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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. musl libc‏ @musllibc 15 Feb 2016

      Recent informative ML thread: List of security features in musl. http://www.openwall.com/lists/musl/2016/02/11/4 …

      2 replies 22 retweets 16 likes
    2. CopperheadOS‏ @CopperheadOS 16 Feb 2016
      Replying to @musllibc

      @musllibc @RichFelker Protecting the setjmp registers and internal function pointers (vdso, atexit, atfork) is one of the missing pieces.

      1 reply 0 retweets 0 likes
    3. CopperheadOS‏ @CopperheadOS 16 Feb 2016
      Replying to @CopperheadOS

      @musllibc @RichFelker Could extend RELRO or use a page-aligned/padded global data structure for vdso function pointers, etc. like Bionic.

      1 reply 0 retweets 0 likes
    4. CopperheadOS‏ @CopperheadOS 16 Feb 2016
      Replying to @CopperheadOS

      @musllibc @RichFelker Bionic and glibc use the XOR mitigation for setjmp. Bionic does it for all of the registers. Not sure about glibc.

      1 reply 0 retweets 0 likes
    5. CopperheadOS‏ @CopperheadOS 16 Feb 2016
      Replying to @CopperheadOS

      @musllibc @RichFelker Then there's a choice between OpenBSD-style memory protection and/or glibc-style XOR for atexit, pthread_atfork, etc.

      2 replies 0 retweets 1 like
    6. CopperheadOS‏ @CopperheadOS 16 Feb 2016
      Replying to @CopperheadOS

      @musllibc @RichFelker It'd also be awesome if musl had a compile-time opt-in to a security-focused allocator like an OpenBSD malloc port.

      1 reply 0 retweets 0 likes
      Rich Felker‏ @RichFelker 16 Feb 2016
      Replying to @CopperheadOS

      @CopperheadSec I'd rather see a list of malloc security goals and see if we could meet most in the next-gen production-quality malloc.

      4:32 PM - 16 Feb 2016
      2 replies 0 retweets 0 likes
        1. New conversation
        2. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @RichFelker

          @RichFelker Aiming for performance leads to a much different design. A hardened allocator doesn't have inline metadata. Can't do both well.

          1 reply 0 retweets 0 likes
        3. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker Relying on inline metadata ends up ruling out good security properties like a guaranteed abort for free(any_invalid_address).

          2 replies 0 retweets 0 likes
        4. Rich Felker‏ @RichFelker 16 Feb 2016
          Replying to @CopperheadOS

          @CopperheadSec How so? Check header==(footer^secret). This will, with high probability, catch invalid frees.

          1 reply 0 retweets 0 likes
        5. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @RichFelker

          @RichFelker Not at all the same. Uninitialized data access and out-of-bounds reads (especially one element past the end) are very common.

          1 reply 0 retweets 0 likes
        6. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker It's not the only missing guarantee anyway. It's just one example a nice security property gained from non-inline metadata.

          1 reply 0 retweets 0 likes
        7. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker Anyway, if you have headers and/or footers, it's not comparable to modern performance-oriented allocators without that overhead.

          2 replies 0 retweets 0 likes
        8. Rich Felker‏ @RichFelker 16 Feb 2016
          Replying to @CopperheadOS

          @CopperheadSec I'm generally of the view that "modern performance-oriented allocators" are a load of crap. :-)

          2 replies 0 retweets 0 likes
        9. Rich Felker‏ @RichFelker 16 Feb 2016
          Replying to @RichFelker

          @CopperheadSec Headers/footers, if validated well, also go a long way towards mitigating exploitable off-by-1 heap overflows.

          1 reply 0 retweets 0 likes
        10. 2 more replies
        1. New conversation
        2. Rich Felker‏ @RichFelker 16 Feb 2016
          Replying to @RichFelker

          @CopperheadSec Last I checked the memory waste and performance costs of OpenBSD malloc made it completely unsuitable for production use IMO.

          1 reply 0 retweets 0 likes
        3. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @RichFelker

          @RichFelker It uses a zone-based design which results in lower memory usage than dlmalloc-style allocators. It does use coarse size classes.

          1 reply 0 retweets 0 likes
        4. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker The coarse size classes aren't an inherent property of the design though. It's just the fragmentation trade-off they picked.

          1 reply 0 retweets 0 likes
        5. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker The performance for allocations smaller than the page size is fine, but it lacks thread caches to amortize the locking costs.

          2 replies 0 retweets 0 likes
        6. Rich Felker‏ @RichFelker 16 Feb 2016
          Replying to @CopperheadOS

          @CopperheadSec Awful space and time overhead is going to be around the 2-20 kB range. Syscall for each alloc/free.

          1 reply 0 retweets 0 likes
        7. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @RichFelker

          @RichFelker Not sure what you mean. The zone-based design results in the overhead per allocation being measured in bits, not bytes.

          1 reply 0 retweets 0 likes
        8. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker It's essentially the same design as jemalloc but jemalloc uses 2MiB aligned regions with headers rather than pages + hash table.

          1 reply 0 retweets 0 likes
        9. CopperheadOS‏ @CopperheadOS 16 Feb 2016
          Replying to @CopperheadOS

          @RichFelker The caching mechanism used in OpenBSD for allocations larger than the page size very naive, sure. Small allocations work well.

          0 replies 0 retweets 0 likes
        10. End of conversation

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