Re: [PATCH v3 35/75] x86/head/64: Build k/head64.c with -fno-stack-protector

Brian Gerst
2020-05-19T13:58:18Z

On Tue, Apr 28, 2020 at 11:28 AM Joerg Roedel <joro@8bytes.org> 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 ba89cabe5fcf..1192de38fa56 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -35,6 +35,10 @@ 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)
> +
> # 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

The proper fix would be to initialize MSR_GS_BASE earlier.

--
Brian Gerst