linux-hardening - RE: [RFC PATCH 12/17] gcc-plugins: objtool: Add plugin to detect switch table on arm64

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Date:   Tue, 2 Feb 2021 14:24:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Josh Poimboeuf' <jpoimboe@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
CC:     Julien Thierry <jthierry@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Peter Zijlstra <peterz@...radead.org>,
        "raphael.gault@....com" <raphael.gault@....com>,
        Will Deacon <will@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Bill Wendling <morbo@...gle.com>
Subject: RE: [RFC PATCH 12/17] gcc-plugins: objtool: Add plugin to detect
 switch table on arm64

Stirring more goop into the hole ....

Requiring gcc-plugins, matching compiler versions and the
same 'dwarf' format for OOT modules is probably very painful.

In many cases (and this may include drivers released by some
distributions) an OOT driver has two separate parts.

One part is C source that is compiled when the module is built
on the target system and against the installed kernel headers.
Getting this to match 'just' relies on having the correct
compiler (etc) installed and in $PATH.

The second part is much more problematic.
This is just an object file compiled by a third party.
It doesn't directly depend on anything defined in the
kernel headers - so can (currently) be linked into any
kernel version.

In the past some graphics drivers have had a third party
object file.
I think some of the laptop wifi drivers might as well.

Now I some people think everything should be free source.
But there are various commercial and practical reasons
for both OOT drivers and object file 'blobs' in OOT drivers.

	David

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