Kees Cook <keesc...@chromium.org> writes: > On Fri, Jun 29, 2018 at 2:02 PM, Arnd Bergmann <a...@arndb.de> wrote: >> On Fri, Jun 29, 2018 at 8:53 PM, Kees Cook <keesc...@chromium.org> wrote: >>> In the quest to remove all stack VLA usage from the kernel[1], this >>> switches to using a stack size large enough for the saved routine and >>> adds a sanity check. >>> >>> [1] >>> https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qpxydaacu1rq...@mail.gmail.com >>> >>> Signed-off-by: Kees Cook <keesc...@chromium.org> >> >> This seems particularly nice, not only avoids it the dynamic stack >> allocation, it >> also makes sure the new 0x500 handler doesn't overflow into the 0x600 >> exception handler. >> >> It would help to explain how you arrived at that '256 byte' number in >> the changelog though. > > Honestly, I just counted instructions, multiplied by 8 and rounded up > to the next nearest power of 2, and the result felt right for giving > some level of flexibility for code growth before tripping the WARN. :P > > I'm happy to adjust, of course. :)
What if we write it: char saved_0x500[0x600 - 0x500]; Hopefully the compiler is smart enough not to generate a VLA for that :) cheers