Messages in this thread | | | Date | Thu, 22 Sep 2022 16:26:54 -0400 | Subject | Re: [PATCH 0/4] fortify: Use __builtin_dynamic_object_size() when available | From | Siddhesh Poyarekar <> |
| |
On 2022-09-20 15:21, Kees Cook wrote: > Hi, > > This adjusts CONFIG_FORTIFY_SOURCE's coverage to include greater runtime > size checking from GCC and Clang's __builtin_dynamic_object_size(), which > the compilers can track either via code flow or from __alloc_size() hints. >
FTR, I ran a linux build using gcc with allyesconfig and fortify-metrics[1] to get a sense of how much object size coverage would improve with __builtin_dynamic_object_size. With a total of 3,877 __builtin_object_size calls, about 11.37% succeed in getting a result that is not (size_t)-1. If they were replaced by __builtin_dynamic_object_size as this patch proposes, the success rate improves to 16.25%, which is a ~1.4x improvement.
This is a decent improvement by itself but it can be amplified further by adding __attribute__((access (...)))[2] to function prototypes and definitions, especially for functions that take in buffers and their sizes as arguments since __builtin_dynamic_object_size in gcc is capable of recognizing that and using it for object size determination (and hence to fortify calls) within those functions.
Thanks, Sid
[1] https://github.com/siddhesh/fortify-metrics [2] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
| |