On 21 November 2016 at 20:05, Peter Jones <pjones@xxxxxxxxxx> wrote: > On Mon, Nov 21, 2016 at 04:42:45PM +0000, Ard Biesheuvel wrote: >> On 21 November 2016 at 16:26, Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote: >> > On Mon, Nov 21, 2016 at 11:18 AM, Ard Biesheuvel >> > <ard.biesheuvel@xxxxxxxxxx> wrote: >> >> On 16 November 2016 at 18:11, David Howells <dhowells@xxxxxxxxxx> wrote: >> >>> From: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> >> >>> >> >>> If a user tells shim to not use the certs/hashes in the UEFI db variable >> >>> for verification purposes, shim will set a UEFI variable called >> >>> MokIgnoreDB. Have the uefi import code look for this and ignore the db >> >>> variable if it is found. >> >>> >> >> >> >> Similar concern as in the previous patch: it appears to me that you >> >> can DoS a machine by setting MokIgnoreDB if, e.g., its modules are >> >> signed against a cert that resides in db, and shim/mokmanager are not >> >> being used. >> > >> > If shim/mokmanager aren't used, then you can't actually modify >> > MokIgnoreDB. Again, it requires physical access and a reboot into >> > mokmanager to actually take effect. >> > >> >> This does the trick as well >> >> printf "\x07\x00\x00\x00\x01" > >> /sys/firmware/efi/efivars/MokIgnoreDB-605dab50-e046-4300-abb6-3dd810dd8b23 > > So that really means two things. First, kernel should only honor any of > the Mok* variables if they're Boot Services-only variables. Second, to > avoid the DoS, shim should create them all as Boot Services-only the > first time it boots. That'll prevent them from being created post-boot. > All of that assumes you are using shim and mokmanager in the first place. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
