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 is a quirk fix for older
firmwares didn't mark the secrets page as EFI_RESERVED_TYPE. The third
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 fourth 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:
# 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
[1] https://github.com/tianocore/edk2/commit/01726b6d23d4
---
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@linux.ibm.com/
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@linux.ibm.com/
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 [off-list ref])
v3: https://lore.kernel.org/linux-coco/20211014130848.592611-1-dovmurik@linux.ibm.com/
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@linux.ibm.com
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@linux.ibm.com/
RFC: https://lore.kernel.org/linux-coco/20210628183431.953934-1-dovmurik@linux.ibm.com/
Dov Murik (5):
efi: Save location of EFI confidential computing area
efi/libstub: Reserve confidential computing secret area
virt: Add efi_secret module to expose confidential computing secrets
efi: Load efi_secret module if EFI secret area is populated
docs: security: Add coco/efi_secret documentation
.../ABI/testing/securityfs-coco-efi_secret | 51 +++
Documentation/security/coco/efi_secret.rst | 102 ++++++
Documentation/security/coco/index.rst | 9 +
Documentation/security/index.rst | 1 +
arch/x86/platform/efi/efi.c | 3 +
drivers/firmware/efi/Kconfig | 16 +
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/coco.c | 58 +++
drivers/firmware/efi/efi.c | 6 +
drivers/firmware/efi/libstub/x86-stub.c | 28 ++
drivers/virt/Kconfig | 3 +
drivers/virt/Makefile | 1 +
drivers/virt/coco/efi_secret/Kconfig | 14 +
drivers/virt/coco/efi_secret/Makefile | 2 +
drivers/virt/coco/efi_secret/efi_secret.c | 337 ++++++++++++++++++
include/linux/efi.h | 10 +
16 files changed, 642 insertions(+)
create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
create mode 100644 Documentation/security/coco/efi_secret.rst
create mode 100644 Documentation/security/coco/index.rst
create mode 100644 drivers/firmware/efi/coco.c
create mode 100644 drivers/virt/coco/efi_secret/Kconfig
create mode 100644 drivers/virt/coco/efi_secret/Makefile
create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
base-commit: 42eb8fdac2fc5d62392dcfcf0253753e821a97b0
--
2.25.1
If the efi_secret module is built, register a late_initcall in the EFI
driver which checks whether the EFI secret area is available and
populated, and then requests to load the efi_secret module.
This will cause the <securityfs>/coco/efi_secret directory to appear in
guests into which secrets were injected; in other cases, the module is
not loaded.
Signed-off-by: Dov Murik <redacted>
---
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/coco.c | 58 ++++++++++++++++++++++++++++
drivers/virt/coco/efi_secret/Kconfig | 3 ++
3 files changed, 62 insertions(+)
create mode 100644 drivers/firmware/efi/coco.c
@@ -0,0 +1,102 @@+.. 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, in the EFI driver and the efi_secret+kernel module.+++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 [sev]_). 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 area+(taken from the EFI configuration table) in the ``efi.coco_secret`` field.+Later it checks if the secret area is populated: it maps the area and checks+whether its content begins with ``EFI_SECRET_TABLE_HEADER_GUID``+(``1e74f542-71dd-4d66-963e-ef4287ff173b``). If the secret area is populated,+the EFI driver will autoload the efi_secret kernel module, which exposes the+secretes to userspace applications 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::++ # 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.++..[sev] Documentation/virt/kvm/amd-memory-encryption.rst+..[efi-secret-abi] Documentation/ABI/testing/securityfs-coco-efi_secret+..[sev-api-spec] https://www.amd.com/system/files/TechDocs/55766_SEV-KM_API_Specification.pdf
The new efi_secret module exposes the confidential computing (coco)
EFI secret area via securityfs interface.
When the module is loaded (and securityfs is mounted, typically under
/sys/kernel/security), a "coco/efi_secret" directory is created in
securityfs. In it, a file is created for each secret entry. The name
of each such file is the GUID of the secret entry, and its content is
the secret data.
This allows applications running in a confidential computing setting to
read secrets provided by the guest owner via a secure secret injection
mechanism (such as AMD SEV's LAUNCH_SECRET command).
Removing (unlinking) files in the "coco/efi_secret" directory will zero
out the secret in memory, and remove the filesystem entry. If the
module is removed and loaded again, that secret will not appear in the
filesystem.
