Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH] powerpc: mpc5200: Remove VLA usage | Date | Mon, 02 Jul 2018 11:33:32 +1000 |
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Kees Cook <keescook@chromium.org> writes:
> On Fri, Jun 29, 2018 at 2:02 PM, Arnd Bergmann <arnd@arndb.de> wrote: >> On Fri, Jun 29, 2018 at 8:53 PM, Kees Cook <keescook@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=qPXydAacU1RqZWA@mail.gmail.com >>> >>> Signed-off-by: Kees Cook <keescook@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
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