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mbedtls/library/mps_reader.c
Hanno Becker ecb02fbbc5 Apply suggestions from code review 
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
2021-03-29 14:20:18 +01:00

565 lines
20 KiB
C
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/*
* Message Processing Stack, Reader implementation
*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may
* not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* This file is part of Mbed TLS (https://tls.mbed.org)
*/
#include "common.h"
#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
#include "mps_reader.h"
#include "mps_common.h"
#include "mps_trace.h"
#include <string.h>
#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
!defined(inline) && !defined(__cplusplus)
#define inline __inline
#endif
#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_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_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_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_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_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_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_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_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_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_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_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_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_comment,
"There has been an unsatisfied read with %u bytes overhead.",
(unsigned) pending );
if( acc == NULL )
{
MBEDTLS_MPS_TRACE( mbedtls_mps_trace_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_error,
"The accumulator is too small to handle the backup." );
MBEDTLS_MPS_TRACE( mbedtls_mps_trace_error,
"* Size: %u", (unsigned) acc_len );
MBEDTLS_MPS_TRACE( mbedtls_mps_trace_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_comment,
"Fragment backup: %u", (unsigned) frag_backup_len );
MBEDTLS_MPS_TRACE( mbedtls_mps_trace_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 uncmmitted 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_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_EXPERIMENTAL */
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