Skip to content
By using Twitter’s services you agree to our Cookies Use. We and our partners operate globally and use cookies, including for analytics, personalisation, and ads.

This is the legacy version of twitter.com. We will be shutting it down on June 1, 2020. Please switch to a supported browser, or disable the extension which masks your browser. You can see a list of supported browsers in our Help Center.

  • Home Home Home, current page.
  • About

Saved searches

  • Remove
  • In this conversation
    Verified accountProtected Tweets @
Suggested users
  • Verified accountProtected Tweets @
  • Verified accountProtected Tweets @
  • Language: English
    • Bahasa Indonesia
    • Bahasa Melayu
    • Català
    • Čeština
    • Dansk
    • Deutsch
    • English UK
    • Español
    • Filipino
    • Français
    • Hrvatski
    • Italiano
    • Magyar
    • Nederlands
    • Norsk
    • Polski
    • Português
    • Română
    • Slovenčina
    • Suomi
    • Svenska
    • Tiếng Việt
    • Türkçe
    • Ελληνικά
    • Български език
    • Русский
    • Српски
    • Українська мова
    • עִבְרִית
    • العربية
    • فارسی
    • मराठी
    • हिन्दी
    • বাংলা
    • ગુજરાતી
    • தமிழ்
    • ಕನ್ನಡ
    • ภาษาไทย
    • 한국어
    • 日本語
    • 简体中文
    • 繁體中文
  • Have an account? Log in
    Have an account?
    · Forgot password?

    New to Twitter?
    Sign up
tehjh's profile
Jann Horn
Jann Horn
Jann Horn
@tehjh

Tweets

Jann Horn

@tehjh

works at Google Project Zero. personal account.

Joined August 2011

Tweets

  • © 2020 Twitter
  • About
  • Help Center
  • Terms
  • Privacy policy
  • Imprint
  • Cookies
  • Ads info
Dismiss
Previous
Next

Go to a person's profile

Saved searches

  • Remove
  • In this conversation
    Verified accountProtected Tweets @
Suggested users
  • Verified accountProtected Tweets @
  • Verified accountProtected Tweets @

Promote this Tweet

Block

  • Tweet with a location

    You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more

    Your lists

    Create a new list


    Under 100 characters, optional

    Privacy

    Copy link to Tweet

    Embed this Tweet

    Embed this Video

    Add this Tweet to your website by copying the code below. Learn more

    Add this video to your website by copying the code below. Learn more

    Hmm, there was a problem reaching the server.

    By embedding Twitter content in your website or app, you are agreeing to the Twitter Developer Agreement and Developer Policy.

    Preview

    Why you're seeing this ad

    Log in to Twitter

    · Forgot password?
    Don't have an account? Sign up »

    Sign up for Twitter

    Not on Twitter? Sign up, tune into the things you care about, and get updates as they happen.

    Sign up
    Have an account? Log in »

    Two-way (sending and receiving) short codes:

    Country Code For customers of
    United States 40404 (any)
    Canada 21212 (any)
    United Kingdom 86444 Vodafone, Orange, 3, O2
    Brazil 40404 Nextel, TIM
    Haiti 40404 Digicel, Voila
    Ireland 51210 Vodafone, O2
    India 53000 Bharti Airtel, Videocon, Reliance
    Indonesia 89887 AXIS, 3, Telkomsel, Indosat, XL Axiata
    Italy 4880804 Wind
    3424486444 Vodafone
    » See SMS short codes for other countries

    Confirmation

     

    Welcome home!

    This timeline is where you’ll spend most of your time, getting instant updates about what matters to you.

    Tweets not working for you?

    Hover over the profile pic and click the Following button to unfollow any account.

    Say a lot with a little

    When you see a Tweet you love, tap the heart — it lets the person who wrote it know you shared the love.

    Spread the word

    The fastest way to share someone else’s Tweet with your followers is with a Retweet. Tap the icon to send it instantly.

