linux-hardening - Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator

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Date:   Tue, 19 Sep 2023 10:56:30 -0700
From:   Kees Cook <kees@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>,
        Matteo Rizzo <matteorizzo@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Ingo Molnar <mingo@...nel.org>,
        "Lameter, Christopher" <cl@...amperecomputing.com>,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, vbabka@...e.cz,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-hardening@...r.kernel.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, corbet@....net, luto@...nel.org,
        peterz@...radead.org, jannh@...gle.com, evn@...gle.com,
        poprdi@...gle.com, jordyzomer@...gle.com
Subject: Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator

On September 19, 2023 9:02:07 AM PDT, Dave Hansen <dave.hansen@...el.com> wrote:
>On 9/19/23 08:48, Matteo Rizzo wrote:
>>> I think the whole "make it one single compile-time option" model is
>>> completely and fundamentally broken.
>> Wouldn't making this toggleable at boot time or runtime make performance
>> even worse?
>
>Maybe.
>
>But you can tolerate even more of a performance impact from a feature if
>the people that don't care can actually disable it.
>
>There are also plenty of ways to minimize the overhead of switching it
>on and off at runtime.  Static branches are your best friend here.

Let's start with a boot time on/off toggle (no per-slab, no switch on out-of-space, etc). That should be sufficient for initial ease of use for testing, etc. But yes, using static_branch will nicely DTRT here.



-- 
Kees Cook