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Shutemov" , Andi Kleen , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com Subject: Re: [PATCH Part1 v5 32/38] x86/sev: enable SEV-SNP-validated CPUID in #VC handlers Message-ID: <20210827183240.f7zvo3ujkeohmlrt@amd.com> References: <20210820151933.22401-1-brijesh.singh@amd.com> <20210820151933.22401-33-brijesh.singh@amd.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SA0PR11CA0103.namprd11.prod.outlook.com (2603:10b6:806:d1::18) To CH2PR12MB4133.namprd12.prod.outlook.com (2603:10b6:610:7a::13) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from localhost (165.204.77.11) by SA0PR11CA0103.namprd11.prod.outlook.com (2603:10b6:806:d1::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4457.17 via Frontend Transport; Mon, 30 Aug 2021 15:55:51 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 039f3be5-db48-4c08-4705-08d96bcea45c X-MS-TrafficTypeDiagnostic: CH2PR12MB4039: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?xDU8haMAsAxwWuzXEOze5aaEYXWKgnJo8xZfDfVyg459xAHfipvRiX48U9pK?= =?us-ascii?Q?L4dlu4O/BhqVLTXA0Dm2Q8KVVJfb059omGye8OxxPD9bqXRhM5jZrWLHl/p8?= =?us-ascii?Q?tSwWkjUyUWoU5sTaqkEt8fpVvQnmW7JzCRoewRqq5xvGV+1MFjigKvxzN0t5?= =?us-ascii?Q?kxSNYf3STMsYf3bNzd14+vhN/ecleMhGEAoYbYVDxLatWgDla4oIe+kXQsPO?= =?us-ascii?Q?t/vwTVkhm0eCs3UY2eyBW5ZobWDm35KOQRRD0+xus5EpH3GmVSFIQnNYG8+m?= =?us-ascii?Q?GrolxJwUHxh0kCSPdrNxWhahvsUo82T1OWFHWQBvt8Zc+wTDjzj4y+Anmxzp?= =?us-ascii?Q?0WxaR+MYp+IlQEaUh2UGd1jdKK+rQI4ZVyl8FdD8G8y8UAHPkAqmu6S2lPTE?= =?us-ascii?Q?VsajGKZRVQlUym9s/50dj8ekdeG+iwBxY5BzKA8d1jyBwd8oyfodzwRPH3qG?= =?us-ascii?Q?vtB/de5SYjaRHHqAN8m9ExtL+CgZbWebH9erKV3c48zCAWeF+Mr5mEBJhhUZ?= =?us-ascii?Q?kMd4qFxFlknewcE4bpw4vIYNrz198wMx2gkyVvI7mjPbYFFbIeizQd+oDpzl?= =?us-ascii?Q?f53KM+2oofQOfFAt+Oq1LuSWLa5AZ/9qBdMDKkBpP302gVGpL5Qjq8B1Newa?= =?us-ascii?Q?f0XaWLz89A/TLoxq4EGgskDvaxHhUy7pSV2W4ON/DsasNrmZKaeqSG+E3AvH?= =?us-ascii?Q?maFYrKxQ+T5GUKZ6EclSTPEwQi5BCiYhfCl83KMTQKgVPf4NbOLp5Tmc3Avn?= =?us-ascii?Q?74efkNlEae546z3oh3xXUh7VsR1UtaHgENrDy3GRPh3DYi3lkdOeX0SeWL5R?= =?us-ascii?Q?D48wvkOsZfFkQe8apd+bLtn2flk5J7rNz+GYKJG0q3VtbbcrAgcZ8y9WsYzq?= =?us-ascii?Q?zFyASl3gbVftL1r2pfx5Vkt6mM7SDGlET0Nb7WRZMqbg99A16po6ICW/Sj3R?= =?us-ascii?Q?fb41fUokb10d2CZ6l0Si/FbqMoK2wrjR2nCNogY+FVUVjgCwLyjOSNPKe8oX?= =?us-ascii?Q?ezq1rbxCgw3JizR5QjH/g4txDW29DsmThTjTUQiARgr0yPwIB8pA8r+d/dMR?= =?us-ascii?Q?EFNk2YHyBa7oPfc4p2uAkcdGZBNXfSYf6kv/lyhj1cLg+EowNXX5zjFMj82v?= =?us-ascii?Q?oyGd15Smbp5sKuBYo2j4ynC1zACiz1eYBrf02qzsixGUUzFRcueKRXP4ajSO?= =?us-ascii?Q?oeCEd38ISmNTB05Dkn9Wh1eqRV64EItBQBPULQMtQ73sMZe4qIWo8jiJgwv8?= =?us-ascii?Q?UJfGzf2ucbxUuxp5j6FMPKPzZ4QT3WIHOJrFYDr4sNxpyphbPjvyIm70auZv?= =?us-ascii?Q?mGrtNExXOxox5i7LhFmcyP/C?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 039f3be5-db48-4c08-4705-08d96bcea45c X-MS-Exchange-CrossTenant-AuthSource: CH2PR12MB4133.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Aug 2021 15:55:51.8086 (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: JO0+/kekY17av6x0Mx6pMDg0/FYoYZAn3NgzxDN8vB3mYAd/DCRcXBXiAayuB3IEe+kYYuVS1qxvCji2i0Wnmw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4039 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 27, 2021 at 05:18:49PM +0200, Borislav Petkov wrote: > On Fri, Aug 20, 2021 at 10:19:27AM -0500, Brijesh Singh wrote: > > From: Michael Roth > > > > This adds support for utilizing the SEV-SNP-validated CPUID table in > > s/This adds support for utilizing/Utilize/ > > Yap, it can really be that simple. :) > > > the various #VC handler routines used throughout boot/run-time. Mostly > > this is handled by re-using the CPUID lookup code introduced earlier > > for the boot/compressed kernel, but at various stages of boot some work > > needs to be done to ensure the CPUID table is set up and remains > > accessible throughout. The following init routines are introduced to > > handle this: > > Do not talk about what your patch does - that should hopefully be > visible in the diff itself. Rather, talk about *why* you're doing what > you're doing. I'll get this cleaned up. > > > sev_snp_cpuid_init(): > > This one is not really introduced - it is already there. > > > > So this patch is making