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RichFelker's profile
Rich Felker
Rich Felker
Rich Felker
@RichFelker

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Rich Felker

@RichFelker

Yeah, I do @musllibc, FOSS & infosec stuff. But now is not the time for a mostly-/only-tech Twitter feed.

musl-libc.org
Joined March 2014

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    1. Brendan G Bohannon‏ @cr88192 Aug 3

      Idle: half-considering whether to using a UID/GID-style access-rights checking scheme (VUGID) in the BJX2 MMU (in addition to the usual User/Supervisor mechanism). Could add some additional memory-protection features without too much additional cost.

      1 reply 0 retweets 0 likes
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    2. Brendan G Bohannon‏ @cr88192 Aug 3

      Namely, it could allow expressing memory access-rights for groups of pages as seen from a particular thread or control-flow path, allowing code and threads to be sandboxed within a shared address space. Could be helpful for debugging or protection against hostile binary code.

      1 reply 0 retweets 0 likes
      Show this thread
    3. Brendan G Bohannon‏ @cr88192 Aug 3

      IOW: basically, protecting memory regions using a similar scheme to what Unix/Linux uses for protecting files. Possible Drawback: Pretty much nothing does memory-protection this way, so support from existing software would be basically non-existent.

      1 reply 0 retweets 0 likes
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      Rich Felker‏ @RichFelker Aug 3
      Replying to @cr88192

      This isn't any more powerful than a normal MMU; it's just putting a fixed-permission-model hardware unit in place of software (kernel/supervisor) programming of PTEs/TLB to match whatever permission model they want.

      7:08 PM - 3 Aug 2018
      1 reply 0 retweets 0 likes
        1. New conversation
        2. Brendan G Bohannon‏ @cr88192 Aug 3
          Replying to @RichFelker

          It could allow permissions to be done on a per-thread basis though (by giving each its own "keyring"), and with less run-time cost than running all this logic through the PF or TLB miss handlers. Note that this would build on top of a traditional PTE/TLB system, not replace it.

          1 reply 0 retweets 0 likes
        3. Rich Felker‏ @RichFelker Aug 3
          Replying to @cr88192

          Having multiple privilege domains sharing the whole virtual address space (as threads do), not just some mappings, is a huge security problem and inadvisable to try. Normal thread programming models don't do this; you use separate address spaces, not threads, to implement this.

          1 reply 0 retweets 0 likes
        4. Brendan G Bohannon‏ @cr88192 Aug 3
          Replying to @RichFelker

          This is also not intended to replace the use of separate address spaces for processes, but more for use within a process. Probably still better than a large application not having any protection internally (ex: the multi-decade issue of hostile plugins & ActiveX controls, ...).

          1 reply 0 retweets 0 likes
        5. Rich Felker‏ @RichFelker Aug 3
          Replying to @cr88192

          You can't fix utterly wrong Windows architecture with a fancy MMU....

          1 reply 0 retweets 0 likes
        6. Brendan G Bohannon‏ @cr88192 Aug 3
          Replying to @RichFelker

          Variations seem to crop up every few years (often in different forms each time). This feature could better allow keeping plugins from sidestepping their API or 'sandbox'. Granted it is rather unlikely it would be adopted in a mainstream ISA. so mostly just an example here...

          0 replies 0 retweets 0 likes
        7. End of conversation

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