Signed-off-by: Dov Murik <redacted>
---
.../ABI/testing/securityfs-coco-efi_secret | 51 +++
drivers/virt/Kconfig | 3 +
drivers/virt/Makefile | 1 +
drivers/virt/coco/efi_secret/Kconfig | 11 +
drivers/virt/coco/efi_secret/Makefile | 2 +
drivers/virt/coco/efi_secret/efi_secret.c | 337 ++++++++++++++++++
6 files changed, 405 insertions(+)
create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
create mode 100644 drivers/virt/coco/efi_secret/Kconfig
create mode 100644 drivers/virt/coco/efi_secret/Makefile
create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
@@ -0,0 +1,51 @@+What: security/coco/efi_secret+Date: October 2021+Contact: Dov Murik <dovmurik@linux.ibm.com>+Description:+ Exposes confidential computing (coco) EFI secrets to+ userspace via securityfs.++ EFI can declare memory area used by confidential computing+ platforms (such as AMD SEV and SEV-ES) for secret injection by+ the Guest Owner during VM's launch. The secrets are encrypted+ by the Guest Owner and decrypted inside the trusted enclave,+ and therefore are not readable by the untrusted host.++ The efi_secret module exposes the secrets to userspace. Each+ secret appears as a file under <securityfs>/coco/efi_secret,+ where the filename is the GUID of the entry in the secrets+ table. This module is loaded automatically by the EFI driver+ if the EFI secret area is populated.++ Two operations are supported for the files: read and unlink.+ Reading the file returns the content of secret entry.+ Unlinking the file overwrites the secret data with zeroes and+ removes the entry from the filesystem. A secret cannot be read+ after it has been unlinked.++ For example, listing the available secrets::++ # modprobe efi_secret+ # ls -l /sys/kernel/security/coco/efi_secret+ -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++ Reading the secret data by reading a file::++ # cat /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910+ the-content-of-the-secret-data++ Wiping a secret by unlinking a file::++ # rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910+ # ls -l /sys/kernel/security/coco/efi_secret+ -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++ Note: The binary format of the secrets table injected by the+ Guest Owner is described in+ drivers/virt/coco/efi_secret/efi_secret.c under "Structure of+ the EFI secret area".
@@ -0,0 +1,337 @@+// SPDX-License-Identifier: GPL-2.0+/*+*efi_secretmodule+*+*Copyright(C)2021IBMCorporation+*Author:DovMurik<dovmurik@linux.ibm.com>+*/++/**+*DOC:efi_secret:AllowreadingEFIconfidentialcomputing(coco)secretarea+*viasecurityfsinterface.+*+*Whenthemoduleisloaded(andsecurityfsismounted,typicallyunder+*/sys/kernel/security),a"coco/efi_secret"directoryiscreatedin+*securityfs.Init,afileiscreatedforeachsecretentry.Thenameof+*eachsuchfileistheGUIDofthesecretentry,anditscontentisthe+*secretdata.+*/++#include<linux/seq_file.h>+#include<linux/fs.h>+#include<linux/kernel.h>+#include<linux/init.h>+#include<linux/module.h>+#include<linux/io.h>+#include<linux/security.h>+#include<linux/efi.h>+#include<asm/cacheflush.h>++#define EFI_SECRET_NUM_FILES 64++structefi_secret{+structdentry*coco_dir;+structdentry*fs_dir;+structdentry*fs_files[EFI_SECRET_NUM_FILES];+void__iomem*secret_data;+u64secret_data_len;+};++/*+*StructureoftheEFIsecretarea+*+*OffsetLength+*(bytes)(bytes)Usage+*-------------------+*016SecrettableheaderGUID(mustbe1e74f542-71dd-4d66-963e-ef4287ff173b)+*164Lengthofbytesoftheentiresecretarea+*+*2016Firstsecretentry'sGUID+*364Firstsecretentry'slengthinbytes(=16+4+x)+*40xFirstsecretentry'sdata+*+*40+x16Secondsecretentry'sGUID+*56+x4Secondsecretentry'slengthinbytes(=16+4+y)+*60+xySecondsecretentry'sdata+*+*(...andsoonforadditionalentries)+*+*TheGUIDofeachsecretentrydesignatestheusageofthesecretdata.+*/++/**+*structsecret_header-Headerofentiresecretarea;thisshouldbefollowed+*byinstancesofstructsecret_entry.+*@guid:MustbeEFI_SECRET_TABLE_HEADER_GUID+*@len:Lengthinbytesofentiresecretarea,includingheader+*/+structsecret_header{+efi_guid_tguid;+u32len;+}__attribute((packed));++/**+*structsecret_entry-Holdsonesecretentry+*@guid:Secret-specificGUID(orNULL_GUIDifthissecretentrywasdeleted)+*@len:Lengthofsecretentry,includingitsguidandlenfields+*@data:Thesecretdata(fullofzerosifthissecretentrywasdeleted)+*/+structsecret_entry{+efi_guid_tguid;+u32len;+u8data[];+}__attribute((packed));++staticsize_tsecret_entry_data_len(structsecret_entry*e)+{+returne->len-sizeof(*e);+}++staticstructefi_secretthe_efi_secret;++staticinlinestructefi_secret*efi_secret_get(void)+{+return&the_efi_secret;+}++staticintefi_secret_bin_file_show(structseq_file*file,void*data)+{+structsecret_entry*e=file->private;++if(e)+seq_write(file,e->data,secret_entry_data_len(e));++return0;+}+DEFINE_SHOW_ATTRIBUTE(efi_secret_bin_file);++/*+*Overwritememorycontentwithzeroes,andensurethatdirtycachelinesare+*actuallywrittenbacktomemory,toclearoutthesecret.