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References: <20210630125321.30278-1-brijesh.singh@amd.com> <20210630125321.30278-8-brijesh.singh@amd.com>
In-Reply-To: <20210630125321.30278-8-brijesh.singh@amd.com>
From: "Erdem Aktas" <erdemaktas@google.com>
Date: Sat, 31 Jul 2021 01:44:56 -0700
Message-ID: <CAAYXXYz+C=B03Zi0OKNCHhbxk4EazYJnadHCfPVx1VuzrmLAsA@mail.gmail.com>
Subject: Re: [RFC PATCH v5 07/28] OvmfPkg/ResetVector: pre-validate the data pages used in SEC phase
To: Brijesh Singh <brijesh.singh@amd.com>
Cc: devel@edk2.groups.io, James Bottomley <jejb@linux.ibm.com>, Min Xu <min.m.xu@intel.com>, 
	Jiewen Yao <jiewen.yao@intel.com>, Tom Lendacky <thomas.lendacky@amd.com>, 
	Jordan Justen <jordan.l.justen@intel.com>, Ard Biesheuvel <ardb+tianocore@kernel.org>, 
	Laszlo Ersek <lersek@redhat.com>, Eric Dong <eric.dong@intel.com>, Ray Ni <ray.ni@intel.com>, 
	Rahul Kumar <rahul1.kumar@intel.com>, Michael D Kinney <michael.d.kinney@intel.com>, 
	Liming Gao <gaoliming@byosoft.com.cn>, Zhiguang Liu <zhiguang.liu@intel.com>, 
	Michael Roth <Michael.Roth@amd.com>
Content-Type: text/plain; charset="UTF-8"

On Wed, Jun 30, 2021 at 5:54 AM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> a) Enhance the OVMF reset vector code to validate the pages as described
>    above (go through step 2 - 3).
> OR
> b) Validate the pages during the guest creation time. The SEV firmware
>    provides a command which can be used by the VMM to validate the pages
>    without affecting the measurement of the launch.

Are you referring to the PAGE_TYPE_UNMEASURED? Does it not affect the
measurement , PAGE_INFO will be still measured, right?

> Approach #b seems much simpler; it does not require any changes to the
> OVMF reset vector code.

I am worried about verifying the measurement. I understand the secret
page and cpuid page being part of measurement because both of them are
mentioned in the AMD SNP SPEC but now we are introducing a new
parameters (all the 4KB page addresses between SNP_HV_VALIDATED_START
and SNP_HV_VALIDATED_END) that VM owner needs to know to calculate the
measurement and verify the attestation.

Sorry if I am overthinking or missing something here.

-Erdem