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

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Date:   Fri, 24 Jul 2020 16:25:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Ingo Molnar <mingo@...hat.com>,
        "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>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        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 Sat, Jul 18, 2020 at 08:44:50AM +0300, Ard Biesheuvel wrote:
> On Fri, 17 Jul 2020 at 21:17, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
> >
> > 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?
> 
> That is not the right way to deal with conflicts against -next.
> 
> This series targets the -tip tree, and applies fine against it. If you
> want to apply it on some other tree and test it, that is fine, and
> highly appreciated, but 'refreshing' the series against -next means it
> no longer applies to -tip, and may be based on unidentified conflict
> resolutions performed by Stephen that the maintainers will have to
> deal with.
> 
> Boris, Ingo, Thomas,
> 
> Mind taking v5 of this series? (With Nick's Tested-by) I think these
> patches have been simmering long enough. Do note there is a conflict
> against the kbuild tree, but the resolution should be straightforward.

I would love that; I need to rebase my orphan series on this too...

-- 
Kees Cook