Exciting to see this in the standard. Once this is in all compilers, this will probably have security effects beyond C.
Fun fact: Miguel Ojeda linked to @cperciva's article and its following HN discussion in the note (N2897) to propose this: https://news.ycombinator.com/item?id=8270136
memset_explicit is just to overcome stubborn optimizer people who insist to optimize functions away (without warnings!), even when they have no idea about side-effects.
Wow, was that a requirement for memset_s? I'd never heard of timing being a something guaranteed by the *_s functions, regardless of security being in their name.
(if it isn't, hopefully somebody who knows more will post a better link)
Up until now, safely implementing explicit_bzero() has depended on various hacks that a new compiler version might drag out from under you. This should end the "arms race".
Had a disscussion about this here:
I tried the following code in a few compilers, it works perfectly for overwriting buffer pointers that goes out of scope, also tested removing the volatile to ensure that the memory write was ignored and I reproduced the code vulnerability where the previous message was still there the second time I tried to read a message, and from the way I read the spec this shouldn't be optimized away by any compiler:
void memset_explicit(char* p, char c, size_t n) {
volatile char* vp = p;
while (n--) *vp++ = c;
}