're still serving from the accumulator. */ if (mps_reader_serving_from_accumulator(rd)) { /* Illustration of supported and unsupported cases: * * - Allowed #1 * * +-----------------------------------+ * | frag | * +-----------------------------------+ * * end end+desired * | | * +-----v-------v-------------+ * | acc | * +---------------------------+ * | | * frag_offset acc_available * * - Allowed #2 * * +-----------------------------------+ * | frag | * +-----------------------------------+ * * end end+desired * | | * +----------v----------------v * | acc | * +---------------------------+ * | | * frag_offset acc_available * * - Not allowed #1 (could be served, but we don't actually use it): * * +-----------------------------------+ * | frag | * +-----------------------------------+ * * end end+desired * | | * +------v-------------v------+ * | acc | * +---------------------------+ * | | * frag_offset acc_available * * * - Not allowed #2 (can't be served with a contiguous buffer): * * +-----------------------------------+ * | frag | * +-----------------------------------+ * * end end + desired * | | * +------v--------------------+ v * | acc | * +---------------------------+ * | | * frag_offset acc_available * * In case of Allowed #2 we're switching to serve from * `frag` starting from the next call to mbedtls_mps_reader_get(). */ unsigned char *acc; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Serve the request from the accumulator"); if (frag_offset - end < desired) { mbedtls_mps_size_t acc_available; acc_available = rd->acc_available; if (acc_available - end != desired) { /* It might be possible to serve some of these situations by * making additional space in the accumulator, removing those * parts that have already been committed. * On the other hand, this brings additional complexity and * enlarges the code size, while there doesn't seem to be a use * case where we don't attempt exactly the same `get` calls when * resuming on a reader than what we tried before pausing it. * If we believe we adhere to this restricted usage throughout * the library, this check is a good opportunity to * validate this. */ MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS); } } acc = rd->acc; acc += end; *buffer = acc; if (buflen != NULL) { *buflen = desired; } end += desired; rd->end = end; rd->pending = 0; MBEDTLS_MPS_TRACE_RETURN(0); } /* Attempt to serve the request from the current fragment */ MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Serve the request from the current fragment."); frag_len = rd->frag_len; frag_fetched = end - frag_offset; /* The amount of data from the current * fragment that has already been passed * to the user. */ frag_remaining = frag_len - frag_fetched; /* Remaining data in fragment */ /* Check if we can serve the read request from the fragment. */ if (frag_remaining < desired) { MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "There's not enough data in the current fragment " "to serve the request."); /* There's not enough data in the current fragment, * so either just RETURN what we have or fail. */ if (buflen == NULL) { if (frag_remaining > 0) { rd->pending = desired - frag_remaining; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Remember to collect %u bytes before re-opening", (unsigned) rd->pending); } MBEDTLS_MPS_TRACE_RETURN(MBEDTLS_ERR_MPS_READER_OUT_OF_DATA); } desired = frag_remaining; } /* There's enough data in the current fragment to serve the * (potentially modified) read request. */ frag = rd->frag; frag += frag_fetched; *buffer = frag; if (buflen != NULL) { *buflen = desired; } end += desired; rd->end = end; rd->pending = 0; MBEDTLS_MPS_TRACE_RETURN(0); } int mbedtls_mps_reader_commit(mbedtls_mps_reader *rd) { mbedtls_mps_size_t end; MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_commit"); MBEDTLS_MPS_STATE_VALIDATE_RAW(mps_reader_is_consuming( rd), "mbedtls_mps_reader_commit() requires reader to be in consuming mode"); end = rd->end; rd->commit = end; MBEDTLS_MPS_TRACE_RETURN(0); } int