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tehjh's profile
Jann Horn
Jann Horn
Jann Horn
@tehjh

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Jann Horn

@tehjh

works at Google Project Zero. personal account.

Joined August 2011

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    1. Matthew Garrett‏ @mjg59 21 May 2019
      • Report Tweet
      • Report NetzDG Violation

      https://github.com/mjg59/linux/commit/1fa28d39024cebb051319c5a15f8f6f2777b8d72 … - when the thing with the comment "This should be called early in the kernel init sequence" can't be called sufficiently early

      1 reply 0 retweets 13 likes
    2. Jann Horn‏ @tehjh 21 May 2019
      • Report Tweet
      • Report NetzDG Violation
      Replying to @mjg59

      eww. what do you want that for? that's before the page allocator setup

      1 reply 0 retweets 0 likes
    3. Jann Horn‏ @tehjh 21 May 2019
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      Replying to @tehjh @mjg59

      are you trying to provide a filter for boot cmdline flags or what?

      1 reply 0 retweets 0 likes
    4. Matthew Garrett‏ @mjg59 21 May 2019
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      Replying to @tehjh

      Yes, there's some stuff we want to be able to block that could otherwise be overridden by early command line parsing

      1 reply 0 retweets 0 likes
    5. Jann Horn‏ @tehjh 21 May 2019
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      Replying to @mjg59

      but if someone can mess with the command line, can't they majorly screw up the entire boot process anyway?

      1 reply 0 retweets 0 likes
    6. Matthew Garrett‏ @mjg59 21 May 2019
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      Replying to @tehjh

      No?

      1 reply 0 retweets 0 likes
    7. Matthew Garrett‏ @mjg59 21 May 2019
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      Replying to @mjg59 @tehjh

      I mean yeah they can DoS it, but…

      1 reply 0 retweets 0 likes
    8. Jann Horn‏ @tehjh 21 May 2019
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      Replying to @mjg59

      does that mean you're fine with someone being able to set stuff like "root=" but not some other things?

      2 replies 0 retweets 0 likes
      Jann Horn‏ @tehjh 21 May 2019
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      Replying to @tehjh @mjg59

      taking a step back, your premise is "we get the cmdline from the bootloader, and the bootloader is trusted, but we want the bootloader to be able to load a cmdline from disk that can't be verified and just shove it into the kernel", right?

      4:12 PM - 21 May 2019
      • 1 Like
      • Drew Suarezͣ̑ͧ̊̌̋̍
      2 replies 0 retweets 1 like
        1. New conversation
        2. Matthew Garrett‏ @mjg59 21 May 2019
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          • Report NetzDG Violation
          Replying to @tehjh

          We can't assert that the command line is trusted because there are too many cases where you need to modify parameters

          1 reply 0 retweets 0 likes
        3. Jann Horn‏ @tehjh 21 May 2019
          • Report Tweet
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          Replying to @mjg59

          it sounds to me like part of the problem is that the cmdline contains multiple things mixed together and you don't know which part is from where? whether it's from the distro or a config file on the system (which I guess you don't want to trust) or a hint about where the disk is

          1 reply 0 retweets 0 likes
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        1. chris‏ @hugelgupf 21 May 2019
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          Replying to @tehjh @mjg59

          If you have control over the kernel, can't you force those features to be off in code?

          0 replies 0 retweets 0 likes
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