linux-kernel - Re: [RFC PATCH v1 3/6] powerpc: Add skeleton for Kernel Userspace Execution Prevention

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Date:   Wed, 21 Nov 2018 22:50:56 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Russell Currey <ruscur@...sell.cc>,
        Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v1 3/6] powerpc: Add skeleton for Kernel Userspace Execution Prevention

Russell Currey <ruscur@...sell.cc> writes:

> On Wed, 2018-11-07 at 16:56 +0000, Christophe Leroy wrote:
>> This patch adds a skeleton for Kernel Userspace Execution Prevention.
>> 
>> Then subarches implementing it have to define CONFIG_PPC_HAVE_KUEP
>> and provide setup_kuep() function.
>> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>
> An open question (with nothing to do specifically with this patch):
>
> For what reason would you ever disable execution prevention?  Clearly
> there must be something since "nosmep" is a thing, but I don't know why
> we'd ever do it.

Because depending on the implementation there might be a performance
overhead, and you may want to avoid that.

cheers