mbedtls_mps_reader_reclaim(mbedtls_mps_reader *rd, int *paused) { unsigned char *frag, *acc; mbedtls_mps_size_t pending, commit; mbedtls_mps_size_t acc_len, frag_offset, frag_len; MBEDTLS_MPS_TRACE_INIT("mbedtls_mps_reader_reclaim"); if (paused != NULL) { *paused = 0; } MBEDTLS_MPS_STATE_VALIDATE_RAW(mps_reader_is_consuming( rd), "mbedtls_mps_reader_reclaim() requires reader to be in consuming mode"); frag = rd->frag; acc = rd->acc; pending = rd->pending; commit = rd->commit; frag_len = rd->frag_len; frag_offset = mps_reader_get_fragment_offset(rd); if (pending == 0) { MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "No unsatisfied read-request has been logged."); /* Check if there's data left to be consumed. */ if (commit < frag_offset || commit - frag_offset < frag_len) { MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "There is data left to be consumed."); rd->end = commit; MBEDTLS_MPS_TRACE_RETURN(MBEDTLS_ERR_MPS_READER_DATA_LEFT); } rd->acc_available = 0; rd->acc_share.acc_remaining = 0; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Fragment has been fully processed and committed."); } else { int overflow; mbedtls_mps_size_t acc_backup_offset; mbedtls_mps_size_t acc_backup_len; mbedtls_mps_size_t frag_backup_offset; mbedtls_mps_size_t frag_backup_len; mbedtls_mps_size_t backup_len; mbedtls_mps_size_t acc_len_needed; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "There has been an unsatisfied read with %u bytes overhead.", (unsigned) pending); if (acc == NULL) { MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "No accumulator present"); MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_NEED_ACCUMULATOR); } acc_len = rd->acc_len; /* Check if the upper layer has already fetched * and committed the contents of the accumulator. */ if (commit < frag_offset) { /* No, accumulator is still being processed. */ frag_backup_offset = 0; frag_backup_len = frag_len; acc_backup_offset = commit; acc_backup_len = frag_offset - commit; } else { /* Yes, the accumulator is already processed. */ frag_backup_offset = commit - frag_offset; frag_backup_len = frag_len - frag_backup_offset; acc_backup_offset = 0; acc_backup_len = 0; } backup_len = acc_backup_len + frag_backup_len; acc_len_needed = backup_len + pending; overflow = 0; overflow |= (backup_len < acc_backup_len); overflow |= (acc_len_needed < backup_len); if (overflow || acc_len < acc_len_needed) { /* Except for the different return code, we behave as if * there hadn't been a call to mbedtls_mps_reader_get() * since the last commit. */ rd->end = commit; rd->pending = 0; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_ERROR, "The accumulator is too small to handle the backup."); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_ERROR, "* Size: %u", (unsigned) acc_len); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_ERROR, "* Needed: %u (%u + %u)", (unsigned) acc_len_needed, (unsigned) backup_len, (unsigned) pending); MBEDTLS_MPS_TRACE_RETURN( MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL); } MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Fragment backup: %u", (unsigned) frag_backup_len); MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Accumulator backup: %u", (unsigned) acc_backup_len); /* Move uncommitted parts from the accumulator to the front * of the accumulator. */ memmove(acc, acc + acc_backup_offset, acc_backup_len); /* Copy uncommitted parts of the current fragment to the * accumulator. */ memcpy(acc + acc_backup_len, frag + frag_backup_offset, frag_backup_len); rd->acc_available = backup_len; rd->acc_share.acc_remaining = pending; if (paused != NULL) { *paused = 1; } } rd->frag = NULL; rd->frag_len = 0; rd->commit = 0; rd->end = 0; rd->pending = 0; MBEDTLS_MPS_TRACE(MBEDTLS_MPS_TRACE_TYPE_COMMENT, "Final state: aa %u, al %u, ar %u", (unsigned) rd->acc_available, (unsigned) rd->acc_len, (unsigned) rd->acc_share.acc_remaining); MBEDTLS_MPS_TRACE_RETURN(0); } #endif /* MBEDTLS_SSL_PROTO_TLS1_3 */
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