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From:   Brian Gerst <brgerst@gmail.com>
Date:   Tue, 19 May 2020 09:58:18 -0400
Message-ID: <CAMzpN2gfiBAeCV_1+9ogh42bMMuDW=qdwd7dYp49-=zY3kzBaA@mail.gmail.com>
Subject: Re: [PATCH v3 35/75] x86/head/64: Build k/head64.c with -fno-stack-protector
To:     Joerg Roedel <joro@8bytes.org>
Cc:     "the arch/x86 maintainers" <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Hellstrom <thellstrom@vmware.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        David Rientjes <rientjes@google.com>,
        Cfir Cohen <cfir@google.com>,
        Erdem Aktas <erdemaktas@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mike Stunes <mstunes@vmware.com>,
        Joerg Roedel <jroedel@suse.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>
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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