From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:53783 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754457AbbIKWtV (ORCPT ); Fri, 11 Sep 2015 18:49:21 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "David S. Miller" , Anton Blanchard , Benjamin Herrenschmidt , Will Deacon , Dan McGee , Yann Droneaud , Matthias Brugger Subject: [PATCH 3.10 11/11] arm64/mm: Remove hack in mmap randomize layout Date: Fri, 11 Sep 2015 15:49:10 -0700 Message-Id: <20150911224528.994893179@linuxfoundation.org> In-Reply-To: <20150911224528.501106420@linuxfoundation.org> References: <20150911224528.501106420@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: stable-owner@vger.kernel.org List-ID: 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yann Droneaud commit d6c763afab142a85e4770b4bc2a5f40f256d5c5d upstream. Since commit 8a0a9bd4db63 ('random: make get_random_int() more random'), get_random_int() returns a random value for each call, so comment and hack introduced in mmap_rnd() as part of commit 1d18c47c735e ('arm64: MMU fault handling and page table management') are incorrects. Commit 1d18c47c735e seems to use the same hack introduced by commit a5adc91a4b44 ('powerpc: Ensure random space between stack and mmaps'), latter copied in commit 5a0efea09f42 ('sparc64: Sharpen address space randomization calculations.'). But both architectures were cleaned up as part of commit fa8cbaaf5a68 ('powerpc+sparc64/mm: Remove hack in mmap randomize layout') as hack is no more needed since commit 8a0a9bd4db63. So the present patch removes the comment and the hack around get_random_int() on AArch64's mmap_rnd(). Cc: David S. Miller Cc: Anton Blanchard Cc: Benjamin Herrenschmidt Acked-by: Will Deacon Acked-by: Dan McGee Signed-off-by: Yann Droneaud Signed-off-by: Will Deacon Cc: Matthias Brugger Signed-off-by: Greg Kroah-Hartman --- arch/arm64/mm/mmap.c | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -47,22 +47,14 @@ static int mmap_is_legacy(void) return sysctl_legacy_va_layout; } -/* - * Since get_random_int() returns the same value within a 1 jiffy window, we - * will almost always get the same randomisation for the stack and mmap - * region. This will mean the relative distance between stack and mmap will be - * the same. - * - * To avoid this we can shift the randomness by 1 bit. - */ static unsigned long mmap_rnd(void) { unsigned long rnd = 0; if (current->flags & PF_RANDOMIZE) - rnd = (long)get_random_int() & (STACK_RND_MASK >> 1); + rnd = (long)get_random_int() & STACK_RND_MASK; - return rnd << (PAGE_SHIFT + 1); + return rnd << PAGE_SHIFT; } static unsigned long mmap_base(void)