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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. Rich Felker‏ @RichFelker Apr 26
      Replying to @RichFelker @pikhq @whitequark

      For board-specific stuff, could run in virtualization/emu at runtime & subject it to normal mmu permissions.

      2 replies 0 retweets 1 like
    2.  🎃 unsafe { mem::transmute(@erincandescent) }  🎃‏ @erincandescent Apr 26
      Replying to @RichFelker @pikhq @whitequark

      Ok, what does this gain you? What do you do when your firmware crashes? What do you do when the firmware bricks itself (the set variable bug)?

      1 reply 0 retweets 1 like
    3. Rich Felker‏ @RichFelker Apr 26
      Replying to @erincandescent @pikhq @whitequark

      1. Immunity to buggy firmware introducing mem corruption or vulns. 2. Reset or disable the device. 3. Vars are all virtual; you can reset at every init.

      1 reply 0 retweets 0 likes
    4.  🎃 unsafe { mem::transmute(@erincandescent) }  🎃‏ @erincandescent Apr 26
      Replying to @RichFelker @pikhq @whitequark

      1. It can still trash various board level devices 2. Uh, what? How do you reset the firmware? (Answer: You reboot the PC) 3. This defeats the entire reason of writing firmware vars which is reconfiguring it and/or preserving data across boots

      1 reply 0 retweets 1 like
    5. Rich Felker‏ @RichFelker Apr 26
      Replying to @erincandescent @pikhq @whitequark

      1. Depends on what you allow it access to. 2. You run the virtualized reset code or use pm interfaces to hard power-cycle the specific device. 3. Yes, getting rid of statefullness is part of the point.

      1 reply 0 retweets 0 likes
    6. whitequark‏ @whitequark Apr 26
      Replying to @RichFelker @erincandescent @pikhq

      except, you know, I *want* to be able to adjust the boot options from within my OS

      3 replies 0 retweets 1 like
    7. Rich Felker‏ @RichFelker Apr 26
      Replying to @whitequark @erincandescent @pikhq

      That's reasonable, if it happens under the full control and authorization of the OS. It's not if it happens behind the OS's back through sketchy unseen and unreviewed code.

      2 replies 0 retweets 0 likes
    8.  🎃 unsafe { mem::transmute(@erincandescent) }  🎃‏ @erincandescent Apr 26
      Replying to @RichFelker @whitequark @pikhq

      It happens because the OS calls the SetVariable function which exists for this purpose

      1 reply 0 retweets 0 likes
    9. Rich Felker‏ @RichFelker Apr 26
      Replying to @erincandescent @whitequark @pikhq

      If you allow EFI code from system or peripheral firmware to run on the metal, it can happen any time they decide they want to. That's the problem. It should _only_ be possible when OS does it.

      1 reply 0 retweets 0 likes
    10.  🎃 unsafe { mem::transmute(@erincandescent) }  🎃‏ @erincandescent Apr 26
      Replying to @RichFelker @whitequark @pikhq

      No. It can only happen when the OS calls into said EFI code. Functions don't just call themselves

      1 reply 0 retweets 1 like
      Rich Felker‏ @RichFelker Apr 26
      Replying to @erincandescent @whitequark @pikhq

      Like when some hardware driver calls into firmware on the metal in ring0 with unrestricted memory access rather than actually implementing the functionality itself.

      4:28 PM - 26 Apr 2018
      1 reply 0 retweets 0 likes
        1. New conversation
        2.  🎃 unsafe { mem::transmute(@erincandescent) }  🎃‏ @erincandescent Apr 26
          Replying to @RichFelker @whitequark @pikhq

          The only times the kernel calls into UEFI are To exit boot services mode To ger/set firmware variables As a last ditch way of rebooting As a last ditch way of getting/setting the time (no RTC driver) To set wake from power off timers

          2 replies 0 retweets 0 likes
        3. Rich Felker‏ @RichFelker Apr 26
          Replying to @erincandescent @whitequark @pikhq

          That's a smaller set than I expected, but still much more than it should be, and would benefit from virtualization if the user wants any of that functionality.

          1 reply 0 retweets 0 likes
        4. Rich Felker‏ @RichFelker Apr 26
          Replying to @RichFelker @erincandescent and

          Fortunately there's always: # CONFIG_EFI is not set

          0 replies 0 retweets 0 likes
        5. End of conversation

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