linux-kernel - Re: [PATCH v2 1/7] sysfs/cpu: Add "Unknown" vulnerability state

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Message-ID: <20190104101311.GB24160@edgewater-inn.cambridge.arm.com>
Date:   Fri, 4 Jan 2019 10:13:11 +0000
From:   Will Deacon <will.deacon@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Dave Martin <Dave.Martin@....com>, mark.rutland@....com,
        julien.thierry@....com, mlangsdo@...hat.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        suzuki.poulose@....com, marc.zyngier@....com,
        catalin.marinas@....com,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        linux-kernel@...r.kernel.org, steven.price@....com,
        shankerd@...eaurora.org, Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        ykaukab@...e.de, Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/7] sysfs/cpu: Add "Unknown" vulnerability state

On Thu, Jan 03, 2019 at 02:32:44PM -0600, Jeremy Linton wrote:
> On 01/03/2019 01:30 PM, Stefan Wahren wrote:
> > > Jeremy Linton <jeremy.linton@....com> hat am 3. Januar 2019 um 17:46 geschrieben:
> > > On 01/03/2019 10:37 AM, Dave Martin wrote:
> > > > On Wed, Jan 02, 2019 at 06:49:15PM -0600, Jeremy Linton wrote:
> > > > > There is a lot of variation in the Arm ecosystem. Because of this,
> > > > > there exist possible cases where the kernel cannot authoritatively
> > > > > determine if a machine is vulnerable.
> > > > > 
> > > > > Rather than guess the vulnerability status in cases where
> > > > > the mitigation is disabled or the firmware isn't responding
> > > > > correctly, we need to display an "Unknown" state.
> > > > > 
> > 
> > i applied your patch series on linux-next-20190103. On my Raspberry Pi 3B+ (defconfig) i'm getting this from sysfs:
> > 
> > l1tf:Not affected
> > meltdown:Not affected
> > spec_store_bypass:Unknown
> > spectre_v1:Mitigation: __user pointer sanitization
> > spectre_v2:Unknown
> > 
> > AFAIK it has 4 Cortex-A53 cores (no PSCI firmware), so shouldn't be affected.
> 
> So, for spec_store_bypass, as you noted your getting hit by the lack of
> psci/smccc to report the ssb state, and this patch is just reflecting that.
> 
> In the case of spectrev2 it may be correct to blame this patch set because
> its displaying "unknown" since your core isn't in the black list, and your
> core isn't new enough to have the csv2 bit indicating its not vulnerable. In
> this case if we do away with the unknown state, we should probably depend
> entirely on the black list and simply display "Not affected" if the core
> isn't listed. (meaning we may report cores not affected when they are
> missing from the blacklist).
> 
> 
> > How can this be fixed?
> 
> For ssb, the correct answer is probably fix the firmware, but given the
> situation, its likely this kind of machine is going to force an additional
> MIDR list to report the state correctly. Maybe Will or someone can chime in
> here?

Marc Z is already working on this iirc, since we need it to fix the message
printed to dmesg about the mitigation status anyway.

Will