From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752707Ab3JZQFV (ORCPT ); Sat, 26 Oct 2013 12:05:21 -0400 Received: from mail.active-venture.com ([67.228.131.205]:61620 "EHLO mail.active-venture.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751615Ab3JZQFU (ORCPT ); Sat, 26 Oct 2013 12:05:20 -0400 X-Originating-IP: 108.223.40.66 Message-ID: <526BE835.2030608@roeck-us.net> Date: Sat, 26 Oct 2013 09:05:09 -0700 From: Guenter Roeck User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: Ingo Molnar , Jan Beulich CC: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com, arjan@linux.intel.com, linux-kernel@vger.kernel.org, Linus Torvalds , Andrew Morton , Peter Zijlstra Subject: Re: [PATCH 1/2] x86: unify copy_from_user() size checking References: <5265056D02000078000FC4F3@nat28.tlf.novell.com> <20131026103109.GC14949@gmail.com> In-Reply-To: <20131026103109.GC14949@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/26/2013 03:31 AM, Ingo Molnar wrote: > > * Jan Beulich wrote: > >> Commits 4a3127693001c61a21d1ce680db6340623f52e93 ("x86: Turn the >> copy_from_user check into an (optional) compile time warning") and >> 63312b6a6faae3f2e5577f2b001e3b504f10a2aa ("x86: Add a Kconfig option to >> turn the copy_from_user warnings into errors") touched only the 32-bit >> variant of copy_from_user(), whereas the original commit >> 9f0cf4adb6aa0bfccf675c938124e68f7f06349d ("x86: Use >> __builtin_object_size() to validate the buffer size for >> copy_from_user()") also added the same code to the 64-bit one. >> >> Further the earlier conversion from an inline WARN() to the call to >> copy_from_user_overflow() went a little too far: When the number of >> bytes to be copied is not a constant (e.g. [looking at 3.11] in >> drivers/net/tun.c:__tun_chr_ioctl() or >> drivers/pci/pcie/aer/aer_inject.c:aer_inject_write()), the compiler >> will always have to keep the funtion call, and hence there will always >> be a warning. By using __builtin_constant_p() we can avoid this. >> >> And then this slightly extends the effect of >> CONFIG_DEBUG_STRICT_USER_COPY_CHECKS in that apart from converting >> warnings to errors in the constant size case, it retains the (possibly >> wrong) warnings in the non-constant size case, such that if someone is >> prepared to get a few false positives, (s)he'll be able to recover the >> current behavior (except that these diagnostics now will never be >> converted to errors). >> >> Since the 32-bit variant (intentionally) didn't call might_fault(), the >> unification results in this being called twice now. Adding a suitable >> #ifdef would be the alternative if that's a problem. > > Addressing that sanely would be nice. > >> I'd like to point out though that with __compiletime_object_size() >> being restricted to gcc before 4.6, the whole construct is going to >> become more and more pointless going forward. I would question >> however that commit 2fb0815c9ee6b9ac50e15dd8360ec76d9fa46a2 ("gcc4: >> disable __compiletime_object_size for GCC 4.6+") was really necessary, >> and instead this should have been dealt with as is done here from the >> beginning. > > Can we now revert 2fb0815c9ee6? > I sure don't mind if there is a different and better solution. Guenter