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Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Borislav Petkov , Michael Roth , Vlastimil Babka , tony.luck@intel.com, npmccallum@redhat.com, brijesh.ksingh@gmail.com Subject: Re: [PATCH Part2 RFC v4 10/40] x86/fault: Add support to handle the RMP fault for user address To: Dave Hansen , x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org References: <20210707183616.5620-1-brijesh.singh@amd.com> <20210707183616.5620-11-brijesh.singh@amd.com> <3c6b6fc4-05b2-8d18-2eb8-1bd1a965c632@intel.com> <2b4accb6-b68e-02d3-6fed-975f90558099@amd.com> From: Brijesh Singh Message-ID: <5592d8ff-e2c3-6474-4a10-96abe1962d6f@amd.com> Date: Mon, 12 Jul 2021 11:11:54 -0500 User-Agent: Mozilla/5.0 (X11; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?dUdjekZiMXVQSDE1akJYUXFFVEJCUzQ0cjVvQ3dpaUNhWTVQeGVHWFI5OExw?= =?utf-8?B?UkYra0JYYkJyM0JVdUt6RGxxdmluait3bCtJODFnblBGcFJpcDd3RklUWThL?= =?utf-8?B?VHhEbWJWd3VZYUdWWW1VM1lPTU9uWWdzajloS2FGRjFCeTBreUtJRms5cEpZ?= =?utf-8?B?ZmRWejZ1OEE0eHJjaVlITWJjYmF0Mk9DdGNHNjMwdFlkNC9zbzBHM2R3cUh3?= =?utf-8?B?c3luUXg5QUVnVnlUTVgrWisycy8wdDNtWXZuWjh4RzNwY0ZvekxMT2NBcm14?= =?utf-8?B?MmExT1ZlWGZLOEUwdUM3dzFRbVNKT09JVThtMGsxOHozZ3VYaFo2MDBqVXdw?= =?utf-8?B?UzkwV2RNT2JYMUMyc2Z1TGh3Q3MyN3Z3MDZwU0V2WmFYdHpmc0ZSMEV2SWF2?= =?utf-8?B?NHhDMDVxcDJuK2pPb0g5K3J4TWlCY3k5RHdsNnVLV3pOQnl3Y2ZPWGtPaWRE?= =?utf-8?B?bm9Oem83YmJlRUVHbnZsZzY5QTFLazYzK0tQeUpVTjdXNytzR0k4aU5EcVMr?= =?utf-8?B?YTF2SzFsbGFpeUFkU0lPa0lTZFBBa2owK2MyWUtLdHNBT3dJM1FNMm9MbmNV?= =?utf-8?B?RTNvT2l2cHBqR0dSUG9oelpCQ2VLVmdBM0xIcGd0blpRTE96QXJKSzFwSXln?= =?utf-8?B?R2svT0hWN1lEYkd4R25SYmI5ejl0UHVvQ2Y2b3FLejBXNnByLzJUWjhROVN6?= =?utf-8?B?eTQ3bVlRUDl0Njl5L0liVU5kVGhSdzAxeVZoVGVpMFhYRUpTVXhGOXhzNWQy?= =?utf-8?B?YXdnY0Q5S21HNk9GYVBHVlNHR2MyTEovRUJjVVdSeWRtS3B3S003cFdrNTNJ?= =?utf-8?B?ZWgyOFBiQ2pmSS9mUWoyRVlvNklZTjNwY1VOVVFSZm9pZkVqc05vT0dOb3lu?= =?utf-8?B?SVdaSzRKaEllWU1pM29BN0NjeUZZR01RRitWUnhVNXJrbHRURG14MnZVOEtM?= =?utf-8?B?bElvOTBuajIxTW5rSURuay9aNEdGUFQvckJ5RDUvc281a0l4VkZBSHBud0tu?= =?utf-8?B?VVF1MWdMdVZMcmU5c0Eweno0ai9YbjY0ZGJFaGJLVFdhc3oxN2ZrbGN6UC9M?= =?utf-8?B?K3FRcjlaUUJjWERnOFdTQTUxY01nRVJXK3dYTmpmaFlGR0tvVU5JLzhKNVow?= =?utf-8?B?b01JUWFGMUVoZ0Y3TUc5cmJ0TmptMWNhR242VVhDUFBla2h4MEZUR3FjdnFl?= =?utf-8?B?QzREQkNTTUo0M1FmdE9pWmJ5OXRlcnNDWkVYYWZ0YzdKZFpvVno1bVF4WGs4?= =?utf-8?B?Mk45THVZUHo0eHlaWUJ1eWJjTCttSHowTFlNdGcwWElLbmVsV2NCWnFaTzdR?= =?utf-8?B?NFdpSW9ieFRqV1EybEZEbXpLUzYvQ2FPcFZidDNIbGxCM3A2cmI5a2NuV0Jv?= =?utf-8?B?RVBxYzc1TzJrbTVjbHBZU3NWLzJrYWJGb1BmaCtDNER5aWw1T3BpNENtd3Vi?= =?utf-8?B?a3RRYjlHOXNxR05aUjN3bnRyVTZGbWRYZmtvdFdWTG5FMG5BNloxOHNKQnR6?= =?utf-8?B?Wi8yMkhVMFJwWW5Fc3ZaSkRoNFZkTjFLVExDbStmK1h1N0tGNlBlQ1B6V3hS?= =?utf-8?B?YjBjSDlmWGFJaVlsT3BPNWdZemhpLytoR3o5c21ibG9OcFdCYkZNZU10d0dO?= =?utf-8?B?eWg3SEdpK1VPZkZ4RENFbzZxS0NoQW5TL3ZhQ1hiVkJmM01vc2J6UG4xdFp4?