+*/+staticvoidwipe_memory(void*addr,size_tsize)+{+memzero_explicit(addr,size);+#ifdef CONFIG_X86+clflush_cache_range(addr,size);+#endif+}++staticintefi_secret_unlink(structinode*dir,structdentry*dentry)+{+structefi_secret*s=efi_secret_get();+structinode*inode=d_inode(dentry);+structsecret_entry*e=(structsecret_entry*)inode->i_private;+inti;++if(e){+/* Zero out the secret data */+wipe_memory(e->data,secret_entry_data_len(e));+e->guid=NULL_GUID;+}++inode->i_private=NULL;++for(i=0;i<EFI_SECRET_NUM_FILES;i++)+if(s->fs_files[i]==dentry)+s->fs_files[i]=NULL;++/*+*securityfs_removetriestolockthedirectory'sinode,butwereach+*theunlinkcallbackwhenit'salreadylocked+*/+inode_unlock(dir);+securityfs_remove(dentry);+inode_lock(dir);++return0;+}++staticconststructinode_operationsefi_secret_dir_inode_operations={+.lookup=simple_lookup,+.unlink=efi_secret_unlink,+};++staticintefi_secret_map_area(void)+{+intret;+structefi_secret*s=efi_secret_get();+structlinux_efi_coco_secret_area*secret_area;++if(efi.coco_secret==EFI_INVALID_TABLE_ADDR){+pr_err("Secret area address is not available\n");+return-EINVAL;+}++secret_area=memremap(efi.coco_secret,sizeof(*secret_area),MEMREMAP_WB);+if(secret_area==NULL){+pr_err("Could not map secret area EFI config entry\n");+return-ENOMEM;+}+if(!secret_area->base_pa||secret_area->size<sizeof(structsecret_header)){+pr_err("Invalid secret area memory location (base_pa=0x%llx size=0x%llx)\n",+secret_area->base_pa,secret_area->size);+ret=-EINVAL;+gotounmap;+}++s->secret_data=ioremap_encrypted(secret_area->base_pa,secret_area->size);+if(s->secret_data==NULL){+pr_err("Could not map secret area\n");+ret=-ENOMEM;+gotounmap;+}++s->secret_data_len=secret_area->size;+ret=0;++unmap:+memunmap(secret_area);+returnret;+}++staticvoidefi_secret_securityfs_teardown(void)+{+structefi_secret*s=efi_secret_get();+inti;++for(i=(EFI_SECRET_NUM_FILES-1);i>=0;i--){+securityfs_remove(s->fs_files[i]);+s->fs_files[i]=NULL;+}++securityfs_remove(s->fs_dir);+s->fs_dir=NULL;++securityfs_remove(s->coco_dir);+s->coco_dir=NULL;++pr_debug("Removed efi_secret securityfs entries\n");+}++staticintefi_secret_securityfs_setup(void)+{+structefi_secret*s=efi_secret_get();+intret=0,i=0,bytes_left;+unsignedchar*ptr;+structsecret_header*h;+structsecret_entry*e;+structdentry*dent;+charguid_str[EFI_VARIABLE_GUID_LEN+1];++s->coco_dir=NULL;+s->fs_dir=NULL;+memset(s->fs_files,0,sizeof(s->fs_files));++dent=securityfs_create_dir("coco",NULL);+if(IS_ERR(dent)){+pr_err("Error creating coco securityfs directory entry err=%ld\n",PTR_ERR(dent));+returnPTR_ERR(dent);+}+s->coco_dir=dent;++dent=securityfs_create_dir("efi_secret",s->coco_dir);+if(IS_ERR(dent)){+pr_err("Error creating efi_secret securityfs directory entry err=%ld\n",+PTR_ERR(dent));+returnPTR_ERR(dent);+}+d_inode(dent)->i_op=&efi_secret_dir_inode_operations;+s->fs_dir=dent;++ptr=s->secret_data;+h=(structsecret_header*)ptr;+if(efi_guidcmp(h->guid,EFI_SECRET_TABLE_HEADER_GUID)){+pr_err("EFI secret area does not start with correct GUID\n");+ret=-EINVAL;+gotoerr_cleanup;+}+if(h->len<sizeof(*h)){+pr_err("EFI secret area reported length is too small\n");+ret=-EINVAL;+gotoerr_cleanup;+}+if(h->len>s->secret_data_len){+pr_err("EFI secret area reported length is too big\n");+ret=-EINVAL;+gotoerr_cleanup;+}++bytes_left=h->len-sizeof(*h);+ptr+=sizeof(*h);+while(bytes_left>=(int)sizeof(*e)&&i<EFI_SECRET_NUM_FILES){+e=(structsecret_entry*)ptr;+if(e->len<sizeof(*e)||e->len>(unsignedint)bytes_left){+pr_err("EFI secret area is corrupted\n");+ret=-EINVAL;+gotoerr_cleanup;+}++/* Skip deleted entries (which will have NULL_GUID) */+if(efi_guidcmp(e->guid,NULL_GUID)){+efi_guid_to_str(&e->guid,guid_str);++dent=securityfs_create_file(guid_str,0440,s->fs_dir,(void*)e,+&efi_secret_bin_file_fops);+if(IS_ERR(dent)){+pr_err("Error creating efi_secret securityfs entry\n");+ret=PTR_ERR(dent);+gotoerr_cleanup;+}++s->fs_files[i++]=dent;+}+ptr+=e->len;+bytes_left-=e->len;+}++pr_debug("Created %d entries in efi_secret securityfs\n",i);+return0;++err_cleanup:+efi_secret_securityfs_teardown();+returnret;+}++staticvoidefi_secret_unmap_area(void)+{+structefi_secret*s=efi_secret_get();++if(s->secret_data){+iounmap(s->secret_data);+s->secret_data=NULL;+s->secret_data_len=0;+}+}++staticint__initefi_secret_init(void)+{+intret;++ret=efi_secret_map_area();+if(ret)+returnret;++ret=efi_secret_securityfs_setup();+if(ret)+gotoerr_unmap;++returnret;++err_unmap:+efi_secret_unmap_area();+returnret;+}++staticvoid__exitefi_secret_exit(void)+{+efi_secret_securityfs_teardown();+efi_secret_unmap_area();+}++module_init(efi_secret_init);+module_exit(efi_secret_exit);++MODULE_DESCRIPTION("Confidential computing EFI secret area access");+MODULE_AUTHOR("IBM");+MODULE_LICENSE("GPL");
