Re: [PATCH v4 34/75] x86/head/64: Build k/head64.c with -fno-stack-protector

Kees Cook
2020-07-15T01:34:30Z

On Tue, Jul 14, 2020 at 02:08:36PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> The code inserted by the stack protector does not work in the early
> boot environment because it uses the GS segment, at least with memory
> encryption enabled. Make sure the early code is compiled without this
> feature enabled.
>
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
> arch/x86/kernel/Makefile | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index e77261db2391..1b166b866059 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -39,6 +39,10 @@ ifdef CONFIG_FRAME_POINTER
> OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
> endif
>
> +# make sure head64.c is built without stack protector
> +nostackp := $(call cc-option, -fno-stack-protector)
> +CFLAGS_head64.o := $(nostackp)

Recent refactoring[1] for stack protector suggests this should just
unconditionally be:

CFLAGS_head64.o += -fno-stack-protector

But otherwise, yeah, this should be fine here -- it's all early init
stuff.

Reviewed-by: Kees Cook <keescook@chromium.org>

[1] https://lore.kernel.org/lkml/20200626185913.92890-1-masahiroy@kernel.org/

> +
> # If instrumentation of this dir is enabled, boot hangs during first second.
> # Probably could be more selective here, but note that files related to irqs,
> # boot, dumpstack/stacktrace, etc are either non-interesting or can lead to
> --
> 2.27.0
>

--
Kees Cook