From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id E90946B0005 for ; Mon, 5 Mar 2018 11:23:50 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id u188so9962233pfb.6 for ; Mon, 05 Mar 2018 08:23:50 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id l61-v6si9535519plb.95.2018.03.05.08.23.49 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 05 Mar 2018 08:23:49 -0800 (PST) Date: Mon, 5 Mar 2018 08:23:43 -0800 From: Matthew Wilcox Subject: Re: [RFC PATCH] Randomization of address chosen by mmap. Message-ID: <20180305162343.GA8230@bombadil.infradead.org> References: <20180227131338.3699-1-blackzert@gmail.com> <55C92196-5398-4C19-B7A7-6C122CD78F32@gmail.com> <20180228183349.GA16336@bombadil.infradead.org> <2CF957C6-53F2-4B00-920F-245BEF3CA1F6@gmail.com> <20180304034704.GB20725@bombadil.infradead.org> <20180304205614.GC23816@bombadil.infradead.org> <7FA6631B-951F-42F4-A7BF-8E5BB734D709@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7FA6631B-951F-42F4-A7BF-8E5BB734D709@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Ilya Smith Cc: Daniel Micay , Kees Cook , Andrew Morton , Dan Williams , Michal Hocko , "Kirill A. Shutemov" , Jan Kara , Jerome Glisse , Hugh Dickins , Helge Deller , Andrea Arcangeli , Oleg Nesterov , Linux-MM , LKML , Kernel Hardening On Mon, Mar 05, 2018 at 04:09:31PM +0300, Ilya Smith wrote: > > On 4 Mar 2018, at 23:56, Matthew Wilcox wrote: > > Thinking about this more ... > > > > - When you call munmap, if you pass in the same (addr, length) that were > > used for mmap, then it should unmap the guard pages as well (that > > wasn't part of the patch, so it would have to be added) > > - If 'addr' is higher than the mapped address, and length at least > > reaches the end of the mapping, then I would expect the guard pages to > > "move down" and be after the end of the newly-shortened mapping. > > - If 'addr' is higher than the mapped address, and the length doesn't > > reach the end of the old mapping, we split the old mapping into two. > > I would expect the guard pages to apply to both mappings, insofar as > > they'll fit. For an example, suppose we have a five-page mapping with > > two guard pages (MMMMMGG), and then we unmap the fourth page. Now we > > have a three-page mapping with one guard page followed immediately > > by a one-page mapping with two guard pages (MMMGMGG). > > Ia??m analysing that approach and see much more problems: > - each time you call mmap like this, you still increase count of vmas as my > patch did Umm ... yes, each time you call mmap, you get a VMA. I'm not sure why that's a problem with my patch. I was trying to solve the problem Daniel pointed out, that mapping a guard region after each mmap cost twice as many VMAs, and it solves that problem. > - now feature vma_merge shouldna??t work at all, until MAP_FIXED is set or > PROT_GUARD(0) That's true. > - the entropy you provide is like 16 bit, that is really not so hard to brute It's 16 bits per mapping. I think that'll make enough attacks harder to be worthwhile. > - in your patch you dona??t use vm_guard at address searching, I see many roots > of bugs here Don't need to. vm_end includes the guard pages. > - if you unmap/remap one page inside region, field vma_guard will show head > or tail pages for vma, not both; kernel dona??t know how to handle it There are no head pages. The guard pages are only placed after the real end. > - user mode now choose entropy with PROT_GUARD macro, where did he gets it? > User mode shouldna??t be responsible for entropy at all I can't agree with that. The user has plenty of opportunities to get randomness; from /dev/random is the easiest, but you could also do timing attacks on your own cachelines, for example. -- 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