    Join the conversation

    Add your thoughts about any Tweet with a Reply. Find a topic you’re passionate about, and jump right in.

    Learn the latest

    Get instant insight into what people are talking about now.

    Get more of what you love

    Follow more accounts to get instant updates about topics you care about.

    Find what's happening

    See the latest conversations about any topic instantly.

    Never miss a Moment

    Catch up instantly on the best stories happening as they unfold.

    1. Solar Designer‏ @solardiz 6 Jan 2018
      • Report Tweet
      • Report NetzDG Violation

      Does #Meltdown bypass segment limit? To be specific, is e.g. Linux 2.0 on 32-bit x86 vulnerable? If not, maybe consider http://wiki.osdev.org/X86-64#Segmentation_in_Long_Mode …

      3 replies 7 retweets 10 likes
    2. Daniel Gruss‏ @lavados 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @solardiz

      Probably it does not. The prefetch side-channel attack also did not bypass it: https://gruss.cc/files/prefetch.pdf … And since then we performed more tests. I would be somewhat optimistic that segment limits work against #Meltdown.

      2 replies 0 retweets 2 likes
    3. Solar Designer‏ @solardiz 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @lavados

      In that paper, you dismiss use of segment limits in 64-bit mode because "the CPU can ignore these values at runtime and does not have to perform runtime range checks for memory accesses" - yet it'd be sufficient if they work on specific vulnerable CPUs, so maybe revisit this?

      1 reply 0 retweets 2 likes
    4. Daniel Gruss‏ @lavados 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @solardiz

      segment limits don't work in 64-bit mode for CS and DS, also ES iirc, but FS and GS can have limits (which is convenient for small TLS segments). but if you use 32 bit segments on a 64-bit OS, prefetch and also #meltdown probably won't work from that process anymore.

      2 replies 0 retweets 0 likes
    5. Solar Designer‏ @solardiz 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @lavados

      Oh. Would that be a reason to revisit x32, then? The performance advantage of x32 over x86_64 would suddenly become greater than it was before, right?

      1 reply 1 retweet 8 likes
    6. Daniel Gruss‏ @lavados 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @solardiz

      yes, but at the same time you would limit processes to a comparably small address space. I fear we already got too used to the vast space of 48bit virtual addresses.

      1 reply 0 retweets 2 likes
    7. Solar Designer‏ @solardiz 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @lavados

      Sure. Is x32 as currently implemented in the Linux kernel safe from Meltdown or are minor changes needed (propose them on LKML if so)?

      1 reply 0 retweets 0 likes
      Jann Horn‏ @tehjh 7 Jan 2018
      • Report Tweet
      • Report NetzDG Violation
      Replying to @solardiz @lavados

      x32 isn't architecturally different from x64-64 AFAIK? just a different syscall convention?

      6:52 AM - 7 Jan 2018
      • 1 Like
      • Alexander Nasonov
      1 reply 0 retweets 1 like
        1. New conversation
        2. Daniel Gruss‏ @lavados 7 Jan 2018
          • Report Tweet
          • Report NetzDG Violation
          Replying to @tehjh @solardiz

          and differences in what you can do with segments. and if you're not using a long mode segment you can't use long mode operations -> you can't have pointers that point anywhere above 2^32.

          1 reply 0 retweets 0 likes
        3. Jann Horn‏ @tehjh 7 Jan 2018
          • Report Tweet
          • Report NetzDG Violation
          Replying to @lavados @solardiz

          but the point of x32 is that you do have 64-bit mode, so that you can use R8-R15 and other features of 64-bit mode. x32 uses 32-bit pointers in its calling convention, but it's not architecturally compatibility mode

          1 reply 0 retweets 2 likes
        4. 7 more replies

      Loading seems to be taking a while.

      Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.

        Promoted Tweet

        false

        • © 2020 Twitter
        • About
        • Help Center
        • Terms
        • Privacy policy
        • Imprint
        • Cookies
        • Ads info