linux-kernel - Re: [PATCH v5 0/7] x86/boot: Remove run-time relocations from compressed kernel

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Message-ID: <CAKwvOdnTbatx8VB-rJSzyFPwfYnkMYK28yLBn1G+hUu8dyfYRA@mail.gmail.com>
Date:   Fri, 17 Jul 2020 11:16:56 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "H . J . Lu" <hjl@...rceware.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 0/7] x86/boot: Remove run-time relocations from
 compressed kernel

On Fri, Jul 17, 2020 at 6:46 AM Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Tue, Jul 14, 2020 at 08:41:26PM -0400, Arvind Sankar wrote:
> > The compressed kernel currently contains bogus run-time relocations in
> > the startup code in head_{32,64}.S, which are generated by the linker,
> > but must not actually be processed at run-time.
> >
> > This generates warnings when linking with the BFD linker, and errors
> > with LLD, which defaults to erroring on run-time relocations in read-only
> > sections. It also requires the -z noreloc-overflow hack for the 64-bit
> > kernel, which prevents us from linking it as -pie on an older BFD linker
> > (<= 2.26) or on LLD, because the locations that are to be apparently
> > relocated are only 32-bits in size and so cannot really have
> > R_X86_64_RELATIVE relocations.
> >
> > This series aims to get rid of these relocations. I've build- and
> > boot-tested with combinations of clang/gcc-10 with lld/bfd-2.34, and
> > gcc-4.9.0 with bfd-2.24, skipping clang on 32-bit because it currently
> > has other issues [0].
> >
>
> Hi Thomas, Ingo, Borislav, would you be able to take a look over this
> series in time for 5.9?

Hi Arvind, thanks for the series; I'm behind on testing.  When I try
to apply this series on top of linux-next, I get a collision in
drivers/firmware/efi/libstub/Makefile:27 when applying "0002
x86/boot/compressed: Force hidden visibility for all symbol
references". Would you mind refreshing the series to avoid that
collision?
-- 
Thanks,
~Nick Desaulniers