The change that was approved today is a GCC flag change for now using "-fstack-protector-strong" on building Fedora RPM packages rather than just the "-fstack-protector" argument. The -fstack-protector flag has the compiler generate extra code automatically to check for buffer overflows. If a guard check fails -- meaning a potential buffer overflow occurred within the application -- there's an error message and the program exits. Fedora has been using -fstack-protector but now they are looking to use -fstack-protector-strong.
The strong fstack-protector came out of Google and was committed last year to the GNU Compiler Collection. The -fstack-protector-strong is a middle ground between the simple fstack-protector and fstack-protector-all, which is the greatest level of stack protection but can cost in run-time performance. Google suffered from a performance penalty when using fstack-protector-all for Chrome OS, so they devised fstack-protector-strong as a nice balance between the two existing commands.
When it was published last year, Google had been using it with Chromium OS already for a period of two years and didn't find any security problems.
Fedora 20 will now build with fstack-protector-strong to provide for greater stack protection over their simple fstack-protector they had been using, but aren't leaping to fstack-protector-all.
While this has the potential for slightly decreasing the performance, if there are performance regressions to be found, a reversion could take place prior to the mass rebuild for the Fedora 20 release. The details of this change were shared in today's FESCo meeting minutes.