Fix undefined behavior in bignum: NULL+0 and -most-negative-sint #6609
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Since they're part of the public API (even if only through a few functions), they should be documented. I deliberately skipped documenting how to configure the size of the type. Right now, MBEDTLS_HAVE_INT32 and MBEDTLS_HAVE_INT64 have no Doxygen documentation, so it's ambiguous whether they're part of the public API. Resolving this ambiguity is out of scope of my current work. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Fix undefined behavior (typically harmless in practice) of mbedtls_mpi_add_mpi(), mbedtls_mpi_add_abs() and mbedtls_mpi_add_int() when both operands are 0 and the left operand is represented with 0 limbs. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
When x is the most negative value of a two's complement type, `(unsigned_type)(-x)` has undefined behavior, whereas `-(unsigned_type)x` has well-defined behavior and does what was intended. Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
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@daverodgman @tom-cosgrove-arm This is a subset of #6614 which you've approved. I'll make a backport ASAP |
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Backport is up: #6618 |
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Fix two kinds of typically harmless undefined behavior in bignum:
mbedtls_mpi_add_abs()A reasonably modern UBSan with Clang (Ubuntu 20.04 with Clang 10) complains about both (but not GCC 12 from Ubuntu 22.04 or Clang 6 from Ubuntu 18.04). The addition bug already had a test, but we only run an ancient UBSan on our CI. I added a test for -SINT_MIN, without using the test framework to pass function arguments because you can't easily pass the interesting values.
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