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taviso's profile
Tavis Ormandy
Tavis Ormandy
Tavis Ormandy
Verified account
@taviso

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Tavis OrmandyVerified account

@taviso

Vulnerability researcher at Google. This is a personal stream, opinions expressed are mine.

California
taviso.decsystem.org
Joined April 2008

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    1. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      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 8 likes
    2. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      Replying to @taviso @danluu @chort0

      This wasn't a popular opinion, people worried it would hurt adoption. It probably did, but my job is to worry about security.

      2 replies 1 retweet 2 likes
    3. rdwrt‏ @rdwrt 8 Dec 2019
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      Replying to @taviso @danluu @chort0

      how did any check to make sure the vendor string was "GenuineIntel" stop the security issues caused by Meltdown and Spectre?

      1 reply 0 retweets 1 like
    4. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      Replying to @rdwrt @danluu @chort0

      It didn't, but it likely did prevent trivial shellcode execution on some systems. Does a mitigation have to stop all vulnerabilities to be useful? That would mean there has never been a useful mitigation.

      1 reply 1 retweet 1 like
    5. rdwrt‏ @rdwrt 8 Dec 2019
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      Replying to @taviso @danluu @chort0

      If the mitigation has shown to fail for several important vulnerabilities, it could be an idea to review if other choices would have been just as effective but without the negative side effects that originated from hardcoded exclusion of vendors. It's a spoofable string anyway!

      1 reply 1 retweet 0 likes
    6. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      Replying to @rdwrt @danluu @chort0

      Can you give me an example of a successful mitigation? An attacker cannot spoof the string.

      2 replies 0 retweets 0 likes
    7. Derek Rynd‏ @daax_rynd 8 Dec 2019
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      Replying to @taviso @rdwrt and

      I'm wondering if he means it's "spoofable" in the sense that something like a VMM could modify what is passed back. E.g. trap on CPUID and change the value of the registers. There are ways to get drivers loaded without a cert, but that's all I thought of. Just interjecting.

      1 reply 0 retweets 0 likes
    8. Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      Replying to @daax_rynd @daax_r and

      Sure, but that requires you to have already compromised the system. There's no point trying to interfere with NaCl if you're already a malicious hypervisor, you've already won.

      1 reply 0 retweets 2 likes
    9. Derek Rynd‏ @daax_rynd 8 Dec 2019
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      Replying to @taviso @rdwrt and

      Oh yeah of course, I'm not arguing just speculating with their original comment since he didn't answer.

      1 reply 0 retweets 1 like
    10. rdwrt‏ @rdwrt 8 Dec 2019
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      Replying to @daax_rynd @daax_r and

      You show that selecting on vendor string was a matter of convenience, not security, as any attack vector would involve building and distributing malicious cpus/devices. If security truly would be the issue, one mitigating measure would be to not run when hyperthreading is enabled

      1 reply 0 retweets 0 likes
      Tavis Ormandy‏Verified account @taviso 8 Dec 2019
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      Replying to @rdwrt @daax_r and

      wat

      10:55 PM - 8 Dec 2019
      • 1 Like
      • Derek Rynd
      1 reply 0 retweets 1 like
        1. rdwrt‏ @rdwrt 8 Dec 2019
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          Replying to @taviso @daax_r and

          rdwrt Retweeted Dan Luu

          wat https://twitter.com/danluu/status/1203452041470730242?s=21 …https://twitter.com/danluu/status/1203452041470730242 …

          rdwrt added,

          Dan Luu @danluu
          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.
          Show this thread
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