[PATCH] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

[Nathan Chancellor]

On Fri, Mar 07, 2025 at 02:57:06PM -0800, Kees Cook wrote:
> 
> 
> On March 7, 2025 1:47:34 PM PST, Nathan Chancellor <nathan at kernel.org> wrote:
> >On Tue, Mar 04, 2025 at 09:50:44AM -0800, Kees Cook wrote:
> >> On Mon, 03 Mar 2025 13:49:37 -0800, Kees Cook wrote:
> >> > The i386 regparm bug exposed with FORTIFY_SOURCE with Clang was fixed
> >> > in Clang 16[1].
> >> > 
> >> > 
> >> 
> >> Applied to for-next/hardening, thanks!
> >> 
> >> [1/1] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+
> >>       https://git.kernel.org/kees/c/3e5820429980
> >
> >Turns out this is actually incomplete based on my testing, I see the
> >following warnings with ARCH=i386 allmodconfig with all supported clang
> >versions:
> >
> >  warning: unsafe strcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strcpy-lit.c
> >  warning: unsafe strcpy() usage lacked '__write_overflow' symbol in lib/test_fortify/write_overflow-strcpy.c
> >
> >We also need to drop '-ffreestanding' from arch/x86/Makefile (which Nick
> >has mentioned in [1]). Time to revive [2]? :) or just do it in this
> >patch, since it sounds like there was no regression with GCC?
> >
> >[1]: https://github.com/ClangBuiltLinux/linux/issues/1583#issuecomment-1123016466
> >[2]: https://lore.kernel.org/20200817220212.338670-5-ndesaulniers@google.com/
> 
> Oh good catch! Probably I need to do this in two patches just to be safe:
> - make -ffreestanding be Clang only
> - switch to version checks for FORTIFY and freestanding
> 
> That will split the changes for GCC and Clang into separate patches. Or maybe that's overkill?

No, I think that is reasonable, as any regressions with GCC would be
noticed by the first change, rather than being mixed in with the second.
It should also make it easier to drop that when the minimum version of
clang gets bumped to 16 (either for the whole kernel or just x86, like
the bump to 15 this dev cycle for the recent stack protector fixes in
-top).

Cheers,
Nathan