Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751711AbdLAPel (ORCPT ); Fri, 1 Dec 2017 10:34:41 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:38012 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbdLAPek (ORCPT ); Fri, 1 Dec 2017 10:34:40 -0500 Date: Fri, 1 Dec 2017 15:34:44 +0000 From: Greg Kroah-Hartman To: Ard Biesheuvel Cc: Linus Torvalds , "Tobin C. Harding" , Matt Fleming , LKML , "linux-efi@vger.kernel.org" Subject: Re: [GIT PULL] hash addresses printed with %p Message-ID: <20171201153444.GA17867@kroah.com> References: <20171129045927.GA6217@eros> <20171129210848.GF6217@eros> <20171130163235.GA27849@kroah.com> <20171130171036.GB31817@kroah.com> <20171201094846.GE9353@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4688 Lines: 98 On Fri, Dec 01, 2017 at 09:54:43AM +0000, Ard Biesheuvel wrote: > On 1 December 2017 at 09:48, Greg Kroah-Hartman > wrote: > > On Thu, Nov 30, 2017 at 05:18:42PM +0000, Ard Biesheuvel wrote: > >> On 30 November 2017 at 17:10, Greg Kroah-Hartman > >> 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 > >> >> > 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. > > That's not what I said :-) > > These are real pointers, and stuff will actually be mapped there > (although I am not intimately familiar with the way x86 does this, but > on ARM [which does not have these sysfs nodes in the first place], > these mappings are only live during the time a UEFI runtime service > call is in progress, and IIRC, work was underway to do the same for > x86). So while these values don't correlate with the placement of > kernel data structures, they could still be useful for an attacker to > figure out where exploitable firmware memory regions are located, > especially given that some of these may be mapped RWX. Ah, ok, then yes, make that file readable from root only. And isn't there a specific %p modifier you should use for a kernel pointer. I've lost the thread here for what should, or should not, be done for kernel pointers these days based on the long email discussion. thanks, greg k-h