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From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Kai Huang <kai.huang@linux.intel.com>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv4 15/18] x86/mm: Calculate direct mapping size
Date: Mon, 9 Jul 2018 14:32:50 -0400	[thread overview]
Message-ID: <20180709183250.GJ6873@char.US.ORACLE.com> (raw)
In-Reply-To: <20180626142245.82850-16-kirill.shutemov@linux.intel.com>

On Tue, Jun 26, 2018 at 05:22:42PM +0300, Kirill A. Shutemov wrote:
> The kernel needs to have a way to access encrypted memory. We have two
> option on how approach it:
> 
>  - Create temporary mappings every time kernel needs access to encrypted
>    memory. That's basically brings highmem and its overhead back.
> 
>  - Create multiple direct mappings, one per-KeyID. In this setup we
>    don't need to create temporary mappings on the fly -- encrypted
>    memory is permanently available in kernel address space.
> 
> We take the second approach as it has lower overhead.
> 
> It's worth noting that with per-KeyID direct mappings compromised kernel
> would give access to decrypted data right away without additional tricks
> to get memory mapped with the correct KeyID.
> 
> 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.


Why not make this a config dependency then?

  reply	other threads:[~2018-07-09 18:33 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-26 14:22 [PATCHv4 00/18] MKTME enabling Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 01/18] mm: Do no merge VMAs with different encryption KeyIDs Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 02/18] mm/ksm: Do not merge pages with different KeyIDs Kirill A. Shutemov
2018-07-09 18:03   ` Konrad Rzeszutek Wilk
2018-06-26 14:22 ` [PATCHv4 03/18] mm/page_alloc: Unify alloc_hugepage_vma() Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 04/18] mm/page_alloc: Handle allocation for encrypted memory Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 05/18] mm/khugepaged: Handle encrypted pages Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 06/18] x86/mm: Mask out KeyID bits from page table entry pfn Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 07/18] x86/mm: Introduce variables to store number, shift and mask of KeyIDs Kirill A. Shutemov
2018-07-09 18:09   ` Konrad Rzeszutek Wilk
2018-07-10 10:48     ` Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 08/18] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify() Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 09/18] x86/mm: Implement page_keyid() using page_ext Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 10/18] x86/mm: Implement vma_keyid() Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 11/18] x86/mm: Implement prep_encrypted_page() and arch_free_page() Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 12/18] x86/mm: Rename CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 13/18] x86/mm: Allow to disable MKTME after enumeration Kirill A. Shutemov
2018-07-09 18:20   ` Konrad Rzeszutek Wilk
2018-07-10 10:49     ` Kirill A. Shutemov
2018-07-10 11:21       ` Konrad Rzeszutek Wilk
2018-06-26 14:22 ` [PATCHv4 14/18] x86/mm: Detect MKTME early Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 15/18] x86/mm: Calculate direct mapping size Kirill A. Shutemov
2018-07-09 18:32   ` Konrad Rzeszutek Wilk [this message]
2018-06-26 14:22 ` [PATCHv4 16/18] x86/mm: Implement sync_direct_mapping() Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 17/18] x86/mm: Handle encrypted memory in page_to_virt() and __pa() Kirill A. Shutemov
2018-06-26 16:38   ` Dave Hansen
2018-06-27 21:56     ` Kirill A. Shutemov
2018-06-26 14:22 ` [PATCHv4 18/18] x86: Introduce CONFIG_X86_INTEL_MKTME Kirill A. Shutemov
2018-06-26 17:30   ` Randy Dunlap
2018-06-27 21:57     ` Kirill A. Shutemov
2018-06-27 23:48       ` Randy Dunlap
2018-07-09 18:36   ` Konrad Rzeszutek Wilk
2018-07-09 18:44     ` Dave Hansen
2018-07-09 18:52       ` Konrad Rzeszutek Wilk
2018-07-09 18:59         ` Dave Hansen
2018-07-09 20:29           ` Konrad Rzeszutek Wilk

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