On Thu, Nov 30, 2017 at 05:18:42PM +0000, Ard Biesheuvel wrote: > On 30 November 2017 at 17:10, Greg Kroah-Hartman > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Nov 30, 2017 at 04:32:35PM +0000, Greg Kroah-Hartman wrote: > >> On Wed, Nov 29, 2017 at 01:36:25PM -0800, Linus Torvalds wrote: > >> > On Wed, Nov 29, 2017 at 1:14 PM, Linus Torvalds > >> > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > >> > > > >> > > Not because %pK itself changed, but because the semantics of %p did. > >> > > The baseline moved, and the "safe" version did not. > >> > > >> > Btw, that baseline for me is now that I can do > >> > > >> > ./scripts/leaking_addresses.pl | wc -l > >> > 18 > >> > > >> > and of those 18 hits, six are false positives (looks like bitmaps in > >> > the uevent keys). > >> > > >> > The remaining 12 are from the EFI runtime map files > >> > (/sys/firmware/efi/runtime-map/*). They should presumably not be > >> > world-readable, but sadly the kset_create_and_add() helper seems to do > >> > that by default. > >> > > >> > I think the sysfs code makes it insanely too easy to make things > >> > world-readable. You try to be careful, and mark things read-only etc, > >> > but __ATTR_RO() jkust means S_IRUGO, which means world-readable. > >> > > >> > There seems to be no convenient model for kobjects having better > >> > permissions. Greg? > >> > >> They can just use __ATTR() which lets you set the exact mode settings > >> that are wanted. > >> > >> Something like the patch below, which breaks the build as the > >> map_attributes are "odd", but you get the idea. The EFI developers can > >> fix this up properly :) > >> > >> Note, this only accounts for 5 attributes, what is the whole list? > > > > Ah, it's the virt_addr file 12 times, I just ran it on my laptop: > > > > /sys/firmware/efi/runtime-map/7/virt_addr: 0xfffffffeea6ea000 > > /sys/firmware/efi/runtime-map/5/virt_addr: 0xfffffffeee88b000 > > /sys/firmware/efi/runtime-map/3/virt_addr: 0xfffffffefea00000 > > /sys/firmware/efi/runtime-map/11/virt_addr: 0xfffffffed9c00000 > > /sys/firmware/efi/runtime-map/1/virt_addr: 0xfffffffefee00000 > > /sys/firmware/efi/runtime-map/8/virt_addr: 0xfffffffedba4e000 > > /sys/firmware/efi/runtime-map/6/virt_addr: 0xfffffffeee2de000 > > /sys/firmware/efi/runtime-map/4/virt_addr: 0xfffffffeeea00000 > > /sys/firmware/efi/runtime-map/2/virt_addr: 0xfffffffefec00000 > > /sys/firmware/efi/runtime-map/10/virt_addr: 0xfffffffed9c60000 > > /sys/firmware/efi/runtime-map/0/virt_addr: 0xfffffffeff000000 > > /sys/firmware/efi/runtime-map/9/virt_addr: 0xfffffffedb9c9000 > > > > So changing it to use __ATTR() should fix this remaning leakage up. > > That is if we even really need to export these values at all. What does > > userspace do with them? Shouldn't they just be in debugfs instead? > > > > These are the virtual mappings UEFI firmware regions, which must > remain in the same place across kexec reboots. So kexec tooling > consumes this information and passes it on to the incoming kernel in > some way. > > Note that these are not kernel addresses, so while I agree they should > not be world readable, they won't give you any clue as to where the > kernel itself is mapped. > > So the recommendation is to switch to __ATTR( ... 0400 ... ) instead? > If so, I'll code up a patch. If these pointers are not "real", I recommend just leaving them as-is. But perhaps put a comment in the file saying that, so the next time we run across them in a few years, we don't freak out and worry :) thanks, greg k-h -- 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
