From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755526Ab3COWSO (ORCPT ); Fri, 15 Mar 2013 18:18:14 -0400 Received: from mail-ob0-f180.google.com ([209.85.214.180]:59816 "EHLO mail-ob0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754890Ab3COWSN (ORCPT ); Fri, 15 Mar 2013 18:18:13 -0400 MIME-Version: 1.0 In-Reply-To: <5143990B.9000007@zytor.com> References: <20130215172143.12549.10292.stgit@localhost> <2012624.RMfkAO316Z@sifl> <1674827.FAh5HIjCC0@sifl> <5143990B.9000007@zytor.com> Date: Fri, 15 Mar 2013 15:18:12 -0700 Message-ID: Subject: Re: [PATCH] x86: remove the x32 syscall bitmask from syscall_get_nr() From: "H.J. Lu" To: "H. Peter Anvin" Cc: Paul Moore , x86@kernel.org, keescook@chromium.org, linux-kernel@vger.kernel.org, coreyb@linux.vnet.ibm.com, wad@chromium.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 15, 2013 at 2:56 PM, H. Peter Anvin wrote: > On 03/15/2013 02:15 PM, Paul Moore wrote: >> On Tuesday, February 26, 2013 03:58:23 PM Paul Moore wrote: >>> On Friday, February 15, 2013 12:21:43 PM Paul Moore wrote: >>>> Commit fca460f95e928bae373daa8295877b6905bc62b8 simplified the x32 >>>> implementation by creating a syscall bitmask, equal to 0x40000000, that >>>> could be applied to x32 syscalls such that the masked syscall number >>>> would be the same as a x86_64 syscall. While that patch was a nice >>>> way to simplify the code, it went a bit too far by adding the mask to >>>> syscall_get_nr(); returning the masked syscall numbers can cause >>>> confusion with callers that expect syscall numbers matching the x32 >>>> ABI, e.g. unmasked syscall numbers. >>>> >>>> This patch fixes this by simply removing the mask from syscall_get_nr() >>>> while preserving the other changes from the original commit. While >>>> there are several syscall_get_nr() callers in the kernel, most simply >>>> check that the syscall number is greater than zero, in this case this >>>> patch will have no effect. Of those remaining callers, they appear >>>> to be few, seccomp and ftrace, and from my testing of seccomp without >>>> this patch the original commit definitely breaks things; the seccomp >>>> filter does not correctly filter the syscalls due to the difference in >>>> syscall numbers in the BPF filter and the value from syscall_get_nr(). >>>> Applying this patch restores the seccomp BPF filter functionality on >>>> x32. >>>> >>>> I've tested this patch with the seccomp BPF filters as well as ftrace >>>> and everything looks reasonable to me; needless to say general usage >>>> seemed fine as well. >>> >>> I just wanted to check and see where things stood with this patch. I'm not >>> overly concerned about how this problem is solved, just that it is solved. >>> If someone else has a better approach that is fine with me; I'll even make >>> the offer to do additional testing if needed. >> >> Anyone? The seccomp filter bits are completely broken on x32 and I'd like to >> get this fixed, if not with this patch then something else - I'm more than >> happy to test/verify/etc whatever solution is deemed best ... >> > > Seems good to me -- H.J., do you seen any problem with this? > It looks OK to me. -- H.J.