From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f174.google.com (mail-ig0-f174.google.com [209.85.213.174]) by kanga.kvack.org (Postfix) with ESMTP id 1D6476B0038 for ; Mon, 30 Nov 2015 20:00:36 -0500 (EST) Received: by igbxm8 with SMTP id xm8so86402492igb.1 for ; Mon, 30 Nov 2015 17:00:36 -0800 (PST) Received: from mail-ig0-x22a.google.com (mail-ig0-x22a.google.com. [2607:f8b0:4001:c05::22a]) by mx.google.com with ESMTPS id j15si3310378iod.139.2015.11.30.17.00.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 30 Nov 2015 17:00:35 -0800 (PST) Received: by igcmv3 with SMTP id mv3so83435439igc.0 for ; Mon, 30 Nov 2015 17:00:35 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20151130161811.592c205d8dc7b00f44066a37@linux-foundation.org> References: <1448578785-17656-1-git-send-email-dcashman@android.com> <1448578785-17656-2-git-send-email-dcashman@android.com> <20151130155412.b1a087f4f6f4d4180ab4472d@linux-foundation.org> <20151130160118.e43a2e53a59e347a95a94d5c@linux-foundation.org> <20151130161811.592c205d8dc7b00f44066a37@linux-foundation.org> Date: Mon, 30 Nov 2015 17:00:35 -0800 Message-ID: Subject: Re: [PATCH v4 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR. From: Kees Cook Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Daniel Cashman , LKML , Russell King - ARM Linux , Ingo Molnar , "linux-arm-kernel@lists.infradead.org" , Jonathan Corbet , Don Zickus , "Eric W. Biederman" , Heinrich Schuchardt , jpoimboe@redhat.com, "Kirill A. Shutemov" , n-horiguchi@ah.jp.nec.com, Andrea Arcangeli , Mel Gorman , Thomas Gleixner , David Rientjes , Linux-MM , "linux-doc@vger.kernel.org" , Mark Salyzyn , Jeffrey Vander Stoep , Nick Kralevich , Catalin Marinas , Will Deacon , "H. Peter Anvin" , "x86@kernel.org" , Hector Marco , Borislav Petkov , Daniel Cashman On Mon, Nov 30, 2015 at 4:18 PM, Andrew Morton wrote: > On Mon, 30 Nov 2015 16:04:36 -0800 Kees Cook wrote: > >> >> > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS >> >> > + { >> >> > + .procname = "mmap_rnd_bits", >> >> > + .data = &mmap_rnd_bits, >> >> > + .maxlen = sizeof(mmap_rnd_bits), >> >> > + .mode = 0600, >> >> > + .proc_handler = proc_dointvec_minmax, >> >> > + .extra1 = (void *) &mmap_rnd_bits_min, >> >> > + .extra2 = (void *) &mmap_rnd_bits_max, >> >> >> >> hm, why the typecasts? They're unneeded and are omitted everywhere(?) >> >> else in kernel/sysctl.c. >> > >> > Oh. Casting away constness. >> > >> > What's the thinking here? They can change at any time so they aren't >> > const so we shouldn't declare them to be const? >> >> The _min and _max values shouldn't be changing: they're decided based >> on the various CONFIG options that calculate the valid min/maxes. Only >> mmap_rnd_bits itself should be changing. > > hmpf. > > From: Andrew Morton > Subject: include/linux/sysctl.h: make ctl_table.extra1/2 const > > Nothing should be altering these values. Declare the pointed-to values to > be const so we can actually use const values. > > Cc: Kees Cook > Cc: Daniel Cashman > Signed-off-by: Andrew Morton > --- > > include/linux/sysctl.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff -puN include/linux/sysctl.h~a include/linux/sysctl.h > --- a/include/linux/sysctl.h~a > +++ a/include/linux/sysctl.h > @@ -111,8 +111,8 @@ struct ctl_table > struct ctl_table *child; /* Deprecated */ > proc_handler *proc_handler; /* Callback for text formatting */ > struct ctl_table_poll *poll; > - void *extra1; > - void *extra2; > + const void *extra1; > + const void *extra2; > }; > > struct ctl_node { > diff -puN kernel/sysctl.c~a kernel/sysctl.c > _ > If allyesconfig builds with this, I'm all for it. :) -Kees -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org