Clear some confusion between `X` as the output variable and "X" as a name
given to the accumulator. Previous iterations of the code used the variable
`X` as the accumulator, but now that the accumulator is `W[x_index]`, some
of the comments didn't make sense.
Remove the copy of the initial value of `X` into `W[x_index]`, which was
meaningless: the initial value of an output variable should not, and did
not, matter. `W[x_index]` is later overridden unconditionally to take the
value `RR`.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Reduce the size of mbedtls_mpi from 3 words to 2 on most architectures.
This also reduces the code size significantly in bignum.o and ecp_curves.o,
with negligible variations in other modules.
This removes the ability to set MBEDTLS_MPI_MAX_LIMBS to a value >=65536,
but we don't support customizing this value anyway (it's always 10000).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
IAR was warning that conditional execution could bypass initialisation of
variables, although those same variables were not used uninitialised.
Signed-off-by: Paul Elliott <paul.elliott@arm.com>
In some contexts, the output pointer may equal the first input
pointer, in which case copying is not only superfluous but results in
"Source and destination overlap in memcpy" errors from Valgrind (as I
observed in the context of ecp_double_jac) and a diagnostic message
from TrustInSoft Analyzer (as Pascal Cuoq reported in the context of
other ECP functions called by cert-app with a suitable certificate).
Signed-off-by: Aaron M. Ucko <ucko@ncbi.nlm.nih.gov>
Shuffle things around a bit inside mbedtls_mpi_random() in preparation for
breaking out mbedtls_mpi_core_random().
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Rewrite the minimum bound comparison to avoid a local allocation. This costs
a bit of code size, but saves RAM. This is in preparation for moving the
bulk of the function to the bignum_core module where allocation is not
permitted.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
The first half of the table is not used, let's reuse index 0 for the
result instead of appending it in the end.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The table size was set before the configured window size bound was
applied which lead to out of bounds access when the configured window
size bound is less.
Signed-off-by: Janos Follath <janos.follath@arm.com>
The window size starts giving diminishing returns around 6 on most
platforms and highly unlikely to be more than 31 in practical use cases.
Still, compilers and static analysers might complain about this and
better to be pedantic.
Co-authored-by: Gilles Peskine <gilles.peskine@arm.com>
Signed-off-by: Janos Follath <janos.follath@arm.com>
