Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754732Ab3JBRUi (ORCPT ); Wed, 2 Oct 2013 13:20:38 -0400 Received: from mail-qa0-f54.google.com ([209.85.216.54]:56964 "EHLO mail-qa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754150Ab3JBRUa (ORCPT ); Wed, 2 Oct 2013 13:20:30 -0400 MIME-Version: 1.0 In-Reply-To: References: <20130930165420.GI3081@twins.programming.kicks-ass.net> <20131002112316.GP3081@twins.programming.kicks-ass.net> <20131002115826.GM26785@twins.programming.kicks-ass.net> <20131002123953.GB27811@gmail.com> <20131002124610.GD28601@twins.programming.kicks-ass.net> <20131002130143.GF28601@twins.programming.kicks-ass.net> <20131002133759.GH28601@twins.programming.kicks-ass.net> Date: Wed, 2 Oct 2013 19:20:28 +0200 Message-ID: Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions From: Stephane Eranian To: Kees Cook Cc: Peter Zijlstra , Ingo Molnar , LKML , "mingo@elte.hu" , "ak@linux.intel.com" , Arnaldo Carvalho de Melo , David Ahern , Jiri Olsa , Hugh Dickins , Linus Torvalds , Andrew Morton Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3199 Lines: 66 On Wed, Oct 2, 2013 at 7:14 PM, Kees Cook wrote: > On Wed, Oct 2, 2013 at 6:37 AM, Peter Zijlstra wrote: >> On Wed, Oct 02, 2013 at 03:13:16PM +0200, Stephane Eranian wrote: >>> On Wed, Oct 2, 2013 at 3:01 PM, Peter Zijlstra wrote: >>> > On Wed, Oct 02, 2013 at 02:59:32PM +0200, Stephane Eranian wrote: >>> >> On Wed, Oct 2, 2013 at 2:46 PM, Peter Zijlstra wrote: >>> >> > On Wed, Oct 02, 2013 at 02:39:53PM +0200, Ingo Molnar wrote: >>> >> >> - then there are timing attacks, and someone having access to a PMU >>> >> >> context and who can trigger this SHA1 computation arbitrarily in task >>> >> >> local context can run very accurate and low noise timing attacks... >>> >> >> >>> >> >> I don't think the kernel's sha_transform() is hardened against timing >>> >> >> attacks, it's performance optimized so it has variable execution time >>> >> >> highly dependent on plaintext input - which leaks information about the >>> >> >> plaintext. >>> >> > >>> >> > Typical user doesn't have enough priv to profile kernel space; once you >>> >> > do you also have enough priv to see kernel addresses outright (ie. >>> >> > kallsyms etc..). >>> >> > >>> >> I was going to say just that. But that's not the default, paranoid level >>> >> is at 1 by default and not 2. So I supposedly can still do: >>> >> >>> >> $ perf record -e cycles ...... >>> >> >>> >> In per-thread mode and collect kernel level addresses. >>> > >>> > Oh right you are.. so yes that's a very viable avenue. >>> >>> You mean simply encoding the vma->vm_mm as the ino number, for instance. >> >> Nah.. I think Kees would very much shoot us on the spot for doing that. >> But with the paranoid level defaulting to 1 the PMU attack on the kernel >> SHA implenentation is feasible. > > We already have other kernel address leaks (e.g. heap addresses via > INET_DIAG), and I'd like to avoid adding more. It'd be nice if there > was a common way to uniquely mask these values that are really just > "handles". We could use it both here and in the network code. > > Would it be possible to just have a "regular" incrementing handle, > like fd, or are we talking about doing that map for all VMAs, which > would make that mapping unfeasible due to storage needs? > All we need is a way to report that two vmas point to the same vma->vm_mm, i..e, same physical data. If I understand what you are suggesting, you'd add some sort of generation number to the vm_mm. Each new vm_mm gets a new number. That would work, I think. No kernel addresses reported directly nor hashed. > On the other hand, trying to hide kernel addresses from root is no > easy task, especially given that while kptr_restrict has a "2" level, > dmesg_restrict does not. Are these kernel-address-leaking perf modes > already limited to a specific POSIX capability? > > -Kees > > -- > Kees Cook > Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/