linux-kernel - Re: [RFCv2 2/4] Documentation: document nospec helpers

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Date:   Sun, 7 Jan 2018 13:06:11 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        dan.j.williams@...el.com, elena.reshetova@...el.com,
        corbet@....net, alan@...ux.intel.com, peterz@...radead.org,
        will.deacon@....com, gregkh@...uxfoundation.org,
        tglx@...utronix.de, Paul Turner <pjt@...gle.com>
Subject: Re: [RFCv2 2/4] Documentation: document nospec helpers

On Sat, Jan 06, 2018 at 09:20:59PM -0800, Randy Dunlap wrote:
> On 01/05/18 06:57, Mark Rutland wrote:
> > Document the rationale and usage of the new nospec*() helpers.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Signed-off-by: Will Deacon <will.deacon@....com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > ---
> >  Documentation/speculation.txt | 166 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 166 insertions(+)
> >  create mode 100644 Documentation/speculation.txt
> > 
> > diff --git a/Documentation/speculation.txt b/Documentation/speculation.txt
> > new file mode 100644
> > index 000000000000..748fcd4dcda4
> > --- /dev/null
> > +++ b/Documentation/speculation.txt
> > @@ -0,0 +1,166 @@
> > +
> > +Typically speculative execution cannot be observed from architectural state,
> > +such as the contents of registers. However, in some cases it is possible to
> > +observe its impact on microarchitectural state, such as the presence or
> > +absence of data in caches. Such state may form side-channels which can be
> > +observed to extract secret information.
> 
> I'm curious about what it takes to observe this...
> 
> or is that covered in the exploit papers?

That's covered elsewhere, e.g.

https://googleprojectzero.blogspot.co.uk/2018/01/reading-privileged-memory-with-side.html

I'll add some references.

Thanks,
Mark.