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From: Brijesh Singh <brijesh.singh@amd.com>
To: Dave Hansen <dave.hansen@intel.com>,
	Andy Lutomirski <luto@amacapital.net>
Cc: brijesh.singh@amd.com, x86@kernel.org,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	tglx@linutronix.de, bp@alien8.de, jroedel@suse.de,
	Thomas.Lendacky@amd.com, pbonzini@redhat.com, mingo@redhat.com,
	rientjes@google.com, seanjc@google.com, peterz@infradead.org,
	hpa@zytor.com, tony.luck@intel.com
Subject: Re: [PATCH Part2 RFC v2 10/37] x86/fault: Add support to handle the RMP fault for kernel address
Date: Tue, 4 May 2021 07:31:20 -0500	[thread overview]
Message-ID: <af581395-1322-a668-d5f3-3784bbfd6c9b@amd.com> (raw)
In-Reply-To: <b723e0dd-7af1-37b3-6553-e9ef4802dac8@intel.com>


On 5/3/21 2:43 PM, Dave Hansen wrote:
> On 5/3/21 12:41 PM, Brijesh Singh wrote:
>> Sure, I will look into all the drivers which do a walk plus kmap to make
>> sure that they fail instead of going into the fault path. Should I drop
>> this patch or keep it just in the case we miss something?
> I think you should drop it, and just ensure that the existing page fault
> oops code can produce a coherent, descriptive error message about what
> went wrong.

A malicious guest could still trick the host into accessing a guest
private page unless we make sure that host kernel *never* does kmap() on
GPA. The example I was thinking is:

1. Guest provides a GPA to host.

2. Host queries the RMP table and finds that GPA is shared and allows
the kmap() to happen.

3. Guest later changes the page to private.

4. Host write to mapped address will trigger a page-fault.

KVM provides kvm_map_gfn(), kvm_vcpu_map() to map a GPA; these APIs will
no longer be safe to be used. In addition, some shared pages are
registered once by the guest and KVM updates the contents of the page on
vcpu enter (e.g, CPU steal time).

IMHO, we should add the RMP table check before kmap'ing GPA but still
keep this patch to mitigate the cases where a malicious guest changes
the page state after the kmap().

-Brijesh



  reply	other threads:[~2021-05-04 12:31 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-30 12:37 [PATCH Part2 RFC v2 00/37] Add AMD Secure Nested Paging (SEV-SNP) Hypervisor Support Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 01/37] KVM: SVM: Add support to handle AP reset MSR protocol Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 02/37] KVM: SVM: Provide the Hypervisor Feature support VMGEXIT Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 03/37] KVM: SVM: Increase the GHCB protocol version Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 04/37] x86/cpufeatures: Add SEV-SNP CPU feature Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 05/37] x86/sev: Add the host SEV-SNP initialization support Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 06/37] x86/sev: Add RMP entry lookup helpers Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 07/37] x86/sev: Add helper functions for RMPUPDATE and PSMASH instruction Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 08/37] x86/sev: Split the physmap when adding the page in RMP table Brijesh Singh
2021-05-03 15:07   ` Peter Zijlstra
2021-05-03 15:15   ` Andy Lutomirski
2021-05-03 15:41     ` Dave Hansen
2021-05-07 11:28       ` Vlastimil Babka
2021-04-30 12:37 ` [PATCH Part2 RFC v2 09/37] x86/traps: Define RMP violation #PF error code Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 10/37] x86/fault: Add support to handle the RMP fault for kernel address Brijesh Singh
2021-05-03 14:44   ` Dave Hansen
2021-05-03 15:03     ` Andy Lutomirski
2021-05-03 15:49       ` Brijesh Singh
2021-05-03 15:37     ` Brijesh Singh
2021-05-03 16:15       ` Dave Hansen
2021-05-03 17:19         ` Brijesh Singh
2021-05-03 17:31           ` Brijesh Singh
2021-05-03 17:40           ` Andy Lutomirski
2021-05-03 19:41             ` Brijesh Singh
2021-05-03 19:43               ` Dave Hansen
2021-05-04 12:31                 ` Brijesh Singh [this message]
2021-05-04 14:33                   ` Dave Hansen
2021-05-04 15:16                     ` Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 11/37] x86/fault: Add support to handle the RMP fault for user address Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 12/37] crypto:ccp: Define the SEV-SNP commands Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 13/37] crypto: ccp: Add support to initialize the AMD-SP for SEV-SNP Brijesh Singh
2021-04-30 12:37 ` [PATCH Part2 RFC v2 14/37] crypto: ccp: Shutdown SNP firmware on kexec Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 15/37] crypto:ccp: Provide APIs to issue SEV-SNP commands Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 16/37] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled Brijesh Singh
2021-05-10 18:23   ` Peter Gonda
2021-05-10 20:07     ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 17/37] crypto: ccp: Handle the legacy SEV command " Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 18/37] KVM: SVM: make AVIC backing, VMSA and VMCB memory allocation SNP safe Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 19/37] KVM: SVM: Add initial SEV-SNP support Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 20/37] KVM: SVM: define new SEV_FEATURES field in the VMCB Save State Area Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 21/37] KVM: SVM: Add KVM_SNP_INIT command Brijesh Singh
2021-05-06 20:25   ` Peter Gonda
2021-05-06 22:29     ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 22/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_START command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 23/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_UPDATE command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 24/37] KVM: SVM: Reclaim the guest pages when SEV-SNP VM terminates Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 25/37] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 26/37] KVM: X86: Add kvm_x86_ops to get the max page level for the TDP Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 27/37] KVM: X86: Introduce kvm_mmu_map_tdp_page() for use by SEV Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 28/37] KVM: X86: Introduce kvm_mmu_get_tdp_walk() for SEV-SNP use Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 29/37] KVM: X86: Define new RMP check related #NPF error bits Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 30/37] KVM: X86: update page-fault trace to log the 64-bit error code Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 31/37] KVM: SVM: Add support to handle GHCB GPA register VMGEXIT Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 32/37] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT Brijesh Singh
2021-05-10 17:30   ` Peter Gonda
2021-05-10 17:51     ` Brijesh Singh
2021-05-10 19:59       ` Peter Gonda
2021-05-10 20:50         ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 33/37] KVM: SVM: Add support to handle " Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 34/37] KVM: X86: Export the kvm_zap_gfn_range() for the SNP use Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 35/37] KVM: SVM: Add support to handle the RMP nested page fault Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 36/37] KVM: SVM: Provide support for SNP_GUEST_REQUEST NAE event Brijesh Singh
2021-05-10 18:57   ` Peter Gonda
2021-05-10 20:14     ` Brijesh Singh
2021-05-10 21:17       ` Sean Christopherson
2021-05-11 18:34         ` Brijesh Singh
2021-04-30 12:38 ` [PATCH Part2 RFC v2 37/37] KVM: SVM: Advertise the SEV-SNP feature support Brijesh Singh

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