On 16 February 2018 at 10:55, Borislav Petkov <b...@alien8.de> wrote: > On Fri, Feb 16, 2018 at 10:41:45AM +0000, Ard Biesheuvel wrote: >> On 15 February 2018 at 18:22, Joe Konno <joe.ko...@linux.intel.com> wrote: >> > From: Joe Konno <joe.ko...@intel.com> >> > >> > It was pointed out that normal, unprivileged users reading certain EFI >> > variables (through efivarfs) can generate SMIs. Given these nodes are >> > created >> > with 0644 permissions, normal users could generate a lot of SMIs. By >> > restricting permissions a bit (patch 1), we can make it harder for normal >> > users >> > to generate spurious SMIs. >> > >> > A normal user could generate lots of SMIs by reading the efivarfs in a >> > trivial >> > loop: >> > >> > ``` >> > while true; do >> > cat /sys/firmware/efi/evivars/* > /dev/null >> > done >> > ``` >> > >> > Patch 1 in this series limits read and write permissions on efivarfs to the >> > owner/superuser. Group and world cannot access. >> > >> > Patch 2 is for consistency and hygiene. If we restrict permissions for >> > either >> > efivarfs or efi/vars, the other interface should get the same treatment. >> > >> >> I am inclined to apply this as a fix, but I will give the x86 guys a >> chance to respond as well. > > That stinking pile EFI never ceases to amaze me... > > Just one question: by narrowing permissions this way, aren't you > breaking some userspace which reads those? > > And if you do, then that's a no-no. > > Which then would mean that you'd have to come up with some caching > scheme to protect the firmware from itself. > > Or we could simply admit that EFI is a piece of crap, kill it and > start anew, this time much more conservatively and not add a whole OS > underneath the actual OS. >
By your own reasoning above, that's a no-no as well. But thanks for your input. Anyone else got something constructive to contribute?
