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danluu's profile
Dan Luu
Dan Luu
Dan Luu
@danluu

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Dan Luu

@danluu

https://patreon.com/danluu 

danluu.com
Joined December 2008

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    1. Dan Luu‏ @danluu 7 Dec 2019
      • Report Tweet

      This kind of thing is why the CPU startup I worked for allowed users to change the CPUID: you get huge performance gains from putting GenuineIntel in CPUID(0), but it would be a copyright violation to distribute our CPU with GenuineIntel in the CPUID https://www.pugetsystems.com/labs/hpc/How-To-Use-MKL-with-AMD-Ryzen-and-Threadripper-CPU-s-Effectively-for-Python-Numpy-And-Other-Applications-1637/ …pic.twitter.com/HRduiSyypU

      ... The short story is that Intel checks for "Genuine Intel" CPU's when it's numerical library MKL starts executing code. If it find an Intel CPU then it will follow an optimal code path for maximum performance on hardware. If it finds and AMD processor is takes a code path that only optimizes to the old (ancient) SSE2 instruction level ...
      11 replies 318 retweets 797 likes
      Show this thread
    2. Dan Luu‏ @danluu 7 Dec 2019
      • Report Tweet

      That post blames Intel, but it's not just them. NaCl forcibly crashed (and Google refused our trivial fix!!!), random drivers wouldn't work, you had to get a patched Windows installer for multiple releases of Windows (difficult in the days of CD installers), etc.

      2 replies 15 retweets 81 likes
      Show this thread
      Dan Luu‏ @danluu 7 Dec 2019
      • Report Tweet

      Dan Luu Retweeted Dan Luu

      The Google Chromium team banning our CPUs is especially ironic in retrospect since they cited security concerns. At the time, we were mostly shipping in-order CPUs, not vulnerable to Metldown/Spectre/etc. and of course Intel is the most vulnerable these.https://twitter.com/danluu/status/779746231287328768 …

      Dan Luu added,

      Dan Luu @danluu
      Five year anniversary of the bug where Google refuses to allow NaCl to run on non-mainstream CPUs coming up! https://bugs.chromium.org/p/nativeclient/issues/detail?id=2508 … pic.twitter.com/vtXWr3j3QZ
      3:16 PM - 7 Dec 2019
      • 37 Retweets
      • 166 Likes
      • Wesley Baugh Pavel Levchuk Mark Struberg Michael Griffiths Thomas Garner zumdeibel rdwrt Thomas Daede Michał Kawalec
      5 replies 37 retweets 166 likes
        1. Dan Luu‏ @danluu 8 Dec 2019
          • Report Tweet

          BTW, if you want to try CPUID spoofing without virtualization and have a VIA processor, Agner Fog wrote this little utility: https://www.agner.org/optimize/blog/read.php?i=118#73 … Performance delta on benchmarks varies, here's an example of a ~50% gain (47%): https://arstechnica.com/gadgets/2008/07/atom-nano-review/6/ …pic.twitter.com/gLK1cESeRz

          Score with normal CPUID: 1845
Scored with spoofed CPUID: 2721

(higher is better)
          0 replies 8 retweets 29 likes
          Show this thread
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        2. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
          • Report Tweet
          Replying to @danluu @chort0

          The security of NaCL required accurately predicting controlflow, and confidence it would work in adversarial conditions (e.g. someone trying to induce faults, undocumented opcodes, etc.). I said it seemed prudent to whitelist cpus we had tested, I stand by that. 🤷🏻‍♂️

          1 reply 0 retweets 6 likes
        3. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
          • Report Tweet
          Replying to @taviso @danluu @chort0

          If someone overclocks their cpu, and an attacker does some x87 operation in a tight loop for a few minutes, how confident are you a branches won't be miscalculated? Usually no security consequences for this, so vendors didn't test, It worried me 🤷🏻‍♂️e.g.https://devblogs.microsoft.com/oldnewthing/20050412-47/?p=35923 …

          3 replies 4 retweets 7 likes
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        1. Sven Slootweg @ 36C3‏ @joepie91 8 Dec 2019
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          Replying to @danluu

          Clearly the correct solution would have been to take a page from the browser book, and call your CPU "AuthenticAMD (like GenuineIntel)"!

          0 replies 0 retweets 2 likes
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        2. Daniel Bilar‏ @daniel_bilar 7 Dec 2019
          • Report Tweet
          Replying to @danluu

          @threadreaderapp kindly unroll

          1 reply 0 retweets 0 likes
        3. Thread Reader App‏ @threadreaderapp 7 Dec 2019
          • Report Tweet
          Replying to @daniel_bilar

          Halo!, you can read it here: Thread by @danluu: This kind of thing is why the CPU startup I worked for allowed users to change the CPUID: you get… https://threadreaderapp.com/thread/1203450367515615233.html …. Share this if you think it's interesting. 🤖

          0 replies 0 retweets 0 likes
        4. End of conversation
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        2. Marsh Ray‏ @marshray 7 Dec 2019
          • Report Tweet
          Replying to @danluu @brouhaha

          Did your CPU recognize any special opcodes, or in any way handle EIP differently? It’s hard to prove a negative. I think I would have made the same call.

          1 reply 0 retweets 0 likes
        3. Andrew Bingham‏ @marsman2020 8 Dec 2019
          • Report Tweet
          Replying to @marshray @danluu @brouhaha

          Let's make Google the gatekeepers of more stuff, that will be great.

          1 reply 1 retweet 5 likes
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