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=-2.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 ACEE1C64EB1 for ; Thu, 6 Dec 2018 20:26:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 657A120868 for ; Thu, 6 Dec 2018 20:26:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544127997; bh=ftZqrkDtY1yIjK9q0+a+7/Ca68Gk1u2vdzOlhWt+tVU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=mJ8577wONR9JSHEIGEEVf5pFSv9acS8MA3l7tFGnwI8N0MVQMwCVuvOQcB/eiepg4 G0Lqx65juaLpVdfQ5hgKRn8xaZA6/v3VqCc3x3JgavZv4W+Jpr0SsZQXOkG5j09wCK mL49nlqQip1VuWHW/XgsIN/IIYqZ2roN/RFtdq8E= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 657A120868 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1726180AbeLFU0g (ORCPT ); Thu, 6 Dec 2018 15:26:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:43706 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726154AbeLFU0e (ORCPT ); Thu, 6 Dec 2018 15:26:34 -0500 Received: from mail-wm1-f44.google.com (mail-wm1-f44.google.com [209.85.128.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6C46E2174D for ; Thu, 6 Dec 2018 20:26:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544127992; bh=ftZqrkDtY1yIjK9q0+a+7/Ca68Gk1u2vdzOlhWt+tVU=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=qdbb+FHPOhuZdHdyj8JEG0MeZDcHxK7wu/Fg4YxhKExI7gYrCOTes9CGACm/eyXvs dqWYP/99B6QhEvY5aDxeuXGg/0Lgh2ZOmnYtoIrLQczNq4tSyYgC61a1N+YvY43iD3 XBh9Xrs1vct5+62nuoAxKvdOznUTCfG/Fu5QF5io= Received: by mail-wm1-f44.google.com with SMTP id y139so2249289wmc.5 for ; Thu, 06 Dec 2018 12:26:32 -0800 (PST) X-Gm-Message-State: AA+aEWY3Nv0UZFLrM4Z0d/OiSC+odDoH7AuQCswCy1IC86IG3rUMCSHL 5pnDd1fwH3iOnZ1zoDoN7aS9FU8bIJ0GSAotsPuJLw== X-Google-Smtp-Source: AFSGD/UzVBzPdltDb5Gkw8KO8Lm4MVZ5KOQXcpvsRStxcUIti1RoNzIs1UKsNKl/BPevre/IdZZvkRI2vi+A9rwdEZ8= X-Received: by 2002:a1c:aa0f:: with SMTP id t15mr10023931wme.108.1544127990637; Thu, 06 Dec 2018 12:26:30 -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> <20181206190115.GC10086@cisco> In-Reply-To: From: Andy Lutomirski Date: Thu, 6 Dec 2018 12:26:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages To: Rick Edgecombe Cc: Andrew Lutomirski , Tycho Andersen , LKML , Daniel Borkmann , Ard Biesheuvel , Alexei Starovoitov , Steven Rostedt , Jessica Yu , Linux-MM , Jann Horn , Nadav Amit , "Dock, Deneen T" , Peter Zijlstra , Kristen Carlson Accardi , Andrew Morton , Will Deacon , Ingo Molnar , Anil S Keshavamurthy , Kernel Hardening , Masami Hiramatsu , "Naveen N . Rao" , "David S. Miller" , Network Development , 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, Dec 6, 2018 at 12:20 PM Edgecombe, Rick P wrote: > > On Thu, 2018-12-06 at 11:19 -0800, Andy Lutomirski wrote: > > On Thu, Dec 6, 2018 at 11:01 AM Tycho Andersen wrote: > > > > > > On Thu, Dec 06, 2018 at 10:53:50AM -0800, Andy Lutomirski wrote: > > > > > If we are going to unmap the linear alias, why not do it at vmall= oc() > > > > > time rather than vfree() time? > > > > > > > > That=E2=80=99s not totally nuts. Do we ever have code that expects = __va() to > > > > work on module data? Perhaps crypto code trying to encrypt static > > > > data because our APIs don=E2=80=99t understand virtual addresses. = I guess if > > > > highmem is ever used for modules, then we should be fine. > > > > > > > > RO instead of not present might be safer. But I do like the idea o= f > > > > renaming Rick's flag to something like VM_XPFO or VM_NO_DIRECT_MAP = and > > > > making it do all of this. > > > > > > Yeah, doing it for everything automatically seemed like it was/is > > > going to be a lot of work to debug all the corner cases where things > > > expect memory to be mapped but don't explicitly say it. And in > > > particular, the XPFO series only does it for user memory, whereas an > > > additional flag like this would work for extra paranoid allocations > > > of kernel memory too. > > > > > > > I just read the code, and I looks like vmalloc() is already using > > highmem (__GFP_HIGH) if available, so, on big x86_32 systems, for > > example, we already don't have modules in the direct map. > > > > So I say we go for it. This should be quite simple to implement -- > > the pageattr code already has almost all the needed logic on x86. The > > only arch support we should need is a pair of functions to remove a > > vmalloc address range from the address map (if it was present in the > > first place) and a function to put it back. On x86, this should only > > be a few lines of code. > > > > What do you all think? This should solve most of the problems we have. > > > > If we really wanted to optimize this, we'd make it so that > > module_alloc() allocates memory the normal way, then, later on, we > > call some function that, all at once, removes the memory from the > > direct map and applies the right permissions to the vmalloc alias (or > > just makes the vmalloc alias not-present so we can add permissions > > later without flushing), and flushes the TLB. And we arrange for > > vunmap to zap the vmalloc range, then put the memory back into the > > direct map, then free the pages back to the page allocator, with the > > flush in the appropriate place. > > > > I don't see why the page allocator needs to know about any of this. > > It's already okay with the permissions being changed out from under it > > on x86, and it seems fine. Rick, do you want to give some variant of > > this a try? > Hi, > > Sorry, I've been having email troubles today. > > I found some cases where vmap with PAGE_KERNEL_RO happens, which would no= t set > NP/RO in the directmap, so it would be sort of inconsistent whether the > directmap of vmalloc range allocations were readable or not. I couldn't s= ee any > places where it would cause problems today though. > > I was ready to assume that all TLBs don't cache NP, because I don't know = how > usages where a page fault is used to load something could work without lo= ts of > flushes. Or the architecture just fixes up the spurious faults, I suppose. I'm only well-educated on the x86 mmu. > If that's the case, then all archs with directmap permissions could > share a single vmalloc special permission flush implementation that works= like > Andy described originally. It could be controlled with an > ARCH_HAS_DIRECT_MAP_PERMS. We would just need something like set_pages_np= and > set_pages_rw on any archs with directmap permissions. So seems simpler to= me > (and what I have been doing) unless I'm missing the problem. Hmm. The only reason I've proposed anything fancier was because I was thinking of minimizing flushes, but I think I'm being silly. This sequence ought to work optimally: - vmalloc(..., VM_HAS_DIRECT_MAP_PERMS); /* no flushes */ - Write some data, via vmalloc's return address. - Use some set_memory_whatever() functions to update permissions, which will flush, hopefully just once. - Run the module code! - vunmap -- this will do a single flush that will fix everything. This does require that set_pages_np() or set_memory_np() or whatever exists and that it's safe to do that, then flush, and then set_pages_rw(). So maybe you want set_pages_np_noflush() and set_pages_rw_noflush() to make it totally clear what's supposed to happen. --Andy