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Received: from SN6PR12MB2767.namprd12.prod.outlook.com (2603:10b6:805:75::23) by SN7PR12MB8148.namprd12.prod.outlook.com (2603:10b6:806:351::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5834.15; Wed, 23 Nov 2022 18:32:25 +0000 Received: from SN6PR12MB2767.namprd12.prod.outlook.com ([fe80::395:21e6:abfd:7894]) by SN6PR12MB2767.namprd12.prod.outlook.com ([fe80::395:21e6:abfd:7894%6]) with mapi id 15.20.5834.015; Wed, 23 Nov 2022 18:32:24 +0000 Message-ID: <57c77407-d0bc-5e74-490b-f604b4f97691@amd.com> Date: Wed, 23 Nov 2022 12:32:19 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1 Subject: Re: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled Content-Language: en-US To: Borislav Petkov Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, michael.roth@amd.com, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, dgilbert@redhat.com, jarkko@kernel.org References: <3a51840f6a80c87b39632dc728dbd9b5dd444cd7.1655761627.git.ashish.kalra@amd.com> <380c9748-1c86-4763-ea18-b884280a3b60@amd.com> <13bd73b6-592c-66c4-cd42-0913380da745@amd.com> From: "Kalra, Ashish" In-Reply-To: Content-Type: text/plain; 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> > ... > > for (i = 0; i < npages; i++) { > pfn = page_to_pfn(inpages[i]); > > ... > > ret = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_UPDATE, &data, error); > if (ret) { > /* > * If the command failed then need to reclaim the page. > */ > snp_page_reclaim(pfn); > > and here it would leak the pages if it cannot reclaim them. > > Now how did you get those? > > Through params.uaddr and params.len which come from userspace: > > if (copy_from_user(¶ms, (void __user *)(uintptr_t)argp->data, sizeof(params))) > return -EFAULT; > > > Now, think about it, can userspace be trusted? > > Exactly. > > Yeah, yeah, I see it does is_hva_registered() but userspace can just as > well supply the wrong region which fits. Yes, that's right. Also, before sev_issue_cmd() above, there is a call to rmp_make_private() to make these pages transition to firmware state before we issue the LAUNCH_UPDATE command as below: ret = rmp_make_private(pfn, gfn << PAGE_SHIFT, level, sev_get_asid(kvm), true); if (ret) { ret = -EFAULT; goto e_unpin; } ... ret = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_UPDATE, &data, error); So in case, the userspace provided an invalid/incorrect range, this transition would have failed and there would not have been a need to do any reclaim, so there are no pages leaked here. This is also the reason why we need to reclaim pages if the subsequent LAUNCH_UPDATE command fails, as now the pages are in F/W state because of the rmp_make_private() call and they are now unsafe to be used by the host. > >> In such a case the kernel panic is justifiable, > > So userspace can supply whatever it wants and you'd panic? > > You surely don't mean that. > No, we don't want to do that. >> but again if incorrect addresses are supplied, the failure will happen >> at the initial stage of transitioning these pages to firmware state >> and there is no need to reclaim. This is the case i mentioned above, rmp_make_private() before the firmware command is the initial stage of transitioning the pages to firmware state before issuing the firmware command. > > See above. > >> Or, otherwise dump a warning and let the pages not be freed/returned >> back to the page allocator. >> >> It is either innocent pages or kernel panic or an innocent host >> process crash (these are the choices to make). > > No, it is make the kernel as resilient as possible. Which means, no > panic, add the pages to a not-to-be-used-anymore list and scream loudly > with warning messages when it must leak pages so that people can fix the > issue. > > Ok? > Right, yes, i totally agree. So now we are adding these pages to an internal not-to-be-used-anymore list and printing warnings and ensuring no panics as we don't allow these pages to be released back to the page allocator. Thanks, Ashish