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Date:      Thu, 4 Jan 2018 19:51:12 +0100
From:      =?UTF-8?Q?Jan_Kokem=c3=bcller?= <jan.kokemueller@gmail.com>
To:        "Klaus P. Ohrhallinger" <k@7he.at>, freebsd-current@freebsd.org
Subject:   Re: Intel CPU design flaw - FreeBSD affected? // disabling LDTSC
Message-ID:  <c675036c-f300-839a-930c-cbe1b4d1c580@gmail.com>
In-Reply-To: <18376c97-3c0d-49c8-9483-96b95a84f3f1@7he.at>
References:  <9dda0496-be16-35c6-6c45-63d03b218ccb@protected-networks.net> <18376c97-3c0d-49c8-9483-96b95a84f3f1@7he.at>

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On 04.01.2018 19:23, Klaus P. Ohrhallinger wrote:
> All PoC code I have seen today relies on those instructions.
> Is there any other way to measure the memory/cache access times ?

It is possible to emulate a high resolution counter with a thread that
continuously increments a variable [1]. This is the reason why browser
vendors are currently disabling the SharedArrayBuffer feature [2].

[1]: https://gist.github.com/ErikAugust/724d4a969fb2c6ae1bbd7b2a9e3d4bb6#gistcomment-2311156
[2]: https://blog.mozilla.org/security/2018/01/03/mitigations-landing-new-class-timing-attack/



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