On 12/04/2022 13:04, Ard Biesheuvel wrote: > On Tue, 12 Apr 2022 at 12:03, Dov Murik <dovmurik@xxxxxxxxxxxxx> wrote: >> >> >> >> On 01/04/2022 0:56, Dov Murik wrote: >>> 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. >>> >>> OVMF already reserves designated area for secret injection (in its >>> AmdSev package; see edk2 commit 01726b6d23d4 "OvmfPkg/AmdSev: Expose the >>> Sev Secret area using a configuration table" [1]), but the secrets were >>> not available in the guest kernel. >>> >>> The patch series keeps the address of the EFI-provided memory for >>> injected secrets, and exposes the secrets to userspace via securityfs >>> using a new efi_secret kernel module. The module is autoloaded (by the >>> EFI driver) if the secret area is populated. >>> >>> The first patch in EFI keeps the address of the secret area as passed in >>> the EFI configuration table. The second patch introduces the new >>> efi_secret module that exposes the content of the secret entries as >>> securityfs files, and allows clearing out secrets with a file unlink >>> interface. The third patch auto-loads the efi_secret module during >>> startup if the injected secrets area is populated. The last patch >>> documents the data flow of confidential computing secret injection. >>> >>> As a 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. >>> >>> This has been tested with AMD SEV and SEV-ES guests, but the kernel side >>> of handling the secret area has no SEV-specific dependencies, and >>> therefore might be usable (perhaps with minor changes) for any >>> confidential computing hardware that can publish the secret area via the >>> standard EFI config table entry. >>> >>> To enable this functionality, set CONFIG_EFI_SECRET=m when building the >>> guest kernel. >>> >>> 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: >>> >>> ... >>> [ 0.000000] efi: EFI v2.70 by EDK II >>> [ 0.000000] efi: CocoSecret=0x7f222680 SMBIOS=0x7f541000 ACPI=0x7f77e000 ACPI 2.0=0x7f77e014 MEMATTR=0x7ea16418 >>> ... >>> [ 1.127627] Run /init as init process >>> Loading, please wait... >>> Starting version 245.4-4ubuntu3.15 >>> ... >>> [ 0.763204] efi_secret efi_secret.0: Created 4 entries in securityfs secrets/coco >>> ... >>> >>> # ls -la /sys/kernel/security/secrets/coco >>> 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 >>> >>> # hd /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910 >>> 00000000 74 68 65 73 65 2d 61 72 65 2d 74 68 65 2d 6b 61 |these-are-the-ka| >>> 00000010 74 61 2d 73 65 63 72 65 74 73 00 01 02 03 04 05 |ta-secrets......| >>> 00000020 06 07 |..| >>> 00000022 >>> >>> # rm /sys/kernel/security/secrets/coco/e6f5a162-d67f-4750-a67c-5d065f2a9910 >>> >>> # ls -la /sys/kernel/security/secrets/coco >>> 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 >>> >>> >>> [1] https://github.com/tianocore/edk2/commit/01726b6d23d4 >>> >>> >>> --- >>> >>> v9 changes: >>> - Change the module into a platform driver (thanks Ard) >>> - Remove special auto-loading code in efi; instead register a platform >>> device (udev will load the efi_secret module) (thanks Ard) >>> - Change logging in the efi_secret module to dev_err() etc. >>> - efi_secret: first check that the secret area header is valid; only then start >>> creating securityfs dirs. >>> >>> v8: https://lore.kernel.org/linux-coco/20220228114254.1099945-1-dovmurik@xxxxxxxxxxxxx/ >>> v8 changes: >>> - Change path of filesystem to <securityfs>/secrets/coco and fix the >>> documentation accordingly (Thanks Gerd, Matthew) >>> - Remove patch 2/5 (of v7) because the latest OVMF release (edk2-stable202202) >>> already contains the fix to mark the launch secret page as