Fortify metrics

This project is a couple of tools that does source or binary analysis to get an estimate of how much of a program or project is fortified as a result of building with the _FORTIFY_SOURCE macro.

fmetrics GCC plugin

This plugin helps get source level statistics on object size computation in source code. Specifically, when a source file is built with this plugin invoked, it will print the number of times that the __builtin_object_size builtin was computed successfully along with the number of times it would have been computed successfully if it were replaced with __builtin_dynamic_object_size.

Building

make to build and make check to run tests.

Running

Add -fplugin=$PATH_TO/fmetrics.so -fplugin-arg-fmetrics-project=SOMENAME to CFLAGS or CXXFLAGS of the project you intend to analyze and then build it. The output for every source file is written out to stderr in the form:

SOMENAME:: TOTAL:BOS:BDOS

Where SOMENAME is what you passed in the CFLAGS above, TOTAL is the number of __builtin_object_size encountered, BOS is the number of __builtin_object_size that the compiler successfully resolved to something other than (size_t) -1 and BDOS is the corresponding success count if the builtin were replaced with __builtin_dynamic_object_size.

Known limitations of fmetrics.so

The __builtin_object_size builtin may get folded away early in some cases, thus eluding the plugin. These cases however are successes or failures (e.g. in handling of volatile expressions) in both __builtin_object_size and __builtin_dynamic_object_size, so the meaning of the metrics should not change. The percentage changes however may look different from the ideal case.

fortify-metrics.py

Parse DSOs to get statistics for how well _FORTIFY_SOURCE did with that DSO. This is different from OpenOSC, which aims to be more precise at compile time and add instrumentation for enhanced diagnostics. This project aims to do none of that and as a result, can be deployed pretty much anywhere and just pointed at a path or a DSO. Further, OpenOSC assumes constant object sizes, which makes it unsuitable for _FORTIFY_SOURCE=3.

usage: fortify-metrics.py [-h] [-v] [-l] [-f] path [path ...]

Get build time statistics of _FORTIFY_SOURCE coverage for ELF files in given
directories.

positional arguments:
  path            Files or directories to analyze

optional arguments:
  -h, --help      show this help message and exit
  -v, --verbose   Verbose mode.
  -l, --listall   Include fortifiable functions with zero call counts.
  -f, --fullpath  Show full path in binary names.

Known Limitations of fortify-metrics.py

More _chk function calls does not necessarily mean better fortification because calls may have been simplified to their regular variants and in some cases, inlined or transformed to simpler calls. One could make reasonable conclusions from the data though, based on changes in total calls across all fortifiable functions.

Contributing

Submit a pull request or file an issue!