What Happened After Google Retrofitted Memory Safety Onto Its C++ Codebase?

Google's transistion to Safe Coding and memory-safe languages "will take multiple years," according to a post on Google's security blog. So "we're also retrofitting secure-by-design principles to our existing C++ codebase wherever possible," a process which includes "working towards bringing spatial memory safety into as many of our C++ codebases as possible, including Chrome and the monolithic codebase powering our services."


We've begun by enabling hardened libc++, which adds bounds checking to standard C++ data structures, eliminating a significant class of spatial safety bugs. While C++ will not become fully memory-safe, these improvements reduce risk as discussed in more detail in our perspective on memory safety, leading to more reliable and secure software... It's also worth noting that similar hardening is available in other C++ standard libraries, such as libstdc++. Building on the successful deployment of hardened libc++ in Chrome in 2022, we've now made it default across our server-side production systems. This improves spatial memory safety across our services, including key performance-critical components of products like Search, Gmail, Drive, YouTube, and Maps... The performance impact of these changes was surprisingly low, despite Google's modern C++ codebase making heavy use of libc++. Hardening libc++ resulted in an average 0.30% performance impact across our services (yes, only a third of a percent) ...


In just a few months since enabling hardened libc++ by default, we've already seen benefits. Hardened libc++ has already disrupted an internal red team exercise and would have prevented another one that happened before we enabled hardening, demonstrating its effectiveness in thwarting exploits. The safety checks have uncovered over 1,000 bugs, and would prevent 1,000 to 2,000 new bugs yearly at our current rate of C++ development...

The process of identifying and fixing bugs uncovered by hardened libc++ led to a 30% reduction in our baseline segmentation fault rate across production, indicating improved code reliability and quality. Beyond crashes, the checks also caught errors that would have otherwise manifested as unpredictable behavior or data corruption... Hardened libc++ enabled us to identify and fix multiple bugs that had been lurking in our code for more than a decade. The checks transform many difficult-to-diagnose memory corruptions into immediate and easily debuggable errors, saving developers valuable time and effort.

The post notes that they're also working on "making it easier to interoperate with memory-safe languages. Migrating our C++ to Safe Buffers shrinks the gap between the languages, which simplifies interoperability and potentially even an eventual automated translation."

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