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Thu, 29 Dec 2022 16:25:17 +0000 Received: from BYAPR21MB1688.namprd21.prod.outlook.com ([fe80::db1a:4e71:c688:b7b1]) by BYAPR21MB1688.namprd21.prod.outlook.com ([fe80::db1a:4e71:c688:b7b1%7]) with mapi id 15.20.5986.007; Thu, 29 Dec 2022 16:25:16 +0000 From: "Michael Kelley (LINUX)" To: Borislav Petkov CC: "hpa@zytor.com" , KY Srinivasan , Haiyang Zhang , "wei.liu@kernel.org" , Dexuan Cui , "luto@kernel.org" , "peterz@infradead.org" , "davem@davemloft.net" , "edumazet@google.com" , "kuba@kernel.org" , "pabeni@redhat.com" , "lpieralisi@kernel.org" , "robh@kernel.org" , "kw@linux.com" , "bhelgaas@google.com" , "arnd@arndb.de" , "hch@infradead.org" , "m.szyprowski@samsung.com" , "robin.murphy@arm.com" , "thomas.lendacky@amd.com" , "brijesh.singh@amd.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "dave.hansen@linux.intel.com" , Tianyu Lan , "kirill.shutemov@linux.intel.com" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "ak@linux.intel.com" , "isaku.yamahata@intel.com" , "Williams, Dan J" , "jane.chu@oracle.com" , "seanjc@google.com" , "tony.luck@intel.com" , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-arch@vger.kernel.org" , "iommu@lists.linux.dev" Subject: RE: [Patch v4 04/13] x86/mm: Handle decryption/re-encryption of bss_decrypted consistently Thread-Topic: [Patch v4 04/13] x86/mm: Handle decryption/re-encryption of bss_decrypted consistently Thread-Index: AQHZBf6qXxv12SnI/0WwIL+HXSylNa6E8yMAgAA/XSA= Date: Thu, 29 Dec 2022 16:25:16 +0000 Message-ID: References: <1669951831-4180-1-git-send-email-mikelley@microsoft.com> <1669951831-4180-5-git-send-email-mikelley@microsoft.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=05d70819-cd30-4435-acaa-8b6d27fe6b05;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2022-12-29T16:04:35Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR21MB1688.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 08c797d6-59b8-4123-4791-08dae9b9450e X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Dec 2022 16:25:16.2975 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: ERmIITzF1+DsbHy66+laiCVWrUnjR/Uy8ESccwh+bT7cNA8HvFb0jO/ZP9927b/K5sh5apphKmZ61my3rzhBhOzrIbsFHwDJQxLYf6fxhNY= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR21MB3355 X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO, RCVD_IN_DNSWL_NONE,SPF_HELO_PASS,SPF_NONE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Borislav Petkov Sent: Thursday, December 29, 2022 4:18= AM >=20 > On Thu, Dec 01, 2022 at 07:30:22PM -0800, Michael Kelley wrote: > > Current code in sme_postprocess_startup() decrypts the bss_decrypted > > section when sme_me_mask is non-zero. But code in > > mem_encrypt_free_decrypted_mem() re-encrypts the unused portion based > > on CC_ATTR_MEM_ENCRYPT. In a Hyper-V guest VM using vTOM, these > > conditions are not equivalent as sme_me_mask is always zero when > > using vTOM. Consequently, mem_encrypt_free_decrypted_mem() attempts > > to re-encrypt memory that was never decrypted. > > > > Fix this in mem_encrypt_free_decrypted_mem() by conditioning the > > re-encryption on the same test for non-zero sme_me_mask. Hyper-V > > guests using vTOM don't need the bss_decrypted section to be > > decrypted, so skipping the decryption/re-encryption doesn't cause > > a problem. >=20 > Lemme simplify the formulations a bit: >=20 > "sme_postprocess_startup() decrypts the bss_decrypted ection when me_mask > sme_is non-zero. >=20 > mem_encrypt_free_decrypted_mem() re-encrypts the unused portion based on > CC_ATTR_MEM_ENCRYPT. >=20 > In a Hyper-V guest VM using vTOM, these conditions are not equivalent > as sme_me_mask is always zero when using vTOM. Consequently, > mem_encrypt_free_decrypted_mem() attempts to re-encrypt memory that was > never decrypted. >=20 > So check sme_me_mask in mem_encrypt_free_decrypted_mem() too. >=20 > Hyper-V guests using vTOM don't need the bss_decrypted section to be > decrypted, so skipping the decryption/re-encryption doesn't cause a > problem." Work for me. I'll pick up the new wording in v5. >=20 > > Fixes: e9d1d2bb75b2 ("treewide: Replace the use of mem_encrypt_active()= with > cc_platform_has()") >=20 > So when you say Fixes - this is an issue only for vTOM-using VMs and > before yours, there were none. And yours needs more enablement than just > this patch. >=20 > So does this one really need to be backported to stable@? >=20 > I'm asking because there's AI which will pick it up based on this Fixes > tag up but that AI is still not that smart to replace us all. :-) >=20 I'm ambivalent on the backport to stable. One might argue that older kernel versions are conceptually wrong in using different conditions for the decryption and re-encryption. But as you said, they aren't broken from a practical standpoint because sme_me_mask and CC_ATTR_MEM_ENCRYPT are equivalent prior to my patch set. However, the email thread with Sathyanarayanan Kuppuswamy, Tom Lendacky, and Dexuan Cui concluded that a Fixes: tag is appropriate. See https://lore.kernel.org/lkml/fbf2cdcc-4ff7-b466-a6af-7a147f3bc94d@amd.com/ and https://lore.kernel.org/lkml/BYAPR21MB1688A31ED795ED1B5ACB6D26D7099@BYAPR21= MB1688.namprd21.prod.outlook.com/ Michael