Date: Mon, 8 Jan 2018 18:22:20 +0000
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
To: Will Deacon <will.deacon@arm.com>
Cc: Jayachandran C <jnair@caviumnetworks.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        linux-arm-kernel@lists.infradead.org, lorenzo.pieralisi@arm.com,
        ard.biesheuvel@linaro.org, catalin.marinas@arm.com,
        linux-kernel@vger.kernel.org, labbott@redhat.com,
        christoffer.dall@linaro.org
Subject: Re: [v2,03/11] arm64: Take into account ID_AA64PFR0_EL1.CSV3
Message-ID: <20180108182220.34233ebc@alans-desktop>
In-Reply-To: <20180108175100.GW25869@arm.com>
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        <20180108175100.GW25869@arm.com>
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> > On systems that are not vulnerable to variant 3, this is an unnecessary
> > overhead.  
> 
> KASLR can be bypassed on CPUs that are not vulnerable to variant 3 simply
> by timing how long accesses to kernel addresses from EL0 take -- please read
> the original KAISER paper for details about that attack on x86. kpti
> mitigates that. If you don't care about KASLR, don't enable it (arguably
> it's useless without kpti).

KASLR is primarily of value for remote protection.

Alan