On CHERI, and thus Arm's Morello prototype, pointers are represented as
hardware capabilities, which consist of both an integer address and
additional metadata, meaning they are twice the size of the platform's
size_t type, i.e. 16 bytes on a 64-bit system. The ovector member of
heapframe happens to only be 8 byte aligned, and so computing frame_size
ends up with a multiple of 8 but not 16. Whilst the first frame is
always suitably aligned, this then misaligns the frame that follows it,
resulting in an alignment fault when storing a pointer to Fecode at the
start of match.
Thus, round up frame_size to a multiple of heapframe's alignment to
ensure alignment is preserved. This can be completely optimised away on
traditional architectures and, since CHERI's capabilities are in fact
2 * sizeof(PCRE2_SIZE) bytes in size, the variable part of the
expression is also proven to be a multiple of the alignment and so the
aligning gets folded into the offsetof part by adding an additional 8,
so no dynamic alignment code is needed even on CHERI architectures.
* pcre2_match: avoid crash if subject NULL and PCRE2_ZERO_TERMINATED
When length of subject is PCRE2_ZERO_TERMINATED strlen is used
to calculate its size, which will trigger a crash if subject is
also NULL.
Move the NULL check before strlen on it would be used, and make
sure or dependent variables are set after the NULL validation
as well.
While at it, fix a typo in a debug flag in the same file, which
is otherwise unrelated and make sure the full section of constrain
checks can be identified clearly using the leading comment alone.
* pcre2_dfa_match: avoid crash if subject NULL and PCRE2_ZERO_TERMINATED
When length of subject is PCRE2_ZERO_TERMINATED strlen is used
to calculate its size, which will trigger a crash if subject is
also NULL.
Move the NULL check before the detection for subject sizes to
avoid this issue.
* pcre2_substitute: avoid crash if subject or replacement are NULL
The underlying pcre2_match() function will validate the subject if
needed, but will crash when length is PCRE2_ZERO_TERMINATED or if
subject == NULL and pcre2_match() is not being called because
match_data was provided.
The replacement parameter is missing NULL checks, and so currently
allows for an equivalent response to "" if rlength == 0.
Restrict all other cases to avoid strlen(NULL) crashes in the same
way that is done for subject, but also make sure to reject invalid
length values as early as possible.
Zoltan Herczeg
Philip Hazel
Jessica Clarke
Carlo Marcelo Arenas Belón