linux-kernel - Re: [PATCH 4/4] x86/boot: Check that there are no runtime relocations

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Date:   Sun, 24 May 2020 19:57:48 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Fangrui Song <maskray@...gle.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>,
        Dmitry Golovin <dima@...ovin.in>,
        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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] x86/boot: Check that there are no runtime relocations

On Sun, May 24, 2020 at 04:36:07PM -0700, Fangrui Song wrote:
> 
> `grep -qF .rel.local` from 98f78525371b55ccd1c480207ce10296c72fa340
> may be incorrect.. None of these synthesized dynamic relocation sections is
> called *.rel.local* ...
> (it probably wanted to name .rel.data.rel.ro or .rel.data)
> 
> 
> Reviewed-by: Fangrui Song <maskray@...gle.com>

At least from gcc you get .data.rel.local sections if you have, for eg:
	struct { void *p; } foo = { .p = &bar };
where bar is defined in the same file. These aren't relocation sections,
foo is actually placed in the .data.rel.local section instead of .data.

But yeah, it's incomplete, you wouldn't catch it if bar was external
(foo goes in .data.rel) or foo was const (foo goes in .data.rel.ro*).