From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Paris Subject: Re: [PATCH 2/3] [RFC] seccomp: give BPF x32 bit when restoring x32 filter Date: Fri, 11 Jul 2014 12:16:47 -0400 Message-ID: <1405095407.2357.1.camel@flatline.rdu.redhat.com> References: <6a69eb94b4cfac5f94b229c2eb2ebc402aac722a.1405023592.git.rgb@redhat.com> <53BF62AA.20105@zytor.com> <1458762.ra4TnS54ZN@sifl> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1458762.ra4TnS54ZN@sifl> Sender: linux-kernel-owner@vger.kernel.org To: Paul Moore Cc: "H. Peter Anvin" , Richard Guy Briggs , linux-audit@redhat.com, linux-kernel@vger.kernel.org, Al Viro , Will Drewry List-Id: linux-audit@redhat.com On Fri, 2014-07-11 at 12:11 -0400, Paul Moore wrote: > On Thursday, July 10, 2014 09:06:02 PM H. Peter Anvin wrote: > > Incidentally: do seccomp users know that on an x86-64 system you can > > recevie system calls from any of the x86 architectures, regardless of > > how the program is invoked? (This is unusual, so normally denying those > > "alien" calls is the right thing to do.) > > I obviously can't speak for all seccomp users, but libseccomp handles this by > checking the seccomp_data->arch value at the start of the filter and killing > (by default) any non-native architectures. If you want, you can change this > default behavior or add support for other architectures (e.g. create a filter > that allows both x86-64 and x32 but disallows x86, or any combination of the > three for that matter). Maybe libseccomp does some HORRIFIC contortions under the hood, but the interface is crap... Since seccomp_data->arch can't distinguish between X32 and X86_64. If I write a seccomp filter which says KILL arch != x86_64 KILL init_module ALLOW everything else I can still call init_module, I just have to use the X32 variant. If libseccomp is translating: KILL arch != x86_64 into: KILL arch != x86_64 KILL syscall_nr >= 2000 That's just showing how dumb the kernel interface is... Good for you guys, but the kernel is just being dumb :)