This patch set contains v13 the consolidated version of the patch
sets for secure boot using appended signatures on powerpc,
rebased on top of git HEAD.
The v12 series is at
https://lists.gnu.org/archive/html/grub-devel/2025-09/msg00197.html
Changes since v12:
- Daniel Kiper review comments addressed:
- v13 patch 11: changed the function name from grub_pks_tmp_free to
grub_pks_free_data, corrected the typo error.
- v13 patch 12 - 20: Addressed all comments.
- v13: Removed the patch 16 and patch 17 from v12.
Linux on Power LPAR secure boot ensures the integrity of the Linux boot
stack. The hypervisor and partition firmware are part of the core root
of
trust. The partition firmware verifies the signature on the GRUB image
before handing control to GRUB. Similarly, GRUB verifies the signature
on
the kernel image before booting the OS. This ensures that every image
running at the boot time is verified and trusted. UEFI platforms relies
on PECOFF based signature scheme. Since Power is not a UEFI platform,
an
alternative mechanism is needed. Power already uses appended signatures
on the Linux Kernel, and is now extended to sign the grub as well.
Linux on Power also allows multiple signers, and if any one of the
signature passes, then the image passes the validation. Appended
signature
scheme uses CMS structure to contain signatures. On Power, the multiple
signature support relies on the multiple signers features already
supported
by CMS standards. It does require that all the signers should sign at
the
same time and are not allowed to add or remove the signatures randomly.
By default, Linux LPAR secure boot uses static key management[1]. This
means
that each image embeds the keys it needs to verify the image it loads.
For example, the keys used to verify the GRUB image are built into the
firmware image. Similarly, the keys used for verifying the kernel image
are built into the GRUB image. These are pre-defined keys and they
cannot
be modified at runtime. The drawback of this approach is that key
rotations
results in both firmware and OS updates. This is where dynamic key
management is useful.
An admin can switch from static keys to dynamic keys by coordinating
with
Hardware Management Console(HMC) admin and enabling the required flags
for the given LPAR.
The dynamic key management relies on the Platform KeyStore(PKS)[2]
storage
allocation for each LPAR with individually managed access controls to
store sensitive information securely. Once switched to dynamic keys,
HMC
advertises this flag to the PowerVM, which then initializes the PKS
with the default secvars. It also creates a variable SB_VERSION that
represents the secure boot key management mode. The default secvars are
used by Partition firmware, grub and the linux kernel to reads keys for
verification. These secvars can be managed by user interface exposed
via
linux kernel. The linux kernel already supports this interface and
it is available in the upstream kernel.
This patchset adds the appended signature support both for signing and
verification and the key management to the grub component. The whole
patchset can be split into following four main parts:
The series has following four main parts:
1.) Sign grub.elf with an appended signature. (Patches 1, 18, 19)
These patches provide some infrastructure and documentation for
signing grub's core.elf with a Linux-kernel-module style appended
signature.
An appended signature is a 'dumb' signature over the contents of a
file. (It is distinct from schemes like Authenticode that are aware of
the structure of the file and only sign certain parts.) The signature
is wrapped in a PKCS#7 message, and is appended to the signed file
along with some metadata and a magic string. The signatures are
validated against a public key which is usually provided as an x509
certificate.
Because some platforms, such as powerpc-ieee1275, may load grub from a
raw disk partition rather than a filesystem, we extend grub-install to
add an ELF note that allows us to specify the size and location of the
signature.
2.) Enable lockdown if secure boot is enabled (Patch 9)
Read secure boot mode from 'ibm,secure-boot' property and
If the 'ibm,secure-boot' property of the root node is 2,
enter lockdown. Else it is considered as disabled.
There are three secure boot modes. They are
0 - disabled
No signature verification is performed. This is the default.
1 - audit
Signature verification is performed and if signature verification
fails, post the errors and allow the boot to continue.
2 - enforce
Lockdown the GRUB. Signature verification is performed and
If signature verification fails, post the errors and stop the
boot.
Now, only support disabled and enforce.
3.) Enable appended signature verification using builtin keys (Patches
2 - 8
and 10).
Part of a secure boot chain is allowing grub to verify the boot
kernel. For UEFI platforms, this is usually delegated to the
shim. However, for platforms that do not implement UEFI, an
alternative scheme is required.
This part teaches grub how to verify Linux kernel-style appended
signatures. Kernels on powerpc are already signed with this scheme and
can be verified by IMA for kexec.
As PKCS#7 messages and x509 certificates are both based on ASN.1, we
import libtasn1 to parse them. Because ASN.1 isn't self-documenting,
we import from GNUTLS the information we need to navigate their
structure.
This section is composed of the following patches:
- patches 2 and 3 are small refactorings.
- patch 4 allows x509 certificates to be built in to the grub core
in much the same way as PGP keys.
- patch 5 brings in the code from GNUTLS that allows us to parse
PKCS#7 and x509 with libtasn1.
- patch 6, 7 and 8 is our ASN1 node, PKCS#7 and x509 parser. They're
minimal
and fairly strict parsers that extract only the bits we need to
verify the
signatures.
- patch 10 is the guts of the appended signature verifier.
4.) Enable accessing keys dynamically from Platform KeyStore (Patch 11
- 16)
This part teaches grub how to read db and dbx variables from platform
keystore
using client interface call then load keys from those two variable, and
use it
to verify Linux kernel.
