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Date: Thu, 23 Sep 2021 17:23:55 -0500 From: Brijesh Singh <brijesh.singh@....com> To: "Dr. David Alan Gilbert" <dgilbert@...hat.com> Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org, linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>, Tom Lendacky <thomas.lendacky@....com>, "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, David Rientjes <rientjes@...gle.com>, Dov Murik <dovmurik@...ux.ibm.com>, Tobin Feldman-Fitzthum <tobin@....com>, Borislav Petkov <bp@...en8.de>, Michael Roth <michael.roth@....com>, Vlastimil Babka <vbabka@...e.cz>, "Kirill A . Shutemov" <kirill@...temov.name>, Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com, marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com Subject: Re: [PATCH Part2 v5 21/45] KVM: SVM: Make AVIC backing, VMSA and VMCB memory allocation SNP safe On 9/23/21 1:39 PM, Dr. David Alan Gilbert wrote: > * Brijesh Singh (brijesh.singh@....com) wrote: >> On 9/22/21 1:55 PM, Dr. David Alan Gilbert wrote: >>> * Brijesh Singh (brijesh.singh@....com) wrote: >>>> Implement a workaround for an SNP erratum where the CPU will incorrectly >>>> signal an RMP violation #PF if a hugepage (2mb or 1gb) collides with the >>>> RMP entry of a VMCB, VMSA or AVIC backing page. >>>> >>>> When SEV-SNP is globally enabled, the CPU marks the VMCB, VMSA, and AVIC >>>> backing pages as "in-use" in the RMP after a successful VMRUN. This is >>>> done for _all_ VMs, not just SNP-Active VMs. >>> Can you explain what 'globally enabled' means? >> This means that SNP is enabled inĀ host SYSCFG_MSR.Snp=1. Once its >> enabled then RMP checks are enforced. >> >> >>> Or more specifically, can we trip this bug on public hardware that has >>> the SNP enabled in the bios, but no SNP init in the host OS? >> Enabling the SNP support on host is 3 step process: >> >> step1 (bios): reserve memory for the RMP table. >> >> step2 (host): initialize the RMP table memory, set the SYSCFG msr to >> enable the SNP feature >> >> step3 (host): call the SNP_INIT to initialize the SNP firmware (this is >> needed only if you ever plan to launch SNP guest from this host). >> >> The "SNP globally enabled" means the step 1 to 2. The RMP checks are >> enforced as soon as step 2 is completed. > So I think that means we don't need to backport this to older kernels > that don't know about SNP but might run on SNP enabled hardware (1), since > those kernels won't do step2. Correct. thanks
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