From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH v2 4/5] mm: introduce MADV_PAGEOUT Date: Thu, 20 Jun 2019 11:22:09 +0200 Message-ID: <20190620092209.GD12083@dhcp22.suse.cz> References: <20190610111252.239156-1-minchan@kernel.org> <20190610111252.239156-5-minchan@kernel.org> <20190619132450.GQ2968@dhcp22.suse.cz> <20190620041620.GB105727@google.com> <20190620070444.GB12083@dhcp22.suse.cz> <20190620084040.GD105727@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190620084040.GD105727@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Minchan Kim Cc: Andrew Morton , linux-mm , LKML , linux-api@vger.kernel.org, Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon , jannh@google.com, oleg@redhat.com, christian@brauner.io, oleksandr@redhat.com, hdanton@sina.com, lizeb@google.com List-Id: linux-api@vger.kernel.org On Thu 20-06-19 17:40:40, Minchan Kim wrote: > > > > Pushing out a shared page cache > > > > is possible even now but this interface gives a much easier tool to > > > > evict shared state and perform all sorts of timing attacks. Unless I am > > > > missing something we should be doing something similar to mincore and > > > > ignore shared pages without a writeable access or at least document why > > > > we do not care. > > > > > > I'm not sure IIUC side channel attach. As you mentioned, without this syscall, > > > 1. they already can do that simply by memory hogging > > > > This is way much more harder for practical attacks because the reclaim > > logic is not fully under the attackers control. Having a direct tool to > > reclaim memory directly then just opens doors to measure the other > > consumers of that memory and all sorts of side channel. > > Not sure it's much more harder. It's really easy on my experience. > Just creating new memory hogger and consume memory step by step until > you newly allocated pages will be reclaimed. You can contain an untrusted application into a memcg and it will only reclaim its own working set. > > > 2. If we need fix MADV_PAGEOUT, that means we need to fix MADV_DONTNEED, too? > > > > nope because MADV_DONTNEED doesn't unmap from other processes. > > Hmm, I don't understand. MADV_PAGEOUT doesn't unmap from other > processes, either. Either I am confused or missing something. shrink_page_list does try_to_unmap and that unmaps from all processes, right? > Could you elborate it a bit more what's your concern? If you manage to unmap from a remote process then you can measure delays implied from the refault and that information can be used to infer what the remote application is doing. -- Michal Hocko SUSE Labs