On Fri, Mar 02, 2018 at 08:50:17PM +0100, Jason A. Donenfeld wrote: [..] > What would be really nice would be to somehow keep track of the > maximum stack depth, and just before the function returns, clear from > the maximum depth to its stack base, all in one single call. This > would not only make the code faster and less brittle, but it would > also clean up some algorithms quite a bit. > > Ideally this would take the form of a gcc attribute on the function, > but I was unable to find anything of that nature. I started looking > for little C tricks for this, and came up dry too. I realize I could > probably just take the current stack address and zero out until _the > very end_ but that seems to overshoot and would probably be bad for > performance. The best I've been able to do come up with are some > x86-specific macros, but that approach seems a bit underwhelming. > Other approaches include adding a new attribute via the gcc plugin > system, which could make this kind of thing more complete [cc'ing > pipacs in case he's thought about that before].
Can objtool support a static stack usage analysis? I'm wondering if it's possible to place these sensitive functions in a special linker section, like .text.stackzero.<tag>; objtool could collect static call data (as it already does) and stack usage, spitting out a symbol definition stackzero_<tag>_max_depth, which you could then use to bound your zeroing. Obviously this is a static analysis, with the limitations therein. Julia
