linux-kernel - Re: [PATCH v4 0/7] x86/boot: Remove runtime relocations from compressed kernel

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Message-ID: <20200714203326.GC902932@rani.riverdale.lan>
Date:   Tue, 14 Jul 2020 16:33:26 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "H . J . Lu" <hjl@...rceware.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/7] x86/boot: Remove runtime relocations from
 compressed kernel

On Tue, Jul 14, 2020 at 10:24:07PM +0200, Sedat Dilek wrote:
> On Tue, Jul 14, 2020 at 10:21 PM Arvind Sankar <nivedita@...m.mit.edu> wrote:
> >
> > On Tue, Jul 14, 2020 at 10:08:04PM +0200, Sedat Dilek wrote:
> > > > >
> > > > > In any case, I think the right fix here would be to add -pie and
> > > > > --no-dynamic-linker to LDFLAGS_vmlinux instead of KBUILD_LDFLAGS.
> > > >
> > > > Hmm, you might be right with moving to LDFLAGS_vmlinux.
> > > >
> > >
> > > We will need the "ifndef CONFIG_LD_IS_LLD" as -r and -pie cannot be
> > > used together.
> > > Is that the or not the fact when moving to LDFLAGS_vmlinux?
> >
> > LDFLAGS_vmlinux will only be used to link boot/compressed/vmlinux,
> > whereas KBUILD_LDFLAGS is used for all linker invocations, and in
> > particular the little link to do the modversions stuff ends up using it.
> >
> > So once we move -pie --no-dynamic-linker to the more correct
> > LDFLAGS_vmlinux and/or stop modversions running, we'll be fine. Being
> > able to use -pie with lld is one of the goals of this series.
> >
> 
> OK, I am doing a new full kernel build with:
> 
> $ git diff arch/x86/boot/compressed/Makefile
> diff --git a/arch/x86/boot/compressed/Makefile
> b/arch/x86/boot/compressed/Makefile
> index 789d5d14d8b0..056a738e47c6 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -51,7 +51,7 @@ UBSAN_SANITIZE :=n
>  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
>  # Compressed kernel should be built as PIE since it may be loaded at any
>  # address by the bootloader.
> -KBUILD_LDFLAGS += -pie $(call ld-option, --no-dynamic-linker)
> +LDFLAGS_vmlinux += -pie $(call ld-option, --no-dynamic-linker)
>  LDFLAGS_vmlinux := -T
> 
>  hostprogs      := mkpiggy
> 
> - Sedat -

That needs to be in just one line (or with the += on the -T line)
LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker) -T

Your second assignment will blow away the -pie.. flags.