linux-hardening - Re: [PATCH v9 03/15] kallsyms: Hide layout

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Message-ID: <Yc40UKmylVh38vl5@zn.tnic>
Date:   Thu, 30 Dec 2021 23:36:00 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     linux-hardening@...r.kernel.org, x86@...nel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Kees Cook <keescook@...omium.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        Ard Biesheuvel <ardb@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Bruce Schlobohm <bruce.schlobohm@...el.com>,
        Jessica Yu <jeyu@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Marios Pomonis <pomonis@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Nicolas Pitre <nico@...xnic.net>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-arch@...r.kernel.org, live-patching@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v9 03/15] kallsyms: Hide layout

On Thu, Dec 23, 2021 at 01:21:57AM +0100, Alexander Lobakin wrote:
> Subject: Re: [PATCH v9 03/15] kallsyms: Hide layout

That title is kinda laconic...

> From: Kristen Carlson Accardi <kristen@...ux.intel.com>
> 
> This patch makes /proc/kallsyms display in a random order, rather

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

> than sorted by address in order to hide the newly randomized address
> layout.

Sorted by address?

My /proc/kallsyms says

$ awk '{ print $1 }' /proc/kallsyms | uniq -c
 119086 0000000000000000

so all the addresses are 0. Aha, and when I list them as root, only then
I see non-null addresses.

So why do we that patch at all?

> alobakin:
> Don't depend FG-KASLR and always do that for unpriviledged accesses

Unknown word [unpriviledged] in commit message, suggestions:
        ['unprivileged', 'underprivileged', 'privileged']

> as suggested by several folks.
> Also, introduce and use a shuffle_array() macro which shuffles an
> array using Fisher-Yates.

Fisher-Yates what?

/me goes and looks at the wikipedia article.

Aha, a Fisher-Yates shuffle algoithm.

Don't be afraid to explain more in your commit messages and make them
more reader-friendly.

> We'll make use of it several more times
> later on.

Not important for this commit.

...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette