3 ms·

You could also unenroll all vendor supplied signing keys and load it up with one that you keep in a HSM. Yes, you are technically correct that any opportunisti

You could also unenroll all vendor supplied signing keys and load it up with one that you keep in a HSM. Yes, you are technically correct that any opportunistic encryption scheme can be bypassed but it adds cost to the attack and (more importantly) it is a step towards a more secure system.

poizan42 9y ago
I feel like that is missing the point. You need social engineering (and probably not an easy case) to get people to change the keys. Using a pre-made image that allows you to bypass secure boot by way of a windows driver with a known vuln is practically free as soon as anyone packages it. I don't know whether that is currently being done, but I suspect it since I have seen people discussing bypassing PatchGuard in Windows 10 where they used a known exploit in a driver from a company that starts with n and ends with vidia.
- my123 9y ago
  PatchGuard can be disarmed on 8.1 ;-)
zokier 9y ago
I remember hearing that there is some problem unenrolling vendor keys, especially MS ones, because they are also used to sign some of the firmware blobs. I'm not sure if that concern really became realized at any point, do you have any information regarding that?
- my123 9y ago
  Blobs inside the FW image are not subjected to signature checks.
  - zokier 9y ago
    I think it is bit more complicated than that. I checked some presentations [1] about UEFI/SB, and they do seem to imply that there is potentially some blobs (namely option roms, uefi applications and dxe drivers) that need to pass signature check. I don't know how much such modularity is really used in real life, especially in the boot path, but I think the "best practice" recommendation is to keep dxe core small and have stuff as loadable drivers. [1] eg http://c7zero.info/stuff/Windows8SecureBoot_Bulygin-Furtak-Bazhniuk_BHUSA2013.pdf http://c7zero.info/stuff/Windows8SecureBoot_Bulygin-Furtak-B...
    - my123 9y ago
      Everything that is in the ROM proper isn't checked actually, in TianoCore at least.
hedora 9y ago
I think I set this up in about 5 minutes on my devuan laptop (basically just Debian 8.3 for the purposes of this discussion). I told it to delete all its keys, then whitelisted the debian efi blob (no Microsoft signature needed), and all was well. I did not test the configuration with an old copy of windows, but I'm pretty sure installing secure-boot enabled Linux distros now fails as expected. Is this not standard functionality for secureboot laptops?

poizan42 9y ago

I feel like that is missing the point. You need social engineering (and probably not an easy case) to get people to change the keys. Using a pre-made image that allows you to bypass secure boot by way of a windows driver with a known vuln is practically free as soon as anyone packages it. I don't know whether that is currently being done, but I suspect it since I have seen people discussing bypassing PatchGuard in Windows 10 where they used a known exploit in a driver from a company that starts with n and ends with vidia.

my123 9y ago
PatchGuard can be disarmed on 8.1 ;-)

zokier 9y ago

I remember hearing that there is some problem unenrolling vendor keys, especially MS ones, because they are also used to sign some of the firmware blobs. I'm not sure if that concern really became realized at any point, do you have any information regarding that?

my123 9y ago
Blobs inside the FW image are not subjected to signature checks.
- zokier 9y ago
  I think it is bit more complicated than that. I checked some presentations [1] about UEFI/SB, and they do seem to imply that there is potentially some blobs (namely option roms, uefi applications and dxe drivers) that need to pass signature check. I don't know how much such modularity is really used in real life, especially in the boot path, but I think the "best practice" recommendation is to keep dxe core small and have stuff as loadable drivers. [1] eg http://c7zero.info/stuff/Windows8SecureBoot_Bulygin-Furtak-Bazhniuk_BHUSA2013.pdf http://c7zero.info/stuff/Windows8SecureBoot_Bulygin-Furtak-B...
  - my123 9y ago
    Everything that is in the ROM proper isn't checked actually, in TianoCore at least.

hedora 9y ago

I think I set this up in about 5 minutes on my devuan laptop (basically just Debian 8.3 for the purposes of this discussion). I told it to delete all its keys, then whitelisted the debian efi blob (no Microsoft signature needed), and all was well. I did not test the configuration with an old copy of windows, but I'm pretty sure installing secure-boot enabled Linux distros now fails as expected. Is this not standard functionality for secureboot laptops?