linux-kernel - Re: [PATCH RESEND 3/6] arm64: add sysfs vulnerability show for spectre v1

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Message-ID: <20180918095226.GJ3795@rric.localdomain>
Date:   Tue, 18 Sep 2018 11:52:27 +0200
From:   Robert Richter <robert.richter@...ium.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Mian Yousaf Kaukab <ykaukab@...e.de>, marc.zyngier@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        cwu@...erecomputing.com
Subject: Re: [PATCH RESEND 3/6] arm64: add sysfs vulnerability show for
 spectre v1

On 18.09.18 09:38:05, Will Deacon wrote:
> On Mon, Sep 17, 2018 at 07:22:07PM +0200, Robert Richter wrote:
> > On 27.08.18 16:33:07, Mian Yousaf Kaukab wrote:
> > > Hard-coded since patches are merged and there are no configuration
> > > options.
> >
> > Could you add a list of upstream patches to the description that are
> > required to solve this? This would be a strict definition for the
> > mitigation being enabled and makes it easier to check if backports are
> > affected or not. A build-time check would be ideal (e.g. checking for
> > certain macros).
> 
> Hmm, I don't grok what you're proposing here. Why do we need a build-time
> check (and to check what?)

My concern is, that for kernel backports (esp. distro kernels) there
could be various interpretations of what "Mitigation: __user pointer
sanitization" means. So a list of upstream patches that need to be
backported in addition to this patch as a requirement would be good to
agree on. That should be documented in the patch description.

If these mitigations are available in a kernel backport, that could be
even checked at build time. E.g. we could have a sanity check if the
macro array_index_nospec() is defined. But such a check does not
replace a code review of a kernel backport.

I hope that makes sense?

-Robert