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. grsecurity‏ @grsecurity 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation

      Someone should have told us FB was handing out $100k just to make use of MPK for what it was designed to do

      2 replies 1 retweet 14 likes
    2. Dave dwizzzle Weston‏ @dwizzzleMSFT 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @grsecurity

      Lol your a savage spender

      1 reply 0 retweets 3 likes
    3. grsecurity‏ @grsecurity 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @dwizzzleMSFT

      Not trying to be, I looked at the paper and didn't see what all the hype was about. The press coverage was misleading, trying to make it sound like it was MPK that nobody could use in a performant way, but the paper was talking about alternative methods (hypervisors etc)

      2 replies 0 retweets 1 like
    4. grsecurity‏ @grsecurity 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @grsecurity @dwizzzleMSFT

      And I don't see how looking for two instructions is enough to prevent bypassing of the security, since it seems to assume they have control over mprotect etc, but yet they're not scanning the rw-but-soon-rx maps for mmap/mprotect syscalls that they wouldn't intercept

      2 replies 0 retweets 2 likes
    5. Anjo Vahldiek-Oberwagner‏ @ovahldy 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @grsecurity @dwizzzleMSFT

      Small correction, we do. In the paper we describe and the sources offer two alternative runtime monitors. One is based on a few kernel changes (lsm hooks) + an LSM module, the other combines p-trace and seccomp to filter for certian syscalls. Or am I missing something?

      1 reply 0 retweets 2 likes
    6. grsecurity‏ @grsecurity 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @ovahldy @dwizzzleMSFT

      You're right, missed that part. I still don't think you can get away with avoiding CFI though -- what stops me from having a write() or send() syscall point at a buffer unreadable by the userland thread only by virtue of PKU and just leaking 'protected' memory that way?

      2 replies 0 retweets 0 likes
    7. grsecurity‏ @grsecurity 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @grsecurity @ovahldy @dwizzzleMSFT

      BTW monitoring mmap/mprotect isn't enough ;) I can mmap a file, have you inspect it and allow it to be made executable, then i can extend it with mremap() to include additional code from the file that you don't inspect. Fill blahdata with a page of As and a page of Bspic.twitter.com/FFQOe4BBfa

      1 reply 2 retweets 6 likes
    8. Anjo Vahldiek-Oberwagner‏ @ovahldy 24 Aug 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @grsecurity @dwizzzleMSFT

      Thanks for taking the time. Good catch! You're right that certain system calls like mmap/mprotect/pkey_mprotect/mremap have to be monitored. I'm not sure that we have a complete list in the paper. For instance, we also monitor signal to prevent installing new handlers.

      1 reply 0 retweets 1 like
      Jann Horn‏ @tehjh Apr 21
      • Report Tweet
      • Report NetzDG Violation
      Replying to @ovahldy @grsecurity @dwizzzleMSFT

      by the way, I don't think I've seen your paper (or anyone else) mention that you also have to check whether the CS register contains the correct segment selector in code that is equivalent in 32-bit-mode - AFAIK otherwise something like IRET or long jumps can be abused?

      8:52 AM - 21 Apr 2020
      • 4 Likes
      • Mathias Krause zerons Poete Anjo Vahldiek-Oberwagner
      1 reply 0 retweets 4 likes
        1. New conversation
        2. Anjo Vahldiek-Oberwagner‏ @ovahldy Apr 21
          • Report Tweet
          • Report NetzDG Violation
          Replying to @tehjh @grsecurity @dwizzzleMSFT

          Greatly appreciate your feedback! I'm not familiar with this style of attack, please elaborate? Do you expect existing 32-bit compatibility libraries in application? I was under the impression that the CS register is preserved across syscalls (=0 for x86-64). Feel free to DM.

          1 reply 0 retweets 0 likes
        3. Jann Horn‏ @tehjh Apr 21
          • Report Tweet
          • Report NetzDG Violation
          Replying to @ovahldy @grsecurity @dwizzzleMSFT

          at least on Linux, the GDT that is used across all processes on the system contains an entry for a 32-bit code segment. so you can abuse an instruction like IRET (which is a single-byte instruction) to switch to 32-bit mode from normal 64-bit code.

          1 reply 0 retweets 0 likes
        4. 6 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