From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mx.groups.io with SMTP id smtpd.web08.6811.1606809926927828566 for ; Tue, 01 Dec 2020 00:05:27 -0800 Authentication-Results: mx.groups.io; dkim=missing; spf=pass (domain: arm.com, ip: 217.140.110.172, mailfrom: ard.biesheuvel@arm.com) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8890B1042; Tue, 1 Dec 2020 00:05:26 -0800 (PST) Received: from [192.168.1.81] (unknown [10.37.8.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BA0E53F23F; Tue, 1 Dec 2020 00:05:22 -0800 (PST) Subject: Re: [PATCH v3 0/6] SEV Encrypted Boot for Ovmf To: James Bottomley , devel@edk2.groups.io Cc: dovmurik@linux.vnet.ibm.com, Dov.Murik1@il.ibm.com, ashish.kalra@amd.com, brijesh.singh@amd.com, tobin@ibm.com, david.kaplan@amd.com, jon.grimm@amd.com, thomas.lendacky@amd.com, frankeh@us.ibm.com, "Dr . David Alan Gilbert" , Laszlo Ersek , Jordan Justen References: <20201130202819.3910-1-jejb@linux.ibm.com> From: "Ard Biesheuvel" Message-ID: <2f0c10ac-d4b1-0873-0ef2-aeeea9b0d001@arm.com> Date: Tue, 1 Dec 2020 09:05:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201130202819.3910-1-jejb@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit On 11/30/20 9:28 PM, James Bottomley wrote: > v3: > > - More grub and boot stripping (I think I got everything out, but > there may be something that strayed in the boot panic resolution). > - grub.sh tidy up with tabs->spaces. > - Move the reset vector GUIDisation patch to the front so it can be > applied independently > - Update the .dsc and .fdf files for variable policy > > v2: > > - Strip more out of AmdSev image (networking, secure boot, smm) > - give sev reset block a generic table guid and use it for boot secret area > - separate secret patches and make grub script more robust > - Add copyrights and fix formatting issues > > v1: > > Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3077 > > This patch series is modelled on the structure of the Bhyve patches > for Ovmf, since it does somewhat similar things. This patch series > creates a separate build for an AmdSev OVMF.fd that does nothing > except combine with grub and boot straight through the internal grub > to try to mount an encrypted volume. > This all looks reasonable to me, although I defer to Laszlo when it comes to assessing the impact on maintainability of other platforms under OvmfPkg. Acked-by: Ard Biesheuvel Is there any point to keeping the TPM bits in the AmdSev platform? Or are these completely orthogonal? If there is no meaningful way [yet] to plumb these together, it might be better to just rip that out entirely so people don't make assumptions. > Concept: SEV Secure Encrypted Images > ==================================== > > The SEV patches in Linux and OVMF allow for the booting of SEV VMs in > an encrypted state, but don't really show how this could be done with > an encrypted image. Since the key used to decrypt the image must be > maintained within the SEV encryption envelope, encrypted QCOW is not > an option because the key would then have to be known to QEMU which is > outside the encryption envelope. The proposal here is that an > encrypted image should be a QCOW image consisting of two partitions, > the normal unencrypted EFI partition (Identifying it as an OVMF > bootable image) and a luks encrypted root partition. The kernel would > be inside the encrypted root in the /boot directory. The secret > injected securely through QEMU is extracted by OVMF and passed to grub > which uses it to mount the encrypted root and boot the kernel > normally. The creator of the secret bundle must be satisfied with the > SEV attestation before the secret is constructed. Unfortunately, the > SEV attestation can only be on the first QEMU firmware volume and > nothing else, so this patch series builds grub itself into a firmware > volume and places it inside OVMF so that the entire boot system can be > attested. In a normal OVMF KVM system, the variable store is on the > second flash volume (which is read/write). Unfortunately, this > mutable configuration provided by the variables is outside the > attestation envelope and can significantly alter the boot path, > possibly leading to secret leak, so encrypted image boot should only > be done with the OVMF.fd that combines both the code and variables. > the OVMF.fd is constructed so that it becomes impossible to interrupt > the boot sequence after attestation and the system will either boot > the image or fail. The boot sequence runs the grub.efi embedded in the > OVMF firmware volume so the encrypted image owner knows