Fix the subtraction in fix_negative, which was incorrectly not looking
for a carry. This caused the result to be wrong when the least
significant limb of N was 0. Fix#4296.
The bug was introduced by d10e8fae9e
"Optimize fix_negative". Thanks to Philippe Antoine (catenacyber) for
reporting the bug which was found by his EC differential fuzzer.
Credit to OSS-Fuzz.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This header file will contain declarations of functions that are not
part of the public ABI/API, and must not be called from other modules,
but can be called from unit tests.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Move the handling of the sign out of the base-specific loops. This
both simplifies the code, and corrects an edge case: the code in the
non-hexadecimal case depended on mbedtls_mpi_mul_int() preserving the
sign bit when multiplying a "negative zero" MPI by an integer, which
used to be the case but stopped with PR #2512.
Fix#4295. Thanks to Guido Vranken for analyzing the cause of the bug.
Credit to OSS-Fuzz.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This check was added earlier to avoid useless calls to `memcpy()`
with length `0` in the _frequent_ case where we're not accumulating.
By now, the whole code path has been moved to a branch which is only
executed if the reader is accumulating, and the only time this check
would be relevant is if we happen to feed an empty fragment to the
reader. In this case, the call to memcpy() could be removed, but
since this case is exceptional and the call to memcpy() is still
correct even for a length 0 copy, we remove the check for simplicity
of the code.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Previously, the semantics of mbedtls_mps_reader_commit() was to invalidate
all buffers previously fetched via mbedtls_mps_reader_get(), forbidding
any further use by the 'consumer'. This was in fact a necessary constraint
for the current implementation, which did some memory moving in
mbedtls_mps_reader_commit().
This commit simplifies the reader's semantics and implementation in
the following way:
- API: A call to mbedtls_mps_reader_commit() does no longer invalidate
the buffers previously obtained via mbedtls_mps_reader_get().
Instead, they can continue to be used until
mbedtls_mps_reader_reclaim() is called.
Calling mbedtls_mps_reader_commit() now only sets a marker
indicating which parts of the data received through
mbedtls_mps_reader_get() need not be backed up once
mbedtls_mps_reader_reclaim() is called. Allowing the user
to call mbedtls_mbedtls_reader_commit() multiple times
before mbedtls_mps_reader_reclaim() is mere convenience:
We'd get exactly the same functionality if instead of
mbedtls_mps_reader_commit(), there was an additional argument
to mbedtls_mps_reader_reclaim() indicating how much data
to retain. However, the present design is more convenient
for the user and doesn't appear to introduce any unnecessary
complexity (anymore), so we stick with it for now.
- Implementation: mbedtls_mps_reader_commit() is now a 1-liner,
setting the 'commit-marker', but doing nothing else.
Instead, the complexity of mbedtls_mp_reader_reclaim()
slightly increases because it has to deal with creating
backups from both the accumulator and the current
fragment. In the previous implementation, which shifted
the accumulator content with every call to
mbedtls_mps_reader_commit(), only the backup from the
fragment was necessary; with the new implementation
which doesn't shift anything in
mbedtls_mps_reader_commit(), we need to do the
accumulator shift in mbedtls_mps_reader_reclaim().
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit adds an implementation of the MPS trace module
based on `printf()`.
The enabling macro MBEDTLS_MPS_TRACE remains unset by default
because MPS tracing is very verbose and consumes unnecessary
space in the CI.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit adds an internal header `library/mps/error.h` related
to error codes in MPS.
For now, those error codes can be considered internal and thus we
don't have to avoid clashes with other Mbed TLS error codes. This
is OK as long as it's true that MPS isn't public API, and its error
codes are never forwarded to the return values of public API calls.
The error code allocation of MPS will likely need revisiting over time.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
Most buffers that MPS deals with are small and representable
with integer types of width 16-bit or more.
For highly memory constrained systems, it is therefore a potential
for significant memory savings to use 16-bit types for buffer sizes
throughout MPS.
In prepraration for this, this commit introduces typdefs
```
mbedtls_mps_size_t
mbedtls_mps_stored_size_t
```
for buffer sizes in the MPS implementation and the MPS structures,
respectively.
So far, those MUST be defined as `size_t`: While an effort has been made
to write most of MPS code in terms of `mbedtls_mps_[stored_]size_t` in a
way that would allow narrower types, those aren't yet supported. Still,
we retain the typedefs in order to avoid unnecessary rewriting of a large
body of the MPS codebase.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit adds the interface fo the MPS reader component as
`library/mps/reader.h`.
Please see the file itself for extensive documentation.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
MPS' tracing module uses four macros:
1) TRACE( type, fmt, ... )
This acts like `printf( fmt, ... )` but also allows
the specification of a type of trace output (comment,
warning, error, ...)
2) TRACE_INIT
This acts like TRACE() but increases the level of
indentation. It will be used at the beginning of
function calls.
3) RETURN( val )
Equivalent to `return( val )` plus a decrement in the
level of indentation. This should be used at the end of
functions that have been started with TRACE_INIT.
4) TRACE_END
This combines a trace output with a decrement of the
level of indentation. It's necessary prior to leaving
functions which have been started with TRACE_INIT
but which don't have a return value.
This commit defines those macros as no-op dummies in
`library/mps/trace.h` for now.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit adds an MPS-specific compile-time option
`MBEDTLS_MPS_TRACE` to the internal MPS header `mps/common.h`.
So far -- this may need revisiting -- MPS comes with its own
internal tracing module which allows to track the operation of
MPS' various layers for the purpose of understanding of it workings
as well as for debugging.
The reasons for the introduction of a module separate from SSL debug
are the following:
1) The SSL debug module requires an SSL context to function because
debug callbacks are part of the runtime configuration of the SSL
module.
The MPS tracing module, in contrast, is not supposed to be used
in production environments, and there is no need for a runtime
configuration. Instead, a compile-time defined tracing callback
is used.
2) In the interest of modularity, MPS' tracing module shouldn't
require having an SSL context around.
3) Purely visually, MPS' tracing module adds support for indentation
according to call-depth and coloring according to which module is
being used, which makes it very useful for what's going on; however,
those features aren't available in the SSL debug module (and they
shouldn't be).
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit adds the compile-time option MBEDTLS_MPS_ENABLE_ASSERTIONS
which controls the presence of runtime assertions in MPS code.
See the documentation in the header for more information.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
This commit introduces the internal MPS header `mps/common.h`
which will subsequently be populated with MPS-specific compile-time
options and helper macros. For now, it's a stub.
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
