linux-kernel - Re: [PATCH] mm/slab_common.c: fix possible spectre-v1 in kmalloc

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Date:   Wed, 29 May 2019 19:49:31 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Dianzhang Chen <dianzhangchen0@...il.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/slab_common.c: fix possible spectre-v1 in
 kmalloc_slab()

On Thu 30-05-19 00:39:53, Dianzhang Chen wrote:
> It's come from `192+1`.
> 
> 
> The more code fragment is:
> 
> 
> if (size <= 192) {
> 
>     if (!size)
> 
>         return ZERO_SIZE_PTR;
> 
>     size = array_index_nospec(size, 193);
> 
>     index = size_index[size_index_elem(size)];
> 
> }

OK I see, I could have looked into the code, my bad. But I am still not
sure what is the potential exploit scenario and why this particular path
a needs special treatment while other size branches are ok. Could you be
more specific please?
-- 
Michal Hocko
SUSE Labs