linux-kernel - Re: [PATCH v6 10/11] mm: add a user_virt_to

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Message-ID: <20170911073616.GA23201@infradead.org>
Date:   Mon, 11 Sep 2017 00:36:16 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Tycho Andersen <tycho@...ker.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Marco Benatto <marco.antonio.780@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v6 10/11] mm: add a user_virt_to_phys symbol

On Fri, Sep 08, 2017 at 08:44:22AM -0700, Kees Cook wrote:
> On Fri, Sep 8, 2017 at 12:55 AM, Christoph Hellwig <hch@...radead.org> wrote:
> > On Thu, Sep 07, 2017 at 11:36:08AM -0600, Tycho Andersen wrote:
> >> We need someting like this for testing XPFO. Since it's architecture
> >> specific, putting it in the test code is slightly awkward, so let's make it
> >> an arch-specific symbol and export it for use in LKDTM.
> >
> > We really should not add an export for this.
> >
> > I think you'll want to just open code it in your test module.
> 
> Isn't that going to be fragile? Why not an export?

It is a little fragile, but it is functionality not needed at all by
the kernel, so we should not add it to the kernel image and/or export
it.