From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-f200.google.com (mail-oi1-f200.google.com [209.85.167.200]) by kanga.kvack.org (Postfix) with ESMTP id E1CDB6B6F85 for ; Tue, 4 Dec 2018 11:02:46 -0500 (EST) Received: by mail-oi1-f200.google.com with SMTP id b18so10647715oii.1 for ; Tue, 04 Dec 2018 08:02:46 -0800 (PST) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id 96si7428378otq.153.2018.12.04.08.02.45 for ; Tue, 04 Dec 2018 08:02:45 -0800 (PST) Date: Tue, 4 Dec 2018 16:03:04 +0000 From: Will Deacon Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages Message-ID: <20181204160304.GB7195@arm.com> References: <20181128000754.18056-1-rick.p.edgecombe@intel.com> <20181128000754.18056-2-rick.p.edgecombe@intel.com> <4883FED1-D0EC-41B0-A90F-1A697756D41D@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4883FED1-D0EC-41B0-A90F-1A697756D41D@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Nadav Amit Cc: Rick Edgecombe , Andrew Morton , Andy Lutomirski , linux-mm , LKML , Kernel Hardening , naveen.n.rao@linux.vnet.ibm.com, anil.s.keshavamurthy@intel.com, David Miller , Masami Hiramatsu , Steven Rostedt , Ingo Molnar , ast@kernel.org, Daniel Borkmann , jeyu@kernel.org, netdev@vger.kernel.org, Ard Biesheuvel , Jann Horn , kristen@linux.intel.com, Dave Hansen , deneen.t.dock@intel.com, Peter Zijlstra On Mon, Dec 03, 2018 at 05:43:11PM -0800, Nadav Amit wrote: > > On Nov 27, 2018, at 4:07 PM, Rick Edgecombe wrote: > > > > Since vfree will lazily flush the TLB, but not lazily free the underlying pages, > > it often leaves stale TLB entries to freed pages that could get re-used. This is > > undesirable for cases where the memory being freed has special permissions such > > as executable. > > So I am trying to finish my patch-set for preventing transient W+X mappings > from taking space, by handling kprobes & ftrace that I missed (thanks again for > pointing it out). > > But all of the sudden, I don’t understand why we have the problem that this > (your) patch-set deals with at all. We already change the mappings to make > the memory writable before freeing the memory, so why can’t we make it > non-executable at the same time? Actually, why do we make the module memory, > including its data executable before freeing it??? Yeah, this is really confusing, but I have a suspicion it's a combination of the various different configurations and hysterical raisins. We can't rely on module_alloc() allocating from the vmalloc area (see nios2) nor can we rely on disable_ro_nx() being available at build time. If we *could* rely on module allocations always using vmalloc(), then we could pass in Rick's new flag and drop disable_ro_nx() altogether afaict -- who cares about the memory attributes of a mapping that's about to disappear anyway? Is it just nios2 that does something different? Will