Confidential computing (coco) hardware such as AMD SEV (Secure Encrypted
Virtualization) allows a guest owner to inject secrets into the VMs
memory without the host/hypervisor being able to read them.
Firmware support for secret injection is available in OVMF, which
reserves a memory area for secret injection and includes a pointer to it
the in EFI config table entry LINUX_EFI_COCO_SECRET_TABLE_GUID.
If EFI exposes such a table entry, uefi_init() will keep a pointer to
the EFI config table entry in efi.coco_secret, so it can be used later
by the kernel (specifically drivers/virt/coco/efi_secret). It will also
appear in the kernel log as "CocoSecret=ADDRESS"; for example:
[ 0.000000] efi: EFI v2.70 by EDK II
[ 0.000000] efi: CocoSecret=0x7f22e680 SMBIOS=0x7f541000 ACPI=0x7f77e000 ACPI 2.0=0x7f77e014 MEMATTR=0x7ea0c018
The new functionality can be enabled with CONFIG_EFI_COCO_SECRET=y.
Signed-off-by: Dov Murik <redacted>
---
arch/x86/platform/efi/efi.c | 3 +++
drivers/firmware/efi/Kconfig | 16 ++++++++++++++++
drivers/firmware/efi/efi.c | 6 ++++++
include/linux/efi.h | 10 ++++++++++
4 files changed, 35 insertions(+)
Some older firmware declare the confidential computing secret area as
EFI_BOOT_SERVICES_DATA region. Fix this up by treating this memory
region as EFI_RESERVED_TYPE, as it should be.
If that memory region is already EFI_RESERVED_TYPE then this has no
effect on the E820 map.
Signed-off-by: Dov Murik <redacted>
---
drivers/firmware/efi/libstub/x86-stub.c | 28 +++++++++++++++++++++++++
1 file changed, 28 insertions(+)
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 is a quirk fix for older
firmwares didn't mark the secrets page as EFI_RESERVED_TYPE. The third
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 fourth 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:
# 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
[1] https://github.com/tianocore/edk2/commit/01726b6d23d4
---
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@linux.ibm.com/
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@linux.ibm.com/
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 [off-list ref])
v3: https://lore.kernel.org/linux-coco/20211014130848.592611-1-dovmurik@linux.ibm.com/
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@linux.ibm.com
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@linux.ibm.com/
RFC: https://lore.kernel.org/linux-coco/20210628183431.953934-1-dovmurik@linux.ibm.com/
Dov Murik (5):
efi: Save location of EFI confidential computing area
efi/libstub: Reserve confidential computing secret area
virt: Add efi_secret module to expose confidential computing secrets
efi: Load efi_secret module if EFI secret area is populated
docs: security: Add coco/efi_secret documentation
.../ABI/testing/securityfs-coco-efi_secret | 51 +++
Documentation/security/coco/efi_secret.rst | 102 ++++++
Documentation/security/coco/index.rst | 9 +
Documentation/security/index.rst | 1 +
arch/x86/platform/efi/efi.c | 3 +
drivers/firmware/efi/Kconfig | 16 +
drivers/firmware/efi/Makefile | 1 +
drivers/firmware/efi/coco.c | 58 +++
drivers/firmware/efi/efi.c | 6 +
drivers/firmware/efi/libstub/x86-stub.c | 28 ++
drivers/virt/Kconfig | 3 +
drivers/virt/Makefile | 1 +
drivers/virt/coco/efi_secret/Kconfig | 14 +
drivers/virt/coco/efi_secret/Makefile | 2 +
drivers/virt/coco/efi_secret/efi_secret.c | 337 ++++++++++++++++++
include/linux/efi.h | 10 +
16 files changed, 642 insertions(+)
create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
create mode 100644 Documentation/security/coco/efi_secret.rst
create mode 100644 Documentation/security/coco/index.rst
create mode 100644 drivers/firmware/efi/coco.c
create mode 100644 drivers/virt/coco/efi_secret/Kconfig
create mode 100644 drivers/virt/coco/efi_secret/Makefile
create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
base-commit: 42eb8fdac2fc5d62392dcfcf0253753e821a97b0
On Mon, Nov 29, 2021 at 11:42:46AM +0000, Dov Murik wrote:
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.
