From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752348AbdLLKXN (ORCPT ); Tue, 12 Dec 2017 05:23:13 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:32895 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751400AbdLLKXK (ORCPT ); Tue, 12 Dec 2017 05:23:10 -0500 Date: Tue, 12 Dec 2017 11:23:05 +0100 (CET) From: Thomas Gleixner To: Darren Hart cc: LKML , Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH] futex: Check for uaddr alignment as early as possible In-Reply-To: Message-ID: References: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 8 Dec 2017, 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)) Errm. How is that supposed to work? uaddr2 is not used by all opcodes..... Thanks, tglx