Date: Thu, 4 Jan 2018 13:43:35 -0800 From: Conrad Meyer <cem@freebsd.org> To: Michael Butler <imb@protected-networks.net> Cc: "Klaus P. Ohrhallinger" <k@7he.at>, freebsd-current <freebsd-current@freebsd.org>, jan.kokemueller@gmail.com Subject: Re: Intel CPU design flaw - FreeBSD affected? // disabling LDTSC Message-ID: <CAG6CVpVN_wV42R6oswn8rCAMsdruqPrhZarxBcUSXDQyXXKNfQ@mail.gmail.com> In-Reply-To: <02f1caac-b20d-d9bb-ceeb-fd1a2639e6f7@protected-networks.net> References: <9dda0496-be16-35c6-6c45-63d03b218ccb@protected-networks.net> <18376c97-3c0d-49c8-9483-96b95a84f3f1@7he.at> <c675036c-f300-839a-930c-cbe1b4d1c580@gmail.com> <da881926-9ef0-6c69-a9fb-a7594613946a@7he.at> <02f1caac-b20d-d9bb-ceeb-fd1a2639e6f7@protected-networks.net>
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Possibly because Xeon 5400 dates to 2007 =E2=80=94 it may have less advance= d speculative / out-of-order execution and may not have the same branch prediction algorithm as Haswell. On Thu, Jan 4, 2018 at 1:07 PM, Michael Butler <imb@protected-networks.net> wrote: > On 01/04/18 14:59, Klaus P. Ohrhallinger wrote: >> On 04.01.2018 19:51, Jan Kokem=C3=BCller wrote: >> >>> 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/724d4a969fb2c6ae1bbd7b2a9e3d4bb= 6#gistcomment-2311156 >>> [2]: https://blog.mozilla.org/security/2018/01/03/mitigations-landing-n= ew-class-timing-attack/ >> >> I tried the phtread example from [1] but even with some tweaking is does >> not work at all. >> >> This is a multiprocessor system, with moderate load. >> >> As far as I understand the matter, it can only work if both threads >> share the same cpu cache, otherwise the counter variable is either never >> up-to-date, or has to be fetched and stored from/to memory, which is way >> too slow for this purpose. >> >> Any suggestions ? >> >> --- >> >> CPU: Intel(R) Xeon(R) CPU E5420 @ 2.50GHz (2500.14-MHz >> K8-class CPU) >> FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs >> FreeBSD/SMP: 2 package(s) x 4 core(s) > > Interestingly, the Xeon 5400 series is not listed as vulnerable in the > Intel documentation where the 5500 and 5600s are; I checked as I have a > bunch of E5440s in service. > > https://security-center.intel.com/advisory.aspx?intelid=3DINTEL-SA-00088&= languageid=3Den-fr > > imb > > _______________________________________________ > freebsd-current@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org= "
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