linux-kernel - Re: [PATCH v9 08/11] x86/boot/64: Adapt assembly for PIE support

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Message-ID: <CAJcbSZGfHDthCz4h_h19zGN5Mb9yC+2FCfKs7-rfCuF=G9rP3w@mail.gmail.com>
Date:   Tue, 29 Oct 2019 14:29:53 -0700
From:   Thomas Garnier <thgarnie@...omium.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Maran Wilson <maran.wilson@...cle.com>,
        Feng Tang <feng.tang@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 08/11] x86/boot/64: Adapt assembly for PIE support

On Fri, Aug 9, 2019 at 10:29 AM Borislav Petkov <bp@...en8.de> wrote:
>
> chOn Tue, Jul 30, 2019 at 12:12:52PM -0700, Thomas Garnier wrote:
> > Change the assembly code to use only relative references of symbols for the
> > kernel to be PIE compatible.
> >
> > Early at boot, the kernel is mapped at a temporary address while preparing
> > the page table. To know the changes needed for the page table with KASLR,
>
> These manipulations need to be done regardless of whether KASLR is
> enabled or not. You're basically accomodating them to PIE.
>
> > the boot code calculate the difference between the expected address of the
>
> calculates
>
> > kernel and the one chosen by KASLR. It does not work with PIE because all
> > symbols in code are relatives. Instead of getting the future relocated
> > virtual address, you will get the current temporary mapping.
>
> Please avoid "you", "we" etc personal pronouns in commit messages.
>
> > Instructions were changed to have absolute 64-bit references.
>
> From Documentation/process/submitting-patches.rst:
>
>  "Describe your changes in imperative mood, e.g. "make xyzzy do frotz"
>   instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy
>   to do frotz", as if you are giving orders to the codebase to change
>   its behaviour."

Sorry for the late reply, busy couple months.

I will integrate your feedback in v10. Thanks.

>
> Thx.
>
> --
> Regards/Gruss,
>     Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.