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Subject: Re: [PATCH v2 1/7] sysfs/cpu: Add "Unknown" vulnerability state
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
        will.deacon@arm.com, marc.zyngier@arm.com, suzuki.poulose@arm.com,
        dave.martin@arm.com, shankerd@codeaurora.org, mark.rutland@arm.com,
        linux-kernel@vger.kernel.org, ykaukab@suse.de,
        julien.thierry@arm.com, mlangsdo@redhat.com, steven.price@arm.com,
        Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        David Woodhouse <dwmw@amazon.co.uk>
References: <20190103004921.1928921-1-jeremy.linton@arm.com>
 <20190103004921.1928921-2-jeremy.linton@arm.com>
 <20190103093858.GA10794@kroah.com>
From:   Jeremy Linton <jeremy.linton@arm.com>
Message-ID: <c9e08010-3ca0-cb03-e5ad-ab19342ff63b@arm.com>
Date:   Thu, 3 Jan 2019 10:38:16 -0600
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On 01/03/2019 03:38 AM, Greg Kroah-Hartman 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.
> 
> Really?  Why not?  What keeps you from "knowing" this?  Can't the
> developer of the chip tell you?

There tends to be a few cases, possibly incomplete white/black lists, 
firmware that isn't responding correctly, or the user didn't build in 
the code to check the mitigation (possibly because its an embedded 
system and they know its not vulnerable?).

I would hope that it is an exceptional case.

> 
>> 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.
> 
> Shouldn't "Unknown" really be the same thing as "Vulnerable"?  A user
> should treat it the same way, "Unknown" makes it feel like "maybe I can
> just ignore this and hope I really am safe", which is not a good idea at
> all.

I tend to agree its not clear what to do with "unknown".

OTOH, I think there is a hesitation to declare something vulnerable when 
it isn't. Meltdown for example, is fairly rare given that it currently 
only affects a few arm parts, so declaring someone vulnerable when they 
likely aren't is going to be just as difficult to explain.