linux-kernel - Re: [RFC PATCH 06/11] x86: make sure

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Message-ID: <43b7ba31-6dca-488b-8a0e-72d9fdfd1a6b@linux.intel.com>
Date:   Mon, 10 Feb 2020 07:54:58 -0800
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        rick.p.edgecombe@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC PATCH 06/11] x86: make sure _etext includes function
 sections

> 
> I'll leave it to others to figure out the exact details. But afaict it
> should be possible to have fine-grained-randomization and preserve the
> workaround in the end.
> 

the most obvious "solution" is to compile with an alignment of 4 bytes (so tight packing)
and then in the randomizer preserve the offset within 32 bytes, no matter what it is

that would get you an average padding of 16 bytes which is a bit more than now but not too insane
(queue Kees' argument that tiny bits of padding are actually good)