From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934692AbeBPK6u (ORCPT ); Fri, 16 Feb 2018 05:58:50 -0500 Received: from mail-io0-f172.google.com ([209.85.223.172]:35991 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934609AbeBPK6s (ORCPT ); Fri, 16 Feb 2018 05:58:48 -0500 X-Google-Smtp-Source: AH8x225JmvkheiFjL7P4AhzA3SBaCqyvHmXQ1EK4sOhVJNCyclzvPafBPbJZu2oGY0/ArtZ1/A7DNFsLiMudXbQP0bU= MIME-Version: 1.0 In-Reply-To: <20180216105548.GA29042@pd.tnic> References: <20180215182208.35003-1-joe.konno@linux.intel.com> <20180216105548.GA29042@pd.tnic> From: Ard Biesheuvel Date: Fri, 16 Feb 2018 10:58:47 +0000 Message-ID: Subject: Re: [PATCH 0/2] efivars: reading variables can generate SMIs To: Borislav Petkov Cc: Joe Konno , Matthew Garrett , Ingo Molnar , Andy Lutomirski , linux-efi@vger.kernel.org, Linux Kernel Mailing List , Jeremy Kerr , Andi Kleen , Tony Luck , Benjamin Drung , Peter Jones Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16 February 2018 at 10:55, Borislav Petkov wrote: > On Fri, Feb 16, 2018 at 10:41:45AM +0000, Ard Biesheuvel wrote: >> On 15 February 2018 at 18:22, Joe Konno wrote: >> > From: Joe Konno >> > >> > 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?