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From: Jann Horn <jannh@google.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: wad@chromium.org, Kees Cook <keescook@chromium.org>,
	Linux API <linux-api@vger.kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linuxram@us.ibm.com, Andy Lutomirski <luto@amacapital.net>,
	msammler@mpi-sws.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC PATCH] seccomp: Add protection keys into seccomp_data
Date: Mon, 29 Oct 2018 17:48:30 +0100
Message-ID: <CAG48ez1mY7Osdsc4iJ1JKq=C60wb9bQF=aHbi1fb=pb_V2XMJA@mail.gmail.com> (raw)
In-Reply-To: <7d93080b-68bd-7563-bd3b-e7ee1545e367@intel.com>

On Mon, Oct 29, 2018 at 5:37 PM Dave Hansen <dave.hansen@intel.com> wrote:
> On 10/29/18 9:25 AM, Kees Cook wrote:
> > On Mon, Oct 29, 2018 at 4:23 AM, Michael Sammler <msammler@mpi-sws.org> wrote:
> >> Add the current value of an architecture specific protection keys
> >> register (currently PKRU on x86) to data available for seccomp-bpf
> >> programs to work on. This allows filters based on the currently
> >> enabled protection keys.
>
> How does the current "assignment" of protection keys to the various uses
> get communicated to the filter?

I assume that you first allocate your protection keys, then install the filter?

> I'm not sure this is a great use for PKRU.  I *think* the basic problem
> is that you want to communicate some rights information down into a
> filter, and you want to communicate it with PKRU.  While it's handy to
> have an extra register that nobody (generally) mucks with, I'm not quite
> convinced that we want to repurpose it this way.

That's not how I understand it; I believe that the context is probably
https://arxiv.org/pdf/1801.06822.pdf ?
My understanding is that PKRU is used for lightweight in-process
sandboxing, and to extend this sandbox protection to the syscall
interface, it is necessary to expose PKRU state to seccomp filters.
In other words, this isn't using PKRU exclusively for passing rights
into a filter, but it has to use PKRU anyway.

> Also, I'm not sure the kernel provides the PKRU guarantees you want at
> the moment.  Our implementation *probably* works, but it's mostly by
> accident.

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-29 11:23 Michael Sammler
2018-10-29 16:25 ` Kees Cook
2018-10-29 16:37   ` Dave Hansen
2018-10-29 16:48     ` Jann Horn [this message]
2018-10-29 17:02       ` Michael Sammler
2018-10-29 17:07         ` Dave Hansen
2018-10-29 17:29       ` Dave Hansen
2018-10-29 21:55         ` Michael Sammler
2018-10-29 22:33           ` Dave Hansen
2018-10-30 10:55             ` Michael Sammler
2018-10-29 16:42   ` Jann Horn
2018-10-29 16:48   ` Ram Pai
2018-10-29 17:05     ` Michael Sammler

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