From 168ac780349dd04dcd552a2bbf24dfe164b0e901 Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Thu, 26 Feb 2026 11:44:02 +0100 Subject: [PATCH] Be more specific about what compiler options we consider legitimate Signed-off-by: Gilles Peskine --- SECURITY.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/SECURITY.md b/SECURITY.md index ebb53e9962..edd0a115c3 100644 --- a/SECURITY.md +++ b/SECURITY.md @@ -108,7 +108,7 @@ model, they need to be mitigated by physical countermeasures. Mbed TLS is mostly written in C. We use standard C except with known compilers, so we do not expect compilers to introduce direct vulnerabilities. However, compilers can introduce [timing side channels](#timing-attacks) in code that was intended to be constant-time. Mbed TLS includes countermeasures to try to prevent this. But given the diversity of compilers, compiler options and target platforms, this prevention may not be complete. -We recommend compiling Mbed TLS with commonly used levels of optimizations, such as `-O2` or `-Os`. Higher levels of optimization such as `-O3` or `-Oz` are likely to be safe but are less scrutinized. We do not recommend using less vetted optimization options unless your system is physically isolated. +We recommend compiling Mbed TLS with commonly used levels of optimizations, such as `-O2` or `-Os`. We will generally treat exploitable timing side channels as a vulnerability if they appear with a common compiler at a common level of optimization. Higher levels of optimization such as `-O3` or `-Oz` are still likely to be safe but are less scrutinized. We do not recommend using individual options that might introduce data-dependent timing, and we will not try to work around such optimizations if they are not part of a commonly used level. #### Out-of-scope countermeasures