So maybe I don't understand the example properly or something's missing
but why can't the guest owner simply scp the secrets into the guest? Why
is this special thing needed?
The secret below says "...kata-secrets" so this sounds like
something-automated-containers-thing where they'd profit from getting
secrets automatically supplied to the guest. But I guess there you can
scp too...
So what am I missing?
Thx.
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
Hello Boris,
On 03/01/2022 20:59, Borislav Petkov wrote:
On Mon, Nov 29, 2021 at 11:42:46AM +0000, Dov Murik wrote:
quoted
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.
So maybe I don't understand the example properly or something's missing
but why can't the guest owner simply scp the secrets into the guest? Why
is this special thing needed?
If the Guest Owner chooses to inject secrets via scp, it needs
to be sure it is scp-ing to the correct VM - the one that has SEV
enabled and was measured at launch.
One way to achieve that would be to inject the guest's SSH private key
using the proposed efi_secret mechanism. This way the Guest Owner is
sure it is talking to the correct guest and not to some other VM that
was started by the untrusted cloud provider (say, with SEV disabled so
the cloud provider can steal its memory content).
The secret below says "...kata-secrets" so this sounds like
something-automated-containers-thing where they'd profit from getting
secrets automatically supplied to the guest. But I guess there you can
scp too...
Indeed this proposed efi_secret module is in use for enabling SEV
confidential containers using Kata containers [1], but there's nothing
specific in the current patch series about containers. The patch series
just exposes the launch-injected SEV secrets to userspace as virtual files
(under securityfs).
[1] https://github.com/confidential-containers/attestation-agent/tree/main/src/kbc_modules/offline_sev_kbc
So what am I missing?
It boils down to: the confidential guest needs to have access to a
secret which the untrusted host can't read, and which is essential for
the normal operation of the guest. This secret can be a decryption key,
an SSH private key, an API key to a Key Management system, etc. If a
malicious cloud provider tries to start that VM without a secret (or
with the wrong one), the actual workload that the guest is supposed to
run will not execute meaningfully.
The proposed patch series exposes the SEV injected secrets as virtual
files, which can later be used as decryption keys (as done in the kata
confidential containers use-case), or SSH private keys, or any other
possible implementation.
-Dov
On Tue, Jan 04, 2022 at 09:02:03AM +0200, Dov Murik wrote:
If the Guest Owner chooses to inject secrets via scp, it needs
to be sure it is scp-ing to the correct VM - the one that has SEV
enabled and was measured at launch.
Hmm, I'd expect that to be part of the attestation dance. I admit,
though, I have only listened about the whole attestation bla from the
sidelines so I'm unclear whether that's part of that protocol. I guess
Tom and Brijesh should have a better idea here.
One way to achieve that would be to inject the guest's SSH private key
Well, is that "one way" or *the way*?
using the proposed efi_secret mechanism. This way the Guest Owner is
sure it is talking to the correct guest and not to some other VM that
was started by the untrusted cloud provider (say, with SEV disabled so
the cloud provider can steal its memory content).
Because we would need *some* way of verifying the owner is talking
to the correct guest. And if so, this should be made part of the big
picture of SEV guest attestation. Or is this part of that attestation
dance?
I guess I'm wondering where in the big picture this fits into?
Indeed this proposed efi_secret module is in use for enabling SEV
confidential containers using Kata containers [1], but there's nothing
specific in the current patch series about containers. The patch series
just exposes the launch-injected SEV secrets to userspace as virtual files
(under securityfs).
[1] https://github.com/confidential-containers/attestation-agent/tree/main/src/kbc_modules/offline_sev_kbc
So one of the aspects for this is to use it in automated deployments.
It boils down to: the confidential guest needs to have access to a
secret which the untrusted host can't read, and which is essential for
the normal operation of the guest. This secret can be a decryption key,
an SSH private key, an API key to a Key Management system, etc. If a
malicious cloud provider tries to start that VM without a secret (or
with the wrong one), the actual workload that the guest is supposed to
run will not execute meaningfully.