= =?utf-8?B?aVZqR3o1SmRyWWRtajMwVHdEdGt6bWpneVdmeUxJbFppcmpaTGp3bnQzRkFC?= =?utf-8?Q?SeZ1TwOTTM2KLgO8QngkHopSAQOnTIR5/x1ocYh?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: e41cf51f-3c88-49e3-985a-08d9454fc538 X-MS-Exchange-CrossTenant-AuthSource: SN6PR12MB2718.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jul 2021 16:11:56.5418 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: pmBQGVfdthSPCUJKuApvkfYFauUfNjy6SVjAfhVppFjZYsgrAgP6uwb+8ldXBWfWER+yrxNfNv8apnQIClOG4g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR12MB2832 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/12/21 11:00 AM, Dave Hansen wrote: > On 7/12/21 8:43 AM, Brijesh Singh wrote: >>>> +    /* >>>> +     * The backing page level is higher than the RMP page level, >>>> request >>>> +     * to split the page. >>>> +     */ >>>> +    if (level > rmp_level) >>>> +        return RMP_FAULT_PAGE_SPLIT; >>> >>> This can theoretically trigger on a hugetlbfs page.  Right? >> >> Yes, theoretically. >> >> In the current implementation, the VMM is enlightened to not use the >> hugetlbfs for backing page when creating the SEV-SNP guests. > > "The VMM"? I was meaning a userspace qemu. > > We try to write kernel code so that it "works" and doesn't do unexpected > things with whatever userspace might throw at it. This seems to be > written with an assumption that no VMM will ever use hugetlbfs with SEV-SNP. > > That worries me. Not only because someone is sure to try it, but it's > the kind of assumption that an attacker or a fuzzer might try. > > Could you please test this kernel code in practice with hugetblfs? Yes, I will make sure that hugetlbfs path is tested in non-RFC version. > >>> I also suspect you can just set VM_FAULT_SIGBUS and let the do_sigbus() >>> call later on in the function do its work. >>>>   +static int handle_split_page_fault(struct vm_fault *vmf) >>>> +{ >>>> +    if (!IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) >>>> +        return VM_FAULT_SIGBUS; >>>> + >>>> +    __split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL); >>>> +    return 0; >>>> +} >>> >>> What will this do when you hand it a hugetlbfs page? >> >> VMM is updated to not use the hugetlbfs when creating SEV-SNP guests. >> So, we should not run into it. > > Please fix this code to handle hugetlbfs along with any other non-THP > source of level>0 mappings. DAX comes to mind. "Handle" can mean > rejecting these. You don't have to find some way to split them and make > the VM work, just fail safely, ideally as early as possible. > > To me, this is a fundamental requirement before this code can be accepted. Understood, if userspace decided to use the hugetlbfs backing pages then I believe earliest we can detect is when we go about adding the pages in the RMP table. I'll add a check, and fail the page state change. -Brijesh