linux-kernel - Re: [PATCH v6 2/8] lib: prepare xxhash for preboot environment

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <202007071947.5E9723AF48@keescook>
Date:   Tue, 7 Jul 2020 19:49:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Nick Terrell <nickrterrell@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Chris Mason <clm@...com>,
        linux-kbuild@...r.kernel.org, x86@...nel.org,
        gregkh@...uxfoundation.org, Petr Malat <oss@...at.biz>,
        Kernel Team <Kernel-team@...com>,
        Adam Borowski <kilobyte@...band.pl>,
        Patrick Williams <patrickw3@...com>, rmikey@...com,
        mingo@...nel.org, Patrick Williams <patrick@...cx.xyz>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Norbert Lange <nolange79@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Terrell <terrelln@...com>
Subject: Re: [PATCH v6 2/8] lib: prepare xxhash for preboot environment

On Tue, Jul 07, 2020 at 05:59:25PM -0400, Arvind Sankar wrote:
> On Mon, Jul 06, 2020 at 08:45:58PM -0700, Nick Terrell wrote:
> > From: Nick Terrell <terrelln@...com>
> > 
> > Don't export symbols if XXH_PREBOOT is defined.
> > 
> > This change is necessary to get xxhash to work in a preboot environment,
> > which is needed to support zstd-compressed kernels.
> 
> The usual way to do it is by adding -D__DISABLE_EXPORTS to the CFLAGS, which will
> cause EXPORT_SYMBOL to be stubbed out. Doesn't that work here?

This is quite rare, actually:

$ git grep DISABLE_EXPORTS
arch/s390/purgatory/Makefile:CFLAGS_sha256.o := -D__DISABLE_EXPORTS
arch/x86/boot/compressed/kaslr.c:#define __DISABLE_EXPORTS
arch/x86/purgatory/Makefile:CFLAGS_sha256.o := -D__DISABLE_EXPORTS
drivers/firmware/efi/libstub/Makefile: -D__DISABLE_EXPORTS
include/linux/export.h:#if !defined(CONFIG_MODULES) || defined(__DISABLE_EXPORTS)

But yes, it seems that would be the better approach.

-- 
Kees Cook