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

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Date:   Tue, 19 Sep 2023 09:02:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     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 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.