On Tue, Feb 23, 2021 at 08:24:26AM +0100, Ahmad Fatoum wrote:
> This ports over Linux commit 3ce120b16cc5 ("kbuild: add
> '-fno-stack-check' to kernel build options"):
>
> Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>
> kbuild: add '-fno-stack-check' to kernel build options
>
> It appears that hardened gentoo enables "-fstack-check" by default for
> gcc.
>
> That doesn't work _at_all_ for the kernel, because the kernel stack
> doesn't act like a user stack at all: it's much smaller, and it doesn't
> auto-expand on use. So the extra "probe one page below the stack" code
> generated by -fstack-check just breaks the kernel in horrible ways,
> causing infinite double faults etc.
>
> [ I have to say, that the particular code gcc generates looks very
> stupid even for user space where it works, but that's a separate
> issue. ]
>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>
> I am porting it, because it may become more acute with the incoming
> support for multiple stacks (via initjmp).
>
> Signed-off-by: Ahmad Fatoum <ahmad@xxxxxx>
> ---
Applied, thanks
Sascha
> Makefile | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/Makefile b/Makefile
> index f3c85cff9430..fa7fbbeb35f0 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -622,6 +622,9 @@ KBUILD_CFLAGS += $(call cc-option, -fno-delete-null-pointer-checks,)
> # disable invalid "can't wrap" optimizations for signed / pointers
> KBUILD_CFLAGS += $(call cc-option,-fno-strict-overflow)
>
> +# Make sure -fstack-check isn't enabled (like gentoo apparently did)
> +KBUILD_CFLAGS += $(call cc-option,-fno-stack-check)
> +
> KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
>
> # Align the bit size of userspace programs with the kernel
> --
> 2.30.0
>
>
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