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

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Date:   Mon, 18 Sep 2023 11:05:31 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Matteo Rizzo <matteorizzo@...gle.com>,
        "Lameter, Christopher" <cl@...amperecomputing.com>,
        Dave Hansen <dave.hansen@...el.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 Mon, 18 Sept 2023 at 10:39, Ingo Molnar <mingo@...nel.org> wrote:
>
> What's the split of the increase in overhead due to SLAB_VIRTUAL=y, between
> user-space execution and kernel-space execution?

... and equally importantly, what about DMA?

Or what about the fixed-size slabs (aka kmalloc?) What's the point of
"never re-use the same address for a different slab", when the *same*
slab will contain different kinds of allocations anyway?

I think the whole "make it one single compile-time option" model is
completely and fundamentally broken.

                     Linus