linux-kernel - Re: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub

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Date:   Thu, 3 Jun 2021 15:15:24 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v3 4/4] slub: Force on no_hash_pointers when slub_debug
 is enabled

On Tue 2021-06-01 11:22:02, Stephen Boyd wrote:
> Obscuring the pointers that slub shows when debugging makes for some
> confusing slub debug messages:
> 
>  Padding overwritten. 0x0000000079f0674a-0x000000000d4dce17
> 
> Those addresses are hashed for kernel security reasons. If we're trying
> to be secure with slub_debug on the commandline we have some big
> problems given that we dump whole chunks of kernel memory to the kernel
> logs. Let's force on the no_hash_pointers commandline flag when
> slub_debug is on the commandline. This makes slub debug messages more
> meaningful and if by chance a kernel address is in some slub debug
> object dump we will have a better chance of figuring out what went
> wrong.
> 
> Note that we don't use %px in the slub code because we want to reduce
> the number of places that %px is used in the kernel. This also nicely
> prints a big fat warning at kernel boot if slub_debug is on the
> commandline so that we know that this kernel shouldn't be used on
> production systems.
> 
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>

Acked-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr