Messages in this thread | | | Date | Tue, 26 Nov 2013 12:19:08 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] use -fstack-protector-strong |
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* Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> On Mon, 25 Nov 2013, Kees Cook wrote: > > > On Mon, Nov 25, 2013 at 3:16 PM, H. Peter Anvin <hpa@zytor.com> wrote: > > > On 11/25/2013 02:14 PM, Kees Cook wrote: > > >> Build the kernel with -fstack-protector-strong when it is available > > >> (gcc 4.9 and later). This increases the coverage of the stack protector > > >> without the heavy performance hit of -fstack-protector-all. > > > > > > What is the difference between the various options? > > > > -fstack-protector-all: > > Adds the stack-canary saving prefix and stack-canary checking suffix > > to _all_ function entry and exit. Results in substantial use of stack > > space for saving the canary for deep stack users (e.g. historically > > xfs), and measurable (though shockingly still low) performance hit due > > to all the saving/checking. Really not suitable for sane systems, and > > was entirely removed as an option from the kernel many years ago. > > > > -fstack-protector: > > Adds the canary save/check to functions that define an 8 > > (--param=ssp-buffer-size=N, N=8 by default) or more byte local char > > array. Traditionally, stack overflows happened with string-based > > manipulations, so this was a way to find those functions. Very few > > total functions actually get the canary; no measurable performance or > > size overhead. > > > > -fstack-protector-strong > > Adds the canary for a wider set of functions, since it's not just > > those with strings that have ultimately been vulnerable to > > stack-busting. With this superset, more functions end up with a > > canary, but it still remains small compared to all functions with no > > measurable change in performance. Based on the original design > > document, a function gets the canary when it contains any of: > > - local variable's address used as part of the RHS of an assignment or > > function argument > > - local variable is an array (or union containing an array), > > regardless of array type or length > > - uses register local variables > > https://docs.google.com/a/google.com/document/d/1xXBH6rRZue4f296vGt9YQcuLVQHeE516stHwt8M9xyU > > > > Chrome OS has been using -fstack-protector-strong for its kernel > > builds for the last 8 months with no problems. > > Could you get this information inside the commit log for your patch > please? This is very valuable info to have right next to the change > in the repository without having to dig into the gcc manual or > finding the relevant email thread.
Another piece of information we need for the changelog is a vmlinux kernel size comparison, with/without the patch, for a defconfig build (or a Ubuntu distro config build).
Thanks,
Ingo
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