my head spin. It seems we're dancing a lot of > dance just to have our CPUID page present at all times. Which begs the > question: do we need it during the whole lifetime of the guest? > > Regardless, I think this can be simplified by orders of > magnitude if we allocated statically 4K for that CPUID page in > arch/x86/boot/compressed/mem_encrypt.S, copied the supplied CPUID page > from the firmware to it and from now on, work with our own copy. That makes sense. I was thinking it was safer to work with the FW page since it would be less susceptible to something like a buffer overflow modifying the CPUID table, but __ro_after_init seems like it would provide similar protections. And yes, would definitely be great to avoid the need for so many [re-]init routines. > > You probably would need to still remap it for kernel proper but it would > get rid of all that crazy in this patch here. > > Hmmm? If the memory is allocated in boot/compressed/mem_encrypt.S, wouldn't kernel proper still need to create a static buffer for its copy? And if not, wouldn't boot compressed still need a way to pass the PA of this buffer? That seems like it would need to be done via boot_params. It seems like it would also need to be marked as reserved as well since kernel proper could no longer rely on the EFI map to handle it. I've been testing a similar approach based on your suggestion that seems to work out pretty well, but there's still some ugliness due to the fixup_pointer() stuff that's needed early during snp_cpuid_init() in kernel proper, which results in the need for 2 init routines there. Not sure if there's a better way to handle it, but it's a lot better than 4 init routines at least, and with this there is no longer any need to store the address/size of the FW page: in arch/x86/kernel/sev-shared.c: /* Firmware-enforced limit on CPUID table entries */ #define SNP_CPUID_COUNT_MAX 64 struct sev_snp_cpuid_info { u32 count; u32 __reserved1; u64 __reserved2; struct sev_snp_cpuid_fn fn[SNP_CPUID_COUNT_MAX]; } __packed; static struct snp_cpuid_info cpuid_info_copy __ro_after_init; static const struct snp_cpuid_info *cpuid_info __ro_after_init; static int sev_snp_cpuid_enabled __ro_after_init; /* * Initial set up of CPUID table when running identity-mapped. */ #ifdef __BOOT_COMPRESSED void sev_snp_cpuid_init(struct boot_params *bp) #else void __init sev_snp_cpuid_init(struct boot_params *bp, unsigned long physaddr) #endif { const struct sev_snp_cpuid_info *cpuid_info_fw; cpuid_info_fw = snp_probe_cpuid_info(bp); if (!cpuid_info_fw) return; #ifdef __BOOT_COMPRESSED cpuid_info2 = &cpuid_info_copy; #else /* Kernel proper calls this while pointer fixups are still needed. */ cpuid_info2 = (const struct sev_snp_cpuid_info *) ((void *)&cpuid_info_copy - (void *)_text + physaddr); #endif memcpy((struct sev_snp_cpuid_info *)cpuid_info2, cpuid_info_fw, sizeof(*cpuid_info2)); sev_snp_cpuid_enabled = 1; } #ifndef __BOOT_COMPRESSED /* * This is called after the switch to virtual kernel addresses. At this * point pointer fixups are no longer needed, and the virtual address of * the CPUID info buffer has changed, so re-initialize the pointer. */ void __init sev_snp_cpuid_init_virtual(void) { /* * sev_snp_cpuid_init() already did the initial parsing of bootparams * and initial setup. If that didn't enable the feature then don't try * to enable it here. */ if (!sev_snp_cpuid_active()) return; /* * Either boot_params/EFI advertised the feature even though SNP isn't * enabled, or something else went wrong. Bail out. */ if (!sev_feature_enabled(SEV_SNP)) sev_es_terminate(1, GHCB_TERM_CPUID); cpuid_info = &cpuid_info_copy; } #endif Then the rest of the code just accesses cpuid_info directly as it does now. Would that be a reasonable approach for v6? > > -- > Regards/Gruss, > Boris. > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpeople.kernel.org%2Ftglx%2Fnotes-about-netiquette&data=04%7C01%7Cmichael.roth%40amd.com%7C464de4ea70544dc32ba108d9696de67a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637656743008963071%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=wYK2a%2FuHgw0%2FQJsCVCIpoaJxdT0XASMYUfHvmDcowXg%3D&reserved=0