From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752509AbdLLKXR (ORCPT ); Tue, 12 Dec 2017 05:23:17 -0500 Received: from mail-wr0-f193.google.com ([209.85.128.193]:33393 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752358AbdLLKXN (ORCPT ); Tue, 12 Dec 2017 05:23:13 -0500 X-Google-Smtp-Source: ACJfBotgaqFU73JOOAcyuZLcUX7Pio3hTpQP70rbuk4twmEikxaXyg39PKB3DPykwyIUExq6daM+hA== Date: Tue, 12 Dec 2017 11:23:10 +0100 From: Ingo Molnar To: Darren Hart Cc: LKML , Thomas Gleixner , Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH] futex: Check for uaddr alignment as early as possible Message-ID: <20171212102310.jp6jnw77x6d77rae@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Darren Hart wrote: > From: "Darren Hart (VMware)" > > uaddr alignment is currently tested by get_futex_key(). We can catch > misalignment earlier in sys_futex and return -EINVAL sooner. This > simplifies get_futex_key() a little, but more importantly exits the > kernel as soon as an invalid parameter is detected. > > Passes all selftests/futex testcases on a dual socket Xeon E5-2670, 16 > physical cores total, 32 threads total. > > Signed-off-by: Darren Hart (VMware) > Cc: Thomas Gleixner > Cc: Ingo Molnar > Cc: Peter Zijlstra > Cc: Darren Hart > --- > kernel/futex.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/futex.c b/kernel/futex.c > index 76ed592..c3ee6c4 100644 > --- a/kernel/futex.c > +++ b/kernel/futex.c > @@ -509,8 +509,6 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) > * The futex address must be "naturally" aligned. > */ > key->both.offset = address % PAGE_SIZE; > - if (unlikely((address % sizeof(u32)) != 0)) > - return -EINVAL; > address -= key->both.offset; > > if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) > @@ -3525,6 +3523,11 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, > u32 val2 = 0; > int cmd = op & FUTEX_CMD_MASK; > > + /* Only allow for aligned uaddr variables */ > + if (unlikely((unsigned long)uaddr % sizeof(u32) != 0 || > + (unsigned long)uaddr2 % sizeof(u32) != 0)) > + return -EINVAL; > + > if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || > cmd == FUTEX_WAIT_BITSET || > cmd == FUTEX_WAIT_REQUEUE_PI)) { Yeah, so I applied this yesterday, then -tip started regressing sporadically during distro networking bring-up, and it took me half a day of debugging to statistically bisect it back to this patch :-/ So it's apparently broken, but I don't see yet how. Thanks, Ingo