543ce63b66
The lockdown LSM is primarily used in conjunction with UEFI Secure Boot.
This LSM may also be used on machines without UEFI. It can also be
enabled when UEFI Secure Boot is disabled. One of lockdown's features
is to prevent kexec from loading untrusted kernels. Lockdown can be
enabled through a bootparam or after the kernel has booted through
securityfs.
If IMA appraisal is used with the "ima_appraise=log" boot param,
lockdown can be defeated with kexec on any machine when Secure Boot is
disabled or unavailable. IMA prevents setting "ima_appraise=log" from
the boot param when Secure Boot is enabled, but this does not cover
cases where lockdown is used without Secure Boot.
To defeat lockdown, boot without Secure Boot and add ima_appraise=log to
the kernel command line; then:
$ echo "integrity" > /sys/kernel/security/lockdown
$ echo "appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig" > \
/sys/kernel/security/ima/policy
$ kexec -ls unsigned-kernel
Add a call to verify ima appraisal is set to "enforce" whenever lockdown
is enabled. This fixes CVE-2022-21505.
Cc: