From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B0145C04EB8 for ; Thu, 6 Dec 2018 07:29:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6493A2146D for ; Thu, 6 Dec 2018 07:29:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="DOZnn/M+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6493A2146D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729170AbeLFH3R (ORCPT ); Thu, 6 Dec 2018 02:29:17 -0500 Received: from mail-it1-f194.google.com ([209.85.166.194]:36450 "EHLO mail-it1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728909AbeLFH3Q (ORCPT ); Thu, 6 Dec 2018 02:29:16 -0500 Received: by mail-it1-f194.google.com with SMTP id c9so24407755itj.1 for ; Wed, 05 Dec 2018 23:29:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=w851g1bWXN2LUEbHju2BffnaiL1F6iTfDSMuWX7q/d4=; b=DOZnn/M+qHdWqMt9L+MFyKosGzGi8ZbkO77eitas9/wBe/OJGPGdWdn4FdbccUheil NK6Def05O7NmSiBwwAmbsDWJodHhA7mm4ZcsTwluuD1BfnSKmxG1CbyHr0LfmIPYj7x8 dol+IjF+NAKzKABfVkAOLcTEq+f6YblUfwatU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=w851g1bWXN2LUEbHju2BffnaiL1F6iTfDSMuWX7q/d4=; b=tqW/gJnhP/e1lnmb/8qFT1LDeh4deJLsV/Aq9Akaq3Jqb0qrS2bGP5xjGeAXkcGARI +mxByEYm1Grp3xFmWZQ8WDHaSqn563iGfO8eSu5L/3RCO5jWiDx5J1sEGzkStBWCyHvG kJ3nH5GGtTgbcBuc9fc/TXoG6SxeFwHntjFDVu5kkAHikUwkdU5kOsamCiVi1EJ4X0Iz 6/HuXujqOZiB1f18QDxYUeWE3qhmRQ/eqkuhyXLgUZLDxp+5IkdVLSaB0K6H7z/oDDMr z2RWfS50DUChTttL6tqm428nt87wZJHAbdnJfF8fTckffXXjPIu8a7syV0dvPPzBWTTN fsSw== X-Gm-Message-State: AA+aEWbtBo9gsuSRVTHbh0BAGl8tcVkyS0C2e0HSWgQW8JeiEORQuIyY fNDC1I2FJ2j31Q07z1OslkNBxmKnaWwMrDJGqj2G3Q== X-Google-Smtp-Source: AFSGD/U38WuqH43qneRJAxsz1YRs+ODsCuPCuyComJIs46IPFwSbbLUzBgdJVQy8GwPCEtW9suAOCyyx3DeVKFWud6k= X-Received: by 2002:a02:4c9:: with SMTP id 192mr24778227jab.2.1544081355010; Wed, 05 Dec 2018 23:29:15 -0800 (PST) MIME-Version: 1.0 References: <20181128000754.18056-1-rick.p.edgecombe@intel.com> <20181128000754.18056-2-rick.p.edgecombe@intel.com> <4883FED1-D0EC-41B0-A90F-1A697756D41D@gmail.com> <20181204160304.GB7195@arm.com> <51281e69a3722014f718a6840f43b2e6773eed90.camel@intel.com> <20181205114148.GA15160@arm.com> In-Reply-To: From: Ard Biesheuvel Date: Thu, 6 Dec 2018 08:29:03 +0100 Message-ID: Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages To: Andy Lutomirski Cc: Will Deacon , Rick Edgecombe , nadav.amit@gmail.com, Linux Kernel Mailing List , Daniel Borkmann , Jessica Yu , Steven Rostedt , Alexei Starovoitov , Linux-MM , Jann Horn , "Dock, Deneen T" , Peter Zijlstra , kristen@linux.intel.com, Andrew Morton , Ingo Molnar , anil.s.keshavamurthy@intel.com, Kernel Hardening , Masami Hiramatsu , naveen.n.rao@linux.vnet.ibm.com, "David S. Miller" , "" , Dave Hansen Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 6 Dec 2018 at 00:16, Andy Lutomirski wrote: > > On Wed, Dec 5, 2018 at 3:41 AM Will Deacon wrote: > > > > On Tue, Dec 04, 2018 at 12:09:49PM -0800, Andy Lutomirski wrote: > > > On Tue, Dec 4, 2018 at 12:02 PM Edgecombe, Rick P > > > wrote: > > > > > > > > On Tue, 2018-12-04 at 16:03 +0000, Will Deacon wrote: > > > > > 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 th= e underlying > > > > > > > pages, > > > > > > > it often leaves stale TLB entries to freed pages that could g= et re-used. > > > > > > > This is > > > > > > > undesirable for cases where the memory being freed has specia= l 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=E2=80=99t understand why we have t= he problem that this > > > > > > (your) patch-set deals with at all. We already change the mappi= ngs to make > > > > > > the memory wrAcked-by: Ard Biesheuvel itable before freeing the memory, so why can=E2=80=99t we make it > > > > > > non-executable at the same time? Actually, why do we make the m= odule memory, > > > > > > including its data executable before freeing it??? > > > > > > > > > > Yeah, this is really confusing, but I have a suspicion it's a com= bination > > > > > of the various different configurations and hysterical raisins. W= e can't > > > > > rely on module_alloc() allocating from the vmalloc area (see nios= 2) 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() altoget= her > > > > > afaict -- who cares about the memory attributes of a mapping that= 's about > > > > > to disappear anyway? > > > > > > > > > > Is it just nios2 that does something different? > > > > > > > > > Yea it is really intertwined. I think for x86, set_memory_nx everyw= here would > > > > solve it as well, in fact that was what I first thought the solutio= n should be > > > > until this was suggested. It's interesting that from the other thre= ad Masami > > > > Hiramatsu referenced, set_memory_nx was suggested last year and wou= ld have > > > > inadvertently blocked this on x86. But, on the other architectures = I have since > > > > learned it is a bit different. > > > > > > > > It looks like actually most arch's don't re-define set_memory_*, an= d so all of > > > > the frob_* functions are actually just noops. In which case allocat= ing RWX is > > > > needed to make it work at all, because that is what the allocation = is going to > > > > stay at. So in these archs, set_memory_nx won't solve it because it= will do > > > > nothing. > > > > > > > > On x86 I think you cannot get rid of disable_ro_nx fully because th= ere is the > > > > changing of the permissions on the directmap as well. You don't wan= t some other > > > > caller getting a page that was left RO when freed and then trying t= o write to > > > > it, if I understand this. > > > > > > > > > > Exactly. > > > > Of course, I forgot about the linear mapping. On arm64, we've just queu= ed > > support for reflecting changes to read-only permissions in the linear m= ap > > [1]. So, whilst the linear map is always non-executable, we will need t= o > > make parts of it writable again when freeing the module. > > > > > After slightly more thought, I suggest renaming VM_IMMEDIATE_UNMAP to > > > VM_MAY_ADJUST_PERMS or similar. It would have the semantics you want= , > > > but it would also call some arch hooks to put back the direct map > > > permissions before the flush. Does that seem reasonable? It would > > > need to be hooked up that implement set_memory_ro(), but that should > > > be quite easy. If nothing else, it could fall back to set_memory_ro(= ) > > > in the absence of a better implementation. > > > > You mean set_memory_rw() here, right? Although, eliding the TLB invalid= ation > > would open up a window where the vmap mapping is executable and the lin= ear > > mapping is writable, which is a bit rubbish. > > > > Right, and Rick pointed out the same issue. Instead, we should set > the direct map not-present or its ARM equivalent, then do the flush, > then make it RW. I assume this also works on arm and arm64, although > I don't know for sure. On x86, the CPU won't cache not-present PTEs. If we are going to unmap the linear alias, why not do it at vmalloc() time rather than vfree() time?