their own > version of grub is the only one that will boot before injecting the > secret. Note this boot path actually ignores the unencrypted EFI > partition. However, as part of this design, the encrypted image may be > booted by a standard OVMF KVM boot and in that case, the user will > have to type the encryption password. This standard boot will be > insecure but it might be used by the constructor of the encrypted > images on their own private laptop, for instance. The standard boot > path will use the unencrypted EFI partition. > > Patches Required Outside of OVMF > ================================ > > There is a patch set to grub which allows it to extract the SEV secret > area from the configuration table and use the secret as a password to > do a luks crypto mount of root (this is the sevsecret grub module): > > https://lists.gnu.org/archive/html/grub-devel/2020-11/msg00078.html > > There is also a patch to qemu which allows it to search through the > OVMF.fd and find the SEV secret area which is now described inside the > Reset Vector using the existing SEV_ES reset block. This area is the > place QEMU will inject the encrypted SEV secret bundle. > > Security of the System > ====================== > > Since Grub is now part of the attested OVMF.fd bundle, the VM owner > knows absolutely that it will proceed straight to partition decryption > inside the attested code and boot the kernel off the encrypted > partition. Even if a different QCOW image is substituted, the boot > will fail without revealing the secret because the system is designed > to fail hard in that case and because the secret is always contained > within the encrypted envelope it should be impossible for the cloud > operator to obtain it even if they can pause the boot and examine the > machine memory. > > Putting it All Together > ======================= > > This is somewhat hard. You must first understand how to boot a QEMU > system so as to have the VM pause after firmware loading (-S option) > and use the qmp port to request an attestation. Only if the > attestation corresponds to the expected sha256sum of OVMF.fd should > the secret bundle be constructed and injected using qmp. The tools > for constructing the secret bundle are in > > https://github.com/AMDESE/sev-tool/ > > James > > --- > > James Bottomley (6): > OvmfPkg/ResetVector: convert SEV-ES Reset Block structure to be GUIDed > OvmfPkg/Amdsev: Base commit to build encrypted boot specific OVMF > OvmfPkg/AmdSev: add Grub Firmware Volume Package > OvmfPkg: create a SEV secret area in the AmdSev memfd > OvmfPkg/AmdSev: assign and protect the Sev Secret area > OvmfPkg/AmdSev: Expose the Sev Secret area using a configuration table > > OvmfPkg/OvmfPkg.dec | 8 + > OvmfPkg/AmdSev/AmdSevX64.dsc | 844 ++++++++++ > OvmfPkg/AmdSev/AmdSevX64.fdf | 456 +++++ > OvmfPkg/AmdSev/Grub/Grub.inf | 39 + > OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf | 37 + > OvmfPkg/AmdSev/SecretPei/SecretPei.inf | 35 + > .../PlatformBootManagerLibGrub.inf | 71 + > OvmfPkg/ResetVector/ResetVector.inf | 4 + > OvmfPkg/Include/Guid/SevLaunchSecret.h | 28 + > .../PlatformBootManagerLibGrub/BdsPlatform.h | 175 ++ > OvmfPkg/AmdSev/SecretDxe/SecretDxe.c | 26 + > OvmfPkg/AmdSev/SecretPei/SecretPei.c | 25 + > .../PlatformBootManagerLibGrub/BdsPlatform.c | 1482 +++++++++++++++++ > .../PlatformBootManagerLibGrub/PlatformData.c | 214 +++ > OvmfPkg/AmdSev/Grub/.gitignore | 1 + > OvmfPkg/AmdSev/Grub/grub.cfg | 46 + > OvmfPkg/AmdSev/Grub/grub.sh | 93 ++ > OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm | 70 +- > OvmfPkg/ResetVector/ResetVector.nasmb | 2 + > 19 files changed, 3645 insertions(+), 11 deletions(-) > create mode 100644 OvmfPkg/AmdSev/AmdSevX64.dsc > create mode 100644 OvmfPkg/AmdSev/AmdSevX64.fdf > create mode 100644 OvmfPkg/AmdSev/Grub/Grub.inf > create mode 100644 OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf > create mode 100644 OvmfPkg/AmdSev/SecretPei/SecretPei.inf > create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformBootManagerLibGrub.inf > create mode 100644 OvmfPkg/Include/Guid/SevLaunchSecret.h > create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.h > create mode 100644 OvmfPkg/AmdSev/SecretDxe/SecretDxe.c > create mode 100644 OvmfPkg/AmdSev/SecretPei/SecretPei.c > create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/BdsPlatform.c > create mode 100644 OvmfPkg/Library/PlatformBootManagerLibGrub/PlatformData.c > create mode 100644 OvmfPkg/AmdSev/Grub/.gitignore > create mode 100644 OvmfPkg/AmdSev/Grub/grub.cfg > create mode 100644 OvmfPkg/AmdSev/Grub/grub.sh >