linux-kernel - Re: [RFCv2 4/4] bpf: inhibit speculated out-of-bounds pointers

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Date:   Fri, 5 Jan 2018 08:38:43 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch@...r.kernel.org,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Alan Cox <alan@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFCv2 4/4] bpf: inhibit speculated out-of-bounds pointers

On Fri, Jan 5, 2018 at 6:57 AM, Mark Rutland <mark.rutland@....com> wrote:
> Note: this patch is an *example* use of the nospec API. It is understood
> that this is incomplete, etc.
>
> Under speculation, CPUs may mis-predict branches in bounds checks. Thus,
> memory accesses under a bounds check may be speculated even if the
> bounds check fails, providing a primitive for building a side channel.
>
> The EBPF map code has a number of such bounds-checks accesses in
> map_lookup_elem implementations. This patch modifies these to use the
> nospec helpers to inhibit such side channels.
>
> The JITted lookup_elem implementations remain potentially vulnerable,
> and are disabled (with JITted code falling back to the C
> implementations).

Do we still need this given this patch from the bpf folks:

    https://patchwork.ozlabs.org/patch/855911/

?