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Hallyn" , Andi Kleen , Greg KH , Andrew Scull , Dave Hansen , "Dr. David Alan Gilbert" , James Bottomley , Tobin Feldman-Fitzthum , Jim Cadden , Daniele Buono , linux-coco@lists.linux.dev, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v5 4/4] docs: security: Add coco/efi_secret documentation Date: Thu, 18 Nov 2021 11:33:59 +0000 Message-Id: <20211118113359.642571-5-dovmurik@linux.ibm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211118113359.642571-1-dovmurik@linux.ibm.com> References: <20211118113359.642571-1-dovmurik@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: YjJ-wr7c-NLArkOHZ2vFJaxPh-Y4Anj_ X-Proofpoint-ORIG-GUID: Gyv5FU_GAGXKmmECFz_KincPtLYEmh5Q Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.0.607.475 definitions=2021-11-18_05,2021-11-17_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 phishscore=0 mlxlogscore=999 spamscore=0 suspectscore=0 impostorscore=0 adultscore=0 malwarescore=0 priorityscore=1501 mlxscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2111180067 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add documentation for the efi_secret module which allows access to Confidential Computing injected secrets. Signed-off-by: Dov Murik --- Documentation/security/coco/efi_secret.rst | 103 +++++++++++++++++++++ Documentation/security/coco/index.rst | 9 ++ Documentation/security/index.rst | 1 + 3 files changed, 113 insertions(+) create mode 100644 Documentation/security/coco/efi_secret.rst create mode 100644 Documentation/security/coco/index.rst diff --git a/Documentation/security/coco/efi_secret.rst b/Documentation/security/coco/efi_secret.rst new file mode 100644 index 000000000000..bb7acae22e90 --- /dev/null +++ b/Documentation/security/coco/efi_secret.rst @@ -0,0 +1,103 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========== +efi_secret +========== + +This document describes how Confidential Computing secret injection is handled +from the firmware to the operating system. + + +Introduction +============ + +Confidential Computing (coco) hardware such as AMD SEV (Secure Encrypted +Virtualization) allows guest owners to inject secrets into the VMs +memory without the host/hypervisor being able to read them. In SEV, +secret injection is performed early in the VM launch process, before the +guest starts running. + +The efi_secret kernel module allows userspace applications to access these +secrets via securityfs. + + +Secret data flow +================ + +The guest firmware may reserve a designated memory area for secret injection, +and publish its location (base GPA and length) in the EFI configuration table +under a ``LINUX_EFI_COCO_SECRET_AREA_GUID`` entry +(``adf956ad-e98c-484c-ae11-b51c7d336447``). This memory area should be marked +by the firmware as ``EFI_RESERVED_TYPE``, and therefore the kernel should not +be use it for its own purposes. + +During the VM's launch, the virtual machine manager may inject a secret to that +area. In AMD SEV and SEV-ES this is performed using the +``KVM_SEV_LAUNCH_SECRET`` command (see [amd-mem-enc]_). The strucutre of the +injected Guest Owner secret data should be a GUIDed table of secret values; the +binary format is described in ``drivers/virt/coco/efi_secret/efi_secret.c`` +under "Structure of the EFI secret area". + +On kernel start, the kernel's EFI driver saves the location of the secret +memory (taken from the EFI configuration table) in the ``efi.coco_secret`` +field. + +When a userspace application needs to access the secrets inside the guest VM, +it loads the efi_secret kernel module (``CONFIG_EFI_SECRET=m``) which exposes +the secrets via securityfs. The details of the efi_secret filesystem interface +are in [efi-secret-abi]_. + + + +Application usage example +========================= + +Consider a guest performing computations on encrypted files. The Guest Owner +provides the decryption key (= secret) using the secret injection mechanism. +The guest application reads the secret from the efi_secret filesystem and +proceeds to decrypt the files into memory and then performs the needed +computations on the content. + +In this example, the host can't read the files from the disk image +because they are encrypted. Host can't read the decryption key because +it is passed using the secret injection mechanism (= secure channel). +Host can't read the decrypted content from memory because it's a +confidential (memory-encrypted) guest. + +Here is a simple example for usage of the efi_secret module in a guest +to which an EFI secret area with 4 secrets was injected during launch:: + + # modprobe efi_secret + # ls -la /sys/kernel/security/coco/efi_secret + total 0 + drwxr-xr-x 2 root root 0 Jun 28 11:54 . + drwxr-xr-x 3 root root 0 Jun 28 11:54 .. + -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b + -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6 + -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2 + -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910 + + # xxd /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910 + 00000000: 7468 6573 652d 6172 652d 7468 652d 6b61 these-are-the-ka + 00000010: 7461 2d73 6563 7265 7473 0001 0203 0405 ta-secrets...... + 00000020: 0607 .. + + # rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910 + + # ls -la /sys/kernel/security/coco/efi_secret + total 0 + drwxr-xr-x 2 root root 0 Jun 28 11:55 . + drwxr-xr-x 3 root root 0 Jun 28 11:54 .. + -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b + -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6 + -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2 + + +References +========== + +See [sev-api-spec]_ for more info regarding SEV ``LAUNCH_SECRET`` operation. + +.. [amd-mem-enc] :ref:`Documentation/virt/kvm/amd-memory-encryption ` +.. [efi-secret-abi] :ref:`Documentation/ABI/testing/securityfs-coco-efi_secret ` +.. [sev-api-spec] https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf diff --git a/Documentation/security/coco/index.rst b/Documentation/security/coco/index.rst new file mode 100644 index 000000000000..56b803d4b33e --- /dev/null +++ b/Documentation/security/coco/index.rst @@ -0,0 +1,9 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================================== +Confidential Computing documentation +==================================== + +.. toctree:: + + efi_secret diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst index 16335de04e8c..d4ef543825a7 100644 --- a/Documentation/security/index.rst +++ b/Documentation/security/index.rst @@ -17,3 +17,4 @@ Security Documentation tpm/index digsig landlock + coco -- 2.25.1