From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f170.google.com (mail-pd0-f170.google.com [209.85.192.170]) by kanga.kvack.org (Postfix) with ESMTP id 418AA6B0038 for ; Wed, 18 Mar 2015 10:12:08 -0400 (EDT) Received: by pdbni2 with SMTP id ni2so44377494pdb.1 for ; Wed, 18 Mar 2015 07:12:08 -0700 (PDT) Received: from mga09.intel.com (mga09.intel.com. [134.134.136.24]) by mx.google.com with ESMTP id xx7si36296455pab.72.2015.03.18.07.12.07 for ; Wed, 18 Mar 2015 07:12:07 -0700 (PDT) Message-ID: <550987AD.8020409@intel.com> Date: Wed, 18 Mar 2015 07:11:57 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [PATCH RFC] mm: protect suid binaries against rowhammer with copy-on-read mappings References: <20150318083040.7838.76933.stgit@zurg> In-Reply-To: <20150318083040.7838.76933.stgit@zurg> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Cc: Andrew Morton , Linus Torvalds , Andy Lutomirski On 03/18/2015 01:30 AM, Konstantin Khlebnikov wrote: > + /* > + * Read-only SUID/SGID binares are mapped as copy-on-read > + * this protects them against exploiting with Rowhammer. > + */ > + if (!(file->f_mode & FMODE_WRITE) && > + ((inode->i_mode & S_ISUID) || ((inode->i_mode & S_ISGID) && > + (inode->i_mode & S_IXGRP)))) { > + vm_flags &= ~(VM_SHARED | VM_MAYSHARE); > + vm_flags |= VM_COR; > + } I think we probably need to come to _some_ sort of understanding in the kernel of how much we are willing to do to thwart these kinds of attacks. I suspect it's a very deep rabbit hole. For this particular case, I don't see how this would be effective. The existing exploit which you reference attacks PTE pages which are unmapped in to the user address space. I'm confused how avoiding mapping a page in to an attacker's process can keep it from being exploited. Right now, there's a relatively small number of pages that will get COW'd for a SUID binary. This greatly increases the number which could allow spraying of these (valuable) copy-on-read pages. -- 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