analyzer: complain about tainted sizes with "access" attribute [PR103940]

GCC 10 gained the "access" function and type attribute, which
optionally can take a size-index param:
  https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

-fanalyzer in trunk (for GCC 12) has gained a -Wanalyzer-tainted-size to
complain about attacker-controlled size values, but this was only being
used deep inside the region-model code when handling the hardcoded known
behavior of certain functions (memset, IIRC).

This patch extends -Wanalyzer-tainted-size to also complain about
unsanitized attacker-controlled values being passed to function
parameters marked as a size via the "access" attribute.

Note that -fanalyzer-checker=taint is currently required in
addition to -fanalyzer to use this warning, due to scaling issues
(see bug 103533).

gcc/analyzer/ChangeLog:
	PR analyzer/103940
	* engine.cc (impl_sm_context::impl_sm_context): Add
	"unknown_side_effects" param and use it to initialize
	new m_unknown_side_effects field.
	(impl_sm_context::unknown_side_effects_p): New.
	(impl_sm_context::m_unknown_side_effects): New.
	(exploded_node::on_stmt): Pass unknown_side_effects to sm_ctxt
	ctor.
	* sm-taint.cc: Include "stringpool.h" and "attribs.h".
	(tainted_size::tainted_size): Drop "dir" param.
	(tainted_size::get_kind): Drop "FINAL".
	(tainted_size::emit): Likewise.
	(tainted_size::m_dir): Drop unused field.
	(class tainted_access_attrib_size): New subclass.
	(taint_state_machine::on_stmt): Call check_for_tainted_size_arg on
	external functions with unknown side effects.
	(taint_state_machine::check_for_tainted_size_arg): New.
	(region_model::check_region_for_taint): Drop "dir" param from
	tainted_size ctor.
	* sm.h (sm_context::unknown_side_effects_p): New.

gcc/testsuite/ChangeLog:
	PR analyzer/103940
	* gcc.dg/analyzer/taint-size-access-attr-1.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

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