linux-kernel - Re: [PATCH v5 11/17] arm64: docs: document pointer authentication

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Message-ID: <05738017-5886-fe4d-e8fd-a834da6b1576@arm.com>
Date:   Fri, 19 Oct 2018 12:47:16 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Kristina Martsenko <kristina.martsenko@....com>
Cc:     Ramana Radhakrishnan <ramana.radhakrishnan@...s.arm.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <Mark.Rutland@....com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Andrew Jones <drjones@...hat.com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Adam Wallis <awallis@...eaurora.org>,
        Suzuki Poulose <Suzuki.Poulose@....com>,
        Will Deacon <Will.Deacon@....com>,
        Christoffer Dall <Christoffer.Dall@....com>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        Amit Kachhap <Amit.Kachhap@....com>,
        Dave P Martin <Dave.Martin@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v5 11/17] arm64: docs: document pointer authentication

On 19/10/18 12:35, Catalin Marinas wrote:
> On Tue, Oct 16, 2018 at 05:14:39PM +0100, Kristina Martsenko wrote:
>> On 05/10/2018 10:04, Ramana Radhakrishnan wrote:
>>> On 05/10/2018 09:47, Kristina Martsenko wrote:

[...]

>> The other option is to turn off trapping entirely. However then on a
>> big.LITTLE system with mismatched pointer authentication support
>> instructions will work intermittently on some CPUs but not others.
> 
> That's another case but let's assume we never see such configurations ;).

I'd like to put it on the record that I'm not willing to support such a
configuration. So my ask is that if we detect a system where only some
of the CPUs have pointer authentication support, we either:

1) prevent some of the CPUs from booting (that's harsh)
2) disable KVM (that's easy)

I'm perfectly happy with (2).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...