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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 65001C433EF for ; Mon, 18 Jun 2018 13:12:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F8662086A for ; Mon, 18 Jun 2018 13:12:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F8662086A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com 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 S933947AbeFRNMv (ORCPT ); Mon, 18 Jun 2018 09:12:51 -0400 Received: from mga06.intel.com ([134.134.136.31]:11429 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932843AbeFRNMu (ORCPT ); Mon, 18 Jun 2018 09:12:50 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jun 2018 06:12:49 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,239,1526367600"; d="scan'208";a="50220327" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga008.jf.intel.com with ESMTP; 18 Jun 2018 06:12:46 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id C9B68FA; Mon, 18 Jun 2018 16:12:47 +0300 (EEST) Date: Mon, 18 Jun 2018 16:12:47 +0300 From: "Kirill A. Shutemov" To: Dave Hansen Cc: Ingo Molnar , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Tom Lendacky , Kai Huang , Jacob Pan , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv3 14/17] x86/mm: Introduce direct_mapping_size Message-ID: <20180618131247.myt6vjiav3nwww5p@black.fi.intel.com> References: <20180612143915.68065-1-kirill.shutemov@linux.intel.com> <20180612143915.68065-15-kirill.shutemov@linux.intel.com> <4ece14a4-27bd-e10a-4c2c-822c3e629dcd@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4ece14a4-27bd-e10a-4c2c-822c3e629dcd@intel.com> User-Agent: NeoMutt/20170714-126-deb55f (1.8.3) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 13, 2018 at 06:37:07PM +0000, Dave Hansen wrote: > On 06/12/2018 07:39 AM, Kirill A. Shutemov wrote: > > Kernel need to have a way to access encrypted memory. We are going to > "The kernel needs"... > > > use per-KeyID direct mapping to facilitate the access with minimal > > overhead. > > What are the security implications of this approach? I'll add this to the message: Per-KeyID mappings require a lot more virtual address space. On 4-level machine with 64 KeyIDs we max out 46-bit virtual address space dedicated for direct mapping with 1TiB of RAM. Given that we round up any calculation on direct mapping size to 1TiB, we effectively claim all 46-bit address space for direct mapping on such machine regardless of RAM size. Increased usage of virtual address space has implications for KASLR: we have less space for randomization. With 64 TiB claimed for direct mapping with 4-level we left with 27 TiB of entropy to place page_offset_base, vmalloc_base and vmemmap_base. 5-level paging provides much wider virtual address space and KASLR doesn't suffer significantly from per-KeyID direct mappings. It's preferred to run MKTME with 5-level paging. > > Direct mapping for each KeyID will be put next to each other in the > > That needs to be "a direct mapping" or "the direct mapping". It's > missing an article to start the sentence. Okay. > > virtual address space. We need to have a way to find boundaries of > > direct mapping for particular KeyID. > > > > The new variable direct_mapping_size specifies the size of direct > > mapping. With the value, it's trivial to find direct mapping for > > KeyID-N: PAGE_OFFSET + N * direct_mapping_size. > > I think this deserves an update to Documentation/x86/x86_64/mm.txt, no? Right, I'll update it. > > Size of direct mapping is calculated during KASLR setup. If KALSR is > > disable it happens during MKTME initialization. > > "disabled" > > > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c > > index 4408cd9a3bef..3d8ef8cb97e1 100644 > > --- a/arch/x86/mm/kaslr.c > > +++ b/arch/x86/mm/kaslr.c > > @@ -69,6 +69,15 @@ static inline bool kaslr_memory_enabled(void) > > return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN); > > } > > > > +#ifndef CONFIG_X86_INTEL_MKTME > > +static void __init setup_direct_mapping_size(void) > > +{ > > + direct_mapping_size = max_pfn << PAGE_SHIFT; > > + direct_mapping_size = round_up(direct_mapping_size, 1UL << TB_SHIFT); > > + direct_mapping_size += (1UL << TB_SHIFT) * CONFIG_MEMORY_PHYSICAL_PADDING; > > +} > > +#endif > > Comments, please. Okay. > > /* Initialize base and padding for each memory region randomized with KASLR */ > > void __init kernel_randomize_memory(void) > > { > > @@ -93,7 +102,11 @@ void __init kernel_randomize_memory(void) > > if (!kaslr_memory_enabled()) > > return; > > > > - kaslr_regions[0].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT); > > + /* > > + * Upper limit for direct mapping size is 1/4 of whole virtual > > + * address space > > + */ > > + kaslr_regions[0].size_tb = 1 << (__VIRTUAL_MASK_SHIFT - 1 - TB_SHIFT); > > Is this a cleanup that can be separate? Right. I'll split it up. > > kaslr_regions[1].size_tb = VMALLOC_SIZE_TB; > > > > /* > > @@ -101,8 +114,10 @@ void __init kernel_randomize_memory(void) > > * add padding if needed (especially for memory hotplug support). > > */ > > BUG_ON(kaslr_regions[0].base != &page_offset_base); > > - memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) + > > - CONFIG_MEMORY_PHYSICAL_PADDING; > > + > > + setup_direct_mapping_size(); > > + > > + memory_tb = direct_mapping_size * mktme_nr_keyids + 1; > > What's the +1 for? Is "mktme_nr_keyids" 0 for "MKTME unsupported"? > That needs to be called out, I think. I'll add a comment. > > /* Adapt phyiscal memory region size based on available memory */ > > if (memory_tb < kaslr_regions[0].size_tb) > > diff --git a/arch/x86/mm/mktme.c b/arch/x86/mm/mktme.c > > index 43a44f0f2a2d..3e5322bf035e 100644 > > --- a/arch/x86/mm/mktme.c > > +++ b/arch/x86/mm/mktme.c > > @@ -89,3 +89,51 @@ static bool need_page_mktme(void) > > struct page_ext_operations page_mktme_ops = { > > .need = need_page_mktme, > > }; > > + > > +void __init setup_direct_mapping_size(void) > > +{ > > + unsigned long available_va; > > + > > + /* 1/4 of virtual address space is didicated for direct mapping */ > > + available_va = 1UL << (__VIRTUAL_MASK_SHIFT - 1); > > + > > + /* How much memory the systrem has? */ > > + direct_mapping_size = max_pfn << PAGE_SHIFT; > > + direct_mapping_size = round_up(direct_mapping_size, 1UL << 40); > > + > > + if (mktme_status != MKTME_ENUMERATED) > > + goto out; > > + > > + /* > > + * Not enough virtual address space to address all physical memory with > > + * MKTME enabled. Even without padding. > > + * > > + * Disable MKTME instead. > > + */ > > + if (direct_mapping_size > available_va / mktme_nr_keyids + 1) { > > + pr_err("x86/mktme: Disabled. Not enough virtual address space\n"); > > + pr_err("x86/mktme: Consider switching to 5-level paging\n"); > > + mktme_disable(); > > + goto out; > > + } > > + > > + /* > > + * Virtual address space is divided between per-KeyID direct mappings. > > + */ > > + available_va /= mktme_nr_keyids + 1; > > +out: > > + /* Add padding, if there's enough virtual address space */ > > + direct_mapping_size += (1UL << 40) * CONFIG_MEMORY_PHYSICAL_PADDING; > > + if (direct_mapping_size > available_va) > > + direct_mapping_size = available_va; > > +} > > Do you really need two copies of this function? Shouldn't it see > mktme_status!=MKTME_ENUMERATED and just jump out? How is the code > before that "goto out" different from the CONFIG_MKTME=n case? mktme.c is not compiled for CONFIG_MKTME=n. -- Kirill A. Shutemov