EFI_RESERVED_TYPE. >>> >>> v7: https://lore.kernel.org/linux-coco/20220201124413.1093099-1-dovmurik@xxxxxxxxxxxxx/ >>> v7 changes: >>> - Improve description of efi_secret module in Kconfig. >>> - Fix sparse warnings on pointer address space mismatch >>> (Reported-by: kernel test robot <lkp@xxxxxxxxx>) >>> >>> v6: https://lore.kernel.org/linux-coco/20211129114251.3741721-1-dovmurik@xxxxxxxxxxxxx/ >>> v6 changes: >>> - Autoload the efi_secret module if the secret area is populated >>> (thanks Greg KH). >>> - efi_secret: Depend on X86_64 because we use ioremap_encrypted() which >>> is only defined for this arch. >>> - efi_secret.c: Remove unneeded tableheader_guid local variable. >>> - Documentation fixes. >>> >>> v5: https://lore.kernel.org/linux-coco/20211118113359.642571-1-dovmurik@xxxxxxxxxxxxx/ >>> v5 changes: >>> - Simplify EFI code: instead of copying the secret area, the firmware >>> marks the secret area as EFI_RESERVED_TYPE, and then the uefi_init() >>> code just keeps the pointer as it appears in the EFI configuration >>> table. The use of reserved pages is similar to the AMD SEV-SNP >>> patches for handling SNP-Secrets and SNP-CPUID pages. >>> - In order to handle OVMF releases out there which mark the >>> confidential computing secrets page as EFI_BOOT_SERVICES_DATA, add >>> efi/libstub code that detects this and fixes the E820 map to reserve >>> this page. >>> - In the efi_secret module code, map the secrets page using >>> ioremap_encrypted (again, similar to the AMD SEV-SNP guest patches >>> for accessing SNP-Secrets and SNP-CPUID pages). >>> - Add documentation in Documentation/security/coco/efi_secret. >>> >>> v4: https://lore.kernel.org/linux-coco/20211020061408.3447533-1-dovmurik@xxxxxxxxxxxxx/ >>> v4 changes: >>> - Guard all the new EFI and efi-stub code (patches 1+2) with #ifdef >>> CONFIG_EFI_COCO_SECRET (thanks Greg KH). Selecting >>> CONFIG_EFI_SECRET=m (patch 3) will enable the EFI parts as well. >>> - Guard call to clflush_cache_range() with #ifdef CONFIG_X86 >>> (Reported-by: kernel test robot <lkp@xxxxxxxxx>) >>> >>> v3: https://lore.kernel.org/linux-coco/20211014130848.592611-1-dovmurik@xxxxxxxxxxxxx/ >>> v3 changes: >>> - Rename the module to efi_secret >>> - Remove the exporting of clean_cache_range >>> - Use clflush_cache_range in wipe_memory >>> - Document function wipe_memory >>> - Initialize efi.coco_secret to EFI_INVALID_TABLE_ADDR to correctly detect >>> when there's no secret area published in the EFI configuration tables >>> >>> v2: https://lore.kernel.org/linux-coco/20211007061838.1381129-1-dovmurik@xxxxxxxxxxxxx >>> v2 changes: >>> - Export clean_cache_range() >>> - When deleteing a secret, call clean_cache_range() after explicit_memzero >>> - Add Documentation/ABI/testing/securityfs-coco-sev_secret >>> >>> v1: https://lore.kernel.org/linux-coco/20210809190157.279332-1-dovmurik@xxxxxxxxxxxxx/ >>> >>> RFC: https://lore.kernel.org/linux-coco/20210628183431.953934-1-dovmurik@xxxxxxxxxxxxx/ >>> >>> >>> >>> Dov Murik (4): >>> efi: Save location of EFI confidential computing area >>> virt: Add efi_secret module to expose confidential computing secrets >>> efi: Register efi_secret platform device if EFI secret area is >>> declared >>> docs: security: Add secrets/coco documentation >>> >> >> >> This series has Reviewed-by tags on all patches (though, as I mentioned, >> there's a missing #ifdef in patch 3). >> >> Ard, are you going to take this through the EFI tree? >> >> Should I resend the series with the fix for patch 3? >> > > Yes, please send a final version with all tags in place etc, and I > will queue it up. > Great! Thank you, I'll do that shortly. -Dov
