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

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Date:   Tue, 18 Sep 2018 18:15:51 +0100
From:   Will Deacon <will.deacon@....com>
To:     Robert Richter <robert.richter@...ium.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 Tue, Sep 18, 2018 at 11:52:27AM +0200, Robert Richter wrote:
> 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?

Ok, I see what you mean now, thanks. However, it doesn't sound much
different than backporting a patch with dependencies, so I'd rather
avoid adding additional code to treat this case specially.

Will