Re: Adding memset_s function

[Alan Barrett <apb%cequrux.com@localhost>]

On Fri, 24 Feb 2012, Alan Barrett wrote:
> For some time now, I have wanted a function to zero a block of memory, 
> with a guarantee that the compiler will not optimise it away and do 
> nothing.

Regardless of whether or not we add memset_s, perhaps we should 
add something like this to libc:

        /*
         * memset_volatile is a volatile pointer to the memset function.
         * You can call (*memset_volatile)(buf, val, len) or even
         * memset_volatile(buf, val, len) just as you would call
         * memset(buf, val, len), but the use of a volatile pointer
         * guarantees that the compiler will not optimise the call away.
         */
        void * (* volatile memset_volatile)(void *, int, size_t) = memset;

There are several places where we use memset(buf, 0, len) to clear 
a buffer that contains sensitive information (e.g. a password, or 
crypto key), and changing them to use memset_volatile(buf, 0, len) 
instead would ensure that the compiler does not optimise the calls 
away.

--apb (Alan Barrett)