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=-5.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,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 D0EB3C33CAC for ; Thu, 6 Feb 2020 17:37:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B1D4621927 for ; Thu, 6 Feb 2020 17:37:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727840AbgBFRhA (ORCPT ); Thu, 6 Feb 2020 12:37:00 -0500 Received: from mga02.intel.com ([134.134.136.20]:10353 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726990AbgBFRhA (ORCPT ); Thu, 6 Feb 2020 12:37:00 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Feb 2020 09:37:00 -0800 X-IronPort-AV: E=Sophos;i="5.70,410,1574150400"; d="scan'208";a="220510906" Received: from kcaccard-mobl.amr.corp.intel.com (HELO kcaccard-mobl1.jf.intel.com) ([10.24.10.96]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 06 Feb 2020 09:37:00 -0800 Message-ID: Subject: Re: [RFC PATCH 08/11] x86: Add support for finer grained KASLR From: Kristen Carlson Accardi To: Kees Cook , Andy Lutomirski Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Arjan van de Ven , Rick Edgecombe , X86 ML , LKML , Kernel Hardening Date: Thu, 06 Feb 2020 09:36:59 -0800 In-Reply-To: <202002060353.A6A064A@keescook> References: <20200205223950.1212394-1-kristen@linux.intel.com> <20200205223950.1212394-9-kristen@linux.intel.com> <202002060353.A6A064A@keescook> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2020-02-06 at 03:56 -0800, Kees Cook wrote: > On Wed, Feb 05, 2020 at 05:17:11PM -0800, Andy Lutomirski wrote: > > On Wed, Feb 5, 2020 at 2:39 PM Kristen Carlson Accardi > > wrote: > > > At boot time, find all the function sections that have separate > > > .text > > > sections, shuffle them, and then copy them to new locations. > > > Adjust > > > any relocations accordingly. > > > > > > + sort(base, num_syms, sizeof(int), kallsyms_cmp, > > > kallsyms_swp); > > > > Hah, here's a huge bottleneck. Unless you are severely > > memory-constrained, never do a sort with an expensive swap function > > like this. Instead allocate an array of indices that starts out as > > [0, 1, 2, ...]. Sort *that* where the swap function just swaps the > > indices. Then use the sorted list of indices to permute the actual > > data. The result is exactly one expensive swap per item instead of > > one expensive swap per swap. > > I think there are few places where memory-vs-speed need to be > examined. > I remain surprised about how much memory the entire series already > uses > (58MB in my local tests), but I suspect this is likely dominated by > the > two factors: a full copy of the decompressed kernel, and that the > "allocator" in the image doesn't really implement free(): > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/decompress/mm.h#n55 > Yes - that was a huge issue (that free() doesn't actually...). Having to do the copy really caused me to need to bump up the boot heap. Thankfully, this is a readily solvable problem. I think there's a temptation to focus too hard on the boot latency. While I measured this on a reasonably fast system, we aren't talking minutes of latency here, just a second or a second and a half. I know there are those who sweat the milliseconds on booting vms, but I expect they might just turn this feature off anyway. That said, there are absolutely a lot of great ideas for improving things here that I am excited to try should people be interested enough in this feature for me to take it to the next stage.