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Overeager Compilers Can Open Security Holes In Your Code
jfruh writes: "Creators of compilers are in an arms race to improve performance. But according to a presentation at this week's annual USENIX conference, those performance boosts can undermine your code's security. For instance, a compiler might find a subroutine that checks a huge bound of memory beyond what's allocated to the program, decide it's an error, and eliminate it from the compiled machine code — even though it's a necessary defense against buffer overflow attacks."
This is just as poorly written up as last time. These are truly bugs in the programs using undefined parts of the language. It's silly to blame the compiler.
This is not really about the existence of bad compiler optimization - it is about a tool called Stack that can be used to detect this, which is known as "unstable" code, and has been used to find lots of vulnerabilities already.
I know that at least GCC will get rid of overflow checks if they rely on checking the value after overflow (without any warning), because C defines that overflow on signed integers is undefined. This is even documented. If anything is declared by the language specification as being undefined, expect trouble.
Compilers can also "optimize" away Kahan summation algorithm. See page 6 of How Futile are Mindless Assessments of Roundoff in Floating-Point Computation
Except not, so now we have explicit_bzero()