linux-kernel - Re: [PATCH] lkdtm: Test KUAP directional user access unlocks on powerpc

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Message-ID: <202002010836.76B19684@keescook>
Date:   Sat, 1 Feb 2020 08:40:34 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Russell Currey <ruscur@...sell.cc>
Cc:     Christophe Leroy <christophe.leroy@....fr>, mpe@...erman.id.au,
        linux-kernel@...r.kernel.org, dja@...ens.net,
        kernel-hardening@...ts.openwall.com, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] lkdtm: Test KUAP directional user access unlocks on
 powerpc

On Fri, Jan 31, 2020 at 05:53:14PM +1100, Russell Currey wrote:
> Correct, the ACCESS_USERSPACE test does the same thing.  Splitting this
> into separate R and W tests makes sense, even if it is unlikely that
> one would be broken without the other.

That would be my preference too -- the reason it wasn't separated before
was because it was one big toggle before. I just had both directions in
the test out of a desire for completeness.

Splitting into WRITE_USERSPACE and READ_USERSPACE seems good. Though if
you want to test functionality (read while only write disabled), then
I'm not sure what that should look like. Does the new
user_access_begin() API provide a way to query existing state? I'll go
read the series...

-- 
Kees Cook