[PATCH v7 0/4] use more system keyrings to verify arm64 and s390 kexec kernel image signature

[Coiby Xu <coxu@redhat.com>]

Currently, a problem faced by arm64 is if a kernel image is signed by a
MOK key, loading it via the kexec_file_load() system call would be
rejected with the error "Lockdown: kexec: kexec of unsigned images is
restricted; see man kernel_lockdown.7". This happens because arm64 uses
only the primary keyring i.e. the .builtin_trusted_keys keyring that
contains only kernel built-in keys to verify the kexec kernel image. MOK
keys are loaded into the .platform keyring or/and .machine keyring. The
.machine keyring is linked to the secondary keyring i.e.
.secondary_trusted_keys keyring when the end-user chooses to trust MOK
keys. The platform keyring is exclusively used for kexec kernel image
verification and .secondary_trusted_keys together with
.builtin_trusted_keys are the system trusted keyrings. So obviously
there is no reason to not use .secondary_trusted_keys or .platform
keyring for kernel image signature verification. 

Similarly, s390 only uses platform keyring for kernel image signature
verification and built-in keys and secondary keyring are not used.

This patch set allows arm64 and s390 to use more system keyrings
including the .secondary_trusted_keys and .platform keyring to verify
kexec kernel image signature as x86 does.

The 3rd arm64 patch depends on the first two patches. The 4th s390 patch
can be applied independently.

v7:
 - drop the Fixes tag for the 2nd patch and add patch prerequisites
   [Baoquan]
 - improve cover letter

v6:
 - integrate the first three patches of "[PATCH 0/4] Unifrom keyring
   support across architectures and functions" from Michal [1]
 - improve commit message [Baoquan, Michal]
 - directly assign kexec_kernel_verify_pe_sig to
   kexec_file_ops->verify_sig [Michal]

v5:
 - improve commit message [Baoquan]

v4:
 - fix commit reference format issue and other checkpatch.pl warnings [Baoquan]

v3:
 - s/arch_kexec_kernel_verify_pe_sig/kexec_kernel_verify_pe_sig [Eric]
 - clean up arch_kexec_kernel_verify_sig [Eric]

v2:
 - only x86_64 and arm64 need to enable PE file signature check [Dave]

[1] https://lore.kernel.org/lkml/cover.1644953683.git.msuchanek at suse.de/

Coiby Xu (3):
  kexec: clean up arch_kexec_kernel_verify_sig
  kexec, KEYS: make the code in bzImage64_verify_sig generic
  arm64: kexec_file: use more system keyrings to verify kernel image
    signature

Michal Suchanek (1):
  kexec, KEYS, s390: Make use of built-in and secondary keyring for
    signature verification

 arch/arm64/kernel/kexec_image.c       | 11 +-----
 arch/s390/kernel/machine_kexec_file.c | 18 +++++++---
 arch/x86/kernel/kexec-bzimage64.c     | 20 +----------
 include/linux/kexec.h                 |  7 ++--
 kernel/kexec_file.c                   | 51 ++++++++++++++++-----------
 5 files changed, 50 insertions(+), 57 deletions(-)

-- 
2.35.3