This section is composed of the following patches:
- patch 11 is an exposes an interface in ieee1275 for reading secure
boot
variable db and dbx from Platform Keystore. Read secure boot
variables
such as db and dbx from PKS and extract certificates from ESL.
- patch 12 is introducing key management environment variable.
- patch 13 is create the db and dbx lists from PKS.
- patch 14 is verify the kernel using db and dbx lists
- patch 15 is GRUB commands to manage the certificates
- patch 16 adds GRUB commands to access db and dbx.
5.) patch 17 adds unit test and 20 adds GRUB commands and an appended
signatures
documentation.
Thanks to Daniel Kiper for providing review comments.
I've pushed this all to
https://github.com/SudhakarKuppusamy1/grub/tree/appendedsig-2.13
[1]https://www.ibm.com/docs/en/linux-on-systems?topic=servers-guest-secure-boot-static-keys
[2]https://community.ibm.com/community/user/power/blogs/chris-engel1/2020/11/20/powervm-introduces-the-platform-keystore
Daniel Axtens (2):
crypto: Move storage for grub_crypto_pk_* to crypto.c
docs/grub: Document signing GRUB under UEFI
Sudhakar Kuppusamy (18):
powerpc-ieee1275: Add support for signing GRUB with an appended
signature
pgp: Rename OBJ_TYPE_PUBKEY to OBJ_TYPE_GPG_PUBKEY
grub-install: Support embedding x509 certificates
appended signatures: Import GNUTLS's ASN.1 description files
appended signatures: Parse ASN1 node
appended signatures: Parse PKCS#7 signed data
appended signatures: Parse X.509 certificates
powerpc_ieee1275: Enter lockdown based on /ibm,secure-boot
appended signatures: Support verifying appended signatures
powerpc_ieee1275: Read the db and dbx secure boot variables
appended signatures: Introducing key management environment variable
appended signatures: Create db and dbx lists
appended signatures: Using db and dbx lists for signature
verification
appended signatures: GRUB commands to manage the certificates
appended signatures: GRUB commands to manage the hashes
appended signatures: Verification tests
docs/grub: Document signing GRUB with an appended signature
docs/grub: Document appended signature
docs/grub.texi | 475 ++++-
grub-core/Makefile.am | 2 +
grub-core/Makefile.core.def | 26 +
grub-core/commands/appendedsig/appendedsig.c | 1723 +++++++++++++++++
grub-core/commands/appendedsig/appendedsig.h | 133 ++
grub-core/commands/appendedsig/asn1util.c | 99 +
.../commands/appendedsig/gnutls_asn1_tab.c | 148 ++
grub-core/commands/appendedsig/pkcs7.c | 452 +++++
.../commands/appendedsig/pkix_asn1_tab.c | 485 +++++
grub-core/commands/appendedsig/x509.c | 970 ++++++++++
grub-core/commands/pgp.c | 6 +-
grub-core/kern/ieee1275/ieee1275.c | 1 -
grub-core/kern/ieee1275/init.c | 58 +
grub-core/kern/powerpc/ieee1275/ieee1275.c | 137 ++
.../kern/powerpc/ieee1275/platform_keystore.c | 344 ++++
grub-core/lib/crypto.c | 4 +
grub-core/tests/appended_signature_test.c | 348 ++++
grub-core/tests/appended_signatures.h | 975 ++++++++++
grub-core/tests/lib/functional_test.c | 1 +
include/grub/crypto.h | 1 +
include/grub/efi/pks.h | 112 ++
include/grub/err.h | 3 +-
include/grub/file.h | 4 +
include/grub/ieee1275/ieee1275.h | 3 +
include/grub/kernel.h | 3 +-
include/grub/lockdown.h | 3 +-
include/grub/powerpc/ieee1275/ieee1275.h | 18 +
.../grub/powerpc/ieee1275/platform_keystore.h | 122 ++
include/grub/types.h | 4 +
include/grub/util/install.h | 10 +-
include/grub/util/mkimage.h | 4 +-
util/grub-install-common.c | 36 +-
util/grub-mkimage.c | 26 +-
util/grub-mkimagexx.c | 40 +-
util/mkimage.c | 50 +-
35 files changed, 6782 insertions(+), 44 deletions(-)
create mode 100644 grub-core/commands/appendedsig/appendedsig.c
create mode 100644 grub-core/commands/appendedsig/appendedsig.h
create mode 100644 grub-core/commands/appendedsig/asn1util.c
create mode 100644 grub-core/commands/appendedsig/gnutls_asn1_tab.c
create mode 100644 grub-core/commands/appendedsig/pkcs7.c
create mode 100644 grub-core/commands/appendedsig/pkix_asn1_tab.c
create mode 100644 grub-core/commands/appendedsig/x509.c
create mode 100644 grub-core/kern/powerpc/ieee1275/ieee1275.c
create mode 100644 grub-core/kern/powerpc/ieee1275/platform_keystore.c
create mode 100644 grub-core/tests/appended_signature_test.c
create mode 100644 grub-core/tests/appended_signatures.h
create mode 100644 include/grub/efi/pks.h
create mode 100644 include/grub/powerpc/ieee1275/platform_keystore.h