The proposed patch series exposes the SEV injected secrets as virtual
files, which can later be used as decryption keys (as done in the kata
confidential containers use-case), or SSH private keys, or any other
possible implementation.
Right, and is this going to be the proper way to authenticate SEV guests
to their owners or is this just another technique for safely supplying
secrets into the guest?
I hope I'm making some sense here...
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
From: Dr. David Alan Gilbert <hidden> Date: 2022-01-05 11:43:35
* Borislav Petkov (bp@suse.de) wrote:
On Tue, Jan 04, 2022 at 09:02:03AM +0200, Dov Murik wrote:
quoted
If the Guest Owner chooses to inject secrets via scp, it needs
to be sure it is scp-ing to the correct VM - the one that has SEV
enabled and was measured at launch.
Hmm, I'd expect that to be part of the attestation dance. I admit,
though, I have only listened about the whole attestation bla from the
sidelines so I'm unclear whether that's part of that protocol. I guess
Tom and Brijesh should have a better idea here.
There's more than one type of dance; this partially varies
depending on the system (SEV/TDX etc) and also depends on how you depend
to boot your VM (separate kernel or VM disk). Also it's important to
note that when the dance happens varies - in SEV and SEV-ES this happens
before the guest executes any code.
So at the end of the dance, the guest owner hands over that secret - but
only then does the geust start booting; that secret has to go somewhere
to be used by something later.
For example, something might pull out that key and use it to decrypt a
disk that then has other secrets on it (e.g. your ssh key).
Dave
quoted
One way to achieve that would be to inject the guest's SSH private key
Well, is that "one way" or *the way*?
quoted
using the proposed efi_secret mechanism. This way the Guest Owner is
sure it is talking to the correct guest and not to some other VM that
was started by the untrusted cloud provider (say, with SEV disabled so
the cloud provider can steal its memory content).
Because we would need *some* way of verifying the owner is talking
to the correct guest. And if so, this should be made part of the big
picture of SEV guest attestation. Or is this part of that attestation
dance?
I guess I'm wondering where in the big picture this fits into?
quoted
Indeed this proposed efi_secret module is in use for enabling SEV
confidential containers using Kata containers [1], but there's nothing
specific in the current patch series about containers. The patch series
just exposes the launch-injected SEV secrets to userspace as virtual files
(under securityfs).
[1] https://github.com/confidential-containers/attestation-agent/tree/main/src/kbc_modules/offline_sev_kbc
So one of the aspects for this is to use it in automated deployments.
quoted
It boils down to: the confidential guest needs to have access to a
secret which the untrusted host can't read, and which is essential for
the normal operation of the guest. This secret can be a decryption key,
an SSH private key, an API key to a Key Management system, etc. If a
malicious cloud provider tries to start that VM without a secret (or
with the wrong one), the actual workload that the guest is supposed to
run will not execute meaningfully.
The proposed patch series exposes the SEV injected secrets as virtual
files, which can later be used as decryption keys (as done in the kata
confidential containers use-case), or SSH private keys, or any other
possible implementation.
Right, and is this going to be the proper way to authenticate SEV guests
to their owners or is this just another technique for safely supplying
secrets into the guest?
I hope I'm making some sense here...
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On Wed, Jan 05, 2022 at 11:43:25AM +0000, Dr. David Alan Gilbert wrote:
There's more than one type of dance;
So Brijesh and I talked about this a bit yesterday. There's all kinds of
dances...
this partially varies depending on the system (SEV/TDX etc)
By "SEV" I guess you mean pre-SNP because SNP attestation is reportedly
much better.
TDX I'm being told is not interested in something like that atm. I guess
they wanna do something different wrt attestation.
So what we're talking about here is pre-SNP attestation, AFAICT.
and also depends on how you depend to boot your VM (separate kernel
or VM disk). Also it's important to note that when the dance happens
varies - in SEV and SEV-ES this happens before the guest executes any
code. So at the end of the dance, the guest owner hands over that
secret - but only then does the geust start booting;
Right.
that secret has to go somewhere to be used by something later. For
example, something might pull out that key and use it to decrypt a
disk that then has other secrets on it (e.g. your ssh key).
That is the other example I heard about.
So, to sum up: this looks like part of a pre-SNP attestation flow, i.e.,
for SEV and SEV-ES guests.
Follow-up question: is this going to be used by other cloud vendors too?
Or am I gonna get another implementation of sharing secrets with a guest
which is just a little bit different but sender #2 can't use this one
because raisins?
Because that would not be good.
So, is this what cloud vendors using SEV/-ES guests would like to use
and what they all agree upon?
Thx.
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
From: Dr. David Alan Gilbert <hidden> Date: 2022-01-05 20:07:16
* Borislav Petkov (bp@suse.de) wrote:
On Wed, Jan 05, 2022 at 11:43:25AM +0000, Dr. David Alan Gilbert wrote:
quoted
There's more than one type of dance;
So Brijesh and I talked about this a bit yesterday. There's all kinds of
dances...
quoted
this partially varies depending on the system (SEV/TDX etc)
By "SEV" I guess you mean pre-SNP because SNP attestation is reportedly
much better.
TDX I'm being told is not interested in something like that atm. I guess
they wanna do something different wrt attestation.
I thought I saw something in their patch series where they also had a
secret that got passed down from EFI? As I remember they had it with an
ioctl and something; but it felt to me if it would be great if it was
shared.
So what we're talking about here is pre-SNP attestation, AFAICT.
quoted
and also depends on how you depend to boot your VM (separate kernel
or VM disk). Also it's important to note that when the dance happens
varies - in SEV and SEV-ES this happens before the guest executes any
code. So at the end of the dance, the guest owner hands over that
secret - but only then does the geust start booting;
Right.
quoted
that secret has to go somewhere to be used by something later. For
example, something might pull out that key and use it to decrypt a
disk that then has other secrets on it (e.g. your ssh key).
That is the other example I heard about.
So, to sum up: this looks like part of a pre-SNP attestation flow, i.e.,
for SEV and SEV-ES guests.
Yeh. SNP is a whole different question.
Follow-up question: is this going to be used by other cloud vendors too?
Or am I gonna get another implementation of sharing secrets with a guest
which is just a little bit different but sender #2 can't use this one
because raisins?
Because that would not be good.
So, is this what cloud vendors using SEV/-ES guests would like to use
and what they all agree upon?
I'd love to hear from those other cloud vendors; I've not been able to
find any detail on how their SEV(-ES) systems actually work.
However, this aims to be just a comms mechanism to pass that secret;
so it's pretty low down in the stack and is there for them to use -
hopefully it's general enough.
(An interesting question is what exactly gets passed in this key and
what it means).
All the contentious stuff I've seen seems to be further up the stack - like
who does the attestation and where they get the secrets and how they
know what a valid measurement looks like.
Dave
Thx.
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
I'd love to hear from those other cloud vendors; I've not been able to
find any detail on how their SEV(-ES) systems actually work.
Same here.
However, this aims to be just a comms mechanism to pass that secret;
so it's pretty low down in the stack and is there for them to use -
hopefully it's general enough.
Exactly!
(An interesting question is what exactly gets passed in this key and
what it means).
All the contentious stuff I've seen seems to be further up the stack - like
who does the attestation and where they get the secrets and how they
know what a valid measurement looks like.
It would be much much better if all the parties involved would sit down
and decide on a common scheme so that implementation can be shared but
getting everybody to agree is likely hard...
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
I'd love to hear from those other cloud vendors; I've not been able to
find any detail on how their SEV(-ES) systems actually work.
Same here.
quoted
However, this aims to be just a comms mechanism to pass that secret;
so it's pretty low down in the stack and is there for them to use -
hopefully it's general enough.
Exactly!
quoted
(An interesting question is what exactly gets passed in this key and
what it means).
All the contentious stuff I've seen seems to be further up the stack - like
who does the attestation and where they get the secrets and how they
know what a valid measurement looks like.
It would be much much better if all the parties involved would sit down
and decide on a common scheme so that implementation can be shared but
getting everybody to agree is likely hard...
I saw a request for other cloud provider input here. A little
background for our SEV VMs in GCE we rely on our vTPM for attestation,
we do this because of SEV security properties quoting from AMD being
to protect guests from a benign but vulnerable hypervisor. So a
benign/compliant hypervisor's vTPM wouldn't lie to the guest. So we
added a few bits in the PCRs to allow users to see their SEV status in
vTPM quotes.
It would be very interesting to offer an attestation solution that
doesn't rely on our virtual TPM. But after reading through this cover
letter and the linked OVMF patches I am confused what's the high level
flow you are working towards? Are you loading in some OVMF using
LAUNCH_UPDATE_DATA, getting the measurement with LAUNCH_MEASURE, then
sending that to the customer who can then craft a "secret" (maybe say
SSH key) for injection with LAUNCH_SECRET? Thats sounds good but there
are a lot details left unattested there, how do you know you will boot
from the image loaded with the PSP into a known state? Do you have
some documentation I could read through to try and understand a little
more and apologies if I missed it.
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
I'd love to hear from those other cloud vendors; I've not been able to
find any detail on how their SEV(-ES) systems actually work.
Same here.
quoted
However, this aims to be just a comms mechanism to pass that secret;
so it's pretty low down in the stack and is there for them to use -
hopefully it's general enough.
Exactly!
quoted
(An interesting question is what exactly gets passed in this key and
what it means).
All the contentious stuff I've seen seems to be further up the stack - like
who does the attestation and where they get the secrets and how they
know what a valid measurement looks like.
It would be much much better if all the parties involved would sit down
and decide on a common scheme so that implementation can be shared but
getting everybody to agree is likely hard...
I saw a request for other cloud provider input here. A little
background for our SEV VMs in GCE we rely on our vTPM for attestation,
we do this because of SEV security properties quoting from AMD being
to protect guests from a benign but vulnerable hypervisor. So a
benign/compliant hypervisor's vTPM wouldn't lie to the guest. So we
added a few bits in the PCRs to allow users to see their SEV status in
vTPM quotes.
Thanks Peter for explaining the GCE approach. If I understand correctly,
if the hypervisor is malicious, it could lie to the vTPM and set those
"few bits" so it'll look like the VM is running with SEV enabled (whereas
in fact it is running without memory encryption). But that's outside the
scope, right?
It would be very interesting to offer an attestation solution that
doesn't rely on our virtual TPM. But after reading through this cover
letter and the linked OVMF patches I am confused what's the high level
flow you are working towards? Are you loading in some OVMF using
LAUNCH_UPDATE_DATA, getting the measurement with LAUNCH_MEASURE, then
sending that to the customer who can then craft a "secret" (maybe say
SSH key) for injection with LAUNCH_SECRET? Thats sounds good but there
are a lot details left unattested there, how do you know you will boot
from the image loaded with the PSP into a known state? Do you have
some documentation I could read through to try and understand a little
more and apologies if I missed it.
We rely on the OvmfPkg/AmdSev build of OVMF, which is a stripped down
firmware that can boot only in one of two ways:
a. direct boot to kernel/initrd/cmdline whose hashes are included in
the LAUNCH_MEASURE data (see [1], [2], [3]).
b. boot to embedded grub (in OVMF) which decrypts an encrypted boot drive
using a secret from LAUNCH_SECRET (see [4] and [5]).
For the current series (efi_secret kernel module), method (a) is the relevant
one. The Cloud Provider boots a guest VM with OVMF, and -kernel/-initrd/-append. The
content of OVMF and the hashes of kernel/initrd/cmdline are measured in LAUNCH_MEASURE
and sent to the Guest Owner (=Customer). If they match, the Guest Owner should perform
a LAUNCH_SECRET and inject the secret to a designated SEV launch secrets page.
Then the guest starts running; when the kernel starts the EFI driver saves the address
of this page (patch 1), and later exposes the secrets in this page as files in
securityfs (patch 3). The secrets can be used by the guest workload in whatever way
it needs (examples discussed above: ssh private key; API key to obtain secrets;
decryption key for some encrypted files; ...).
Any attempt of a malicious cloud provider to modify OVMF, kernel, initrd, or cmdline
will cause the SEV measurement to be wrong.
Note again that the proposed kernel patch series has nothing to do with the measurement
sequence -- it assumes the secrets page is already populated, and exposes it
to userspace as files.
Hope this explains our approach.
[1] https://www.youtube.com/watch?v=jzP8RlTRErk
[2] https://lore.kernel.org/qemu-devel/20210930054915.13252-1-dovmurik@linux.ibm.com/
[3] https://lore.kernel.org/qemu-devel/20211111100048.3299424-1-dovmurik@linux.ibm.com/
[4] https://www.youtube.com/watch?v=rCsIxzM6C_I
[5] https://blog.hansenpartnership.com/deploying-encrypted-images-for-confidential-computing/
-Dov
I'd love to hear from those other cloud vendors; I've not been able to
find any detail on how their SEV(-ES) systems actually work.
Same here.
quoted
However, this aims to be just a comms mechanism to pass that secret;
so it's pretty low down in the stack and is there for them to use -
hopefully it's general enough.
Exactly!
quoted
(An interesting question is what exactly gets passed in this key and
what it means).
All the contentious stuff I've seen seems to be further up the stack - like
who does the attestation and where they get the secrets and how they
know what a valid measurement looks like.
It would be much much better if all the parties involved would sit down
and decide on a common scheme so that implementation can be shared but
getting everybody to agree is likely hard...
I saw a request for other cloud provider input here.
Thanks for the reply!
A little
background for our SEV VMs in GCE we rely on our vTPM for attestation,
we do this because of SEV security properties quoting from AMD being
to protect guests from a benign but vulnerable hypervisor. So a
benign/compliant hypervisor's vTPM wouldn't lie to the guest. So we
added a few bits in the PCRs to allow users to see their SEV status in
vTPM quotes.
OK, so we're trying to protect from a malicious hypervisor - we don't
trust anything on the host (other than the CPU, and it's got to be
signing the attestation); we don't think there's a way to do that with
a vTPM on plain SEV/SEV-ES
It would be very interesting to offer an attestation solution that
doesn't rely on our virtual TPM. But after reading through this cover
letter and the linked OVMF patches I am confused what's the high level
flow you are working towards? Are you loading in some OVMF using
LAUNCH_UPDATE_DATA, getting the measurement with LAUNCH_MEASURE, then
sending that to the customer who can then craft a "secret" (maybe say
SSH key) for injection with LAUNCH_SECRET? Thats sounds good but there
are a lot details left unattested there, how do you know you will boot
from the image loaded with the PSP into a known state? Do you have
some documentation I could read through to try and understand a little
more and apologies if I missed it.
I'll defer to Dov's reply on that.
Dave
quoted
--
Regards/Gruss,
Boris.
SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK