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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. CopperheadOS‏ @CopperheadOS 19 Sep 2015

      So it turns out vanilla Android really only has ~2-3 bits of ASLR entropy for mmap (secondary stacks, dlopen, malloc). That's really sad.

      3 replies 31 retweets 25 likes
    2. CopperheadOS‏ @CopperheadOS 19 Sep 2015
      Replying to @CopperheadOS

      The vanilla Linux ASLR only offers 8 bits of entropy on 32-bit ARM... rather than the 16-20 bits that it should be offering.

      2 replies 8 retweets 9 likes
      Rich Felker‏ @RichFelker 19 Sep 2015
      Replying to @CopperheadOS

      @CopperheadSec How do you propose 16-20 bits of entropy in a 20-bit page address space without rapid catastrophic fragmentation?

      7:41 PM - 19 Sep 2015
      1 reply 0 retweets 0 likes
        1. New conversation
        2. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @RichFelker

          @RichFelker It only randomizes the base, so it's a fixed cost. The cost of 16-bit entropy would be 256MiB of virtual memory with 4096 pages.

          1 reply 0 retweets 0 likes
        3. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @CopperheadOS

          @RichFelker Can then do a bit better (but it's hard to quantify) with fine-grained randomization within malloc, for secondary stacks, etc.

          1 reply 0 retweets 0 likes
        4. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @CopperheadOS

          @RichFelker I'd expect something like 16-bit on 32-bit and 17-bit for 32-bit processes with a 64-bit kernel.

          1 reply 0 retweets 0 likes
        5. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @CopperheadOS

          @RichFelker Saying "16-20" was silly since 20 is the whole address space for a 32-bit processes running on 64-bit. :P

          1 reply 0 retweets 0 likes
        6. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @CopperheadOS

          @RichFelker AFAIK, OpenBSD is the only OS doing fine-grained randomization for mmap beyond just the base address.

          1 reply 0 retweets 0 likes
        7. Rich Felker‏ @RichFelker 19 Sep 2015
          Replying to @CopperheadOS

          @CopperheadSec Userspace could emulate that just by mmap PROT_NONE with random size before each mmap, then munmapping it.

          1 reply 0 retweets 0 likes
        8. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @RichFelker

          @RichFelker That's essentially what CopperheadOS does for stacks but it keeps it around until unmapping: https://android-review.googlesource.com/#/c/161453/ 

          1 reply 0 retweets 0 likes
        9. CopperheadOS‏ @CopperheadOS 19 Sep 2015
          Replying to @CopperheadOS

          @RichFelker An attacker can overcome stuff like this via influence over heap allocations if reuse of the random gaps is allowed.

          1 reply 0 retweets 0 likes
        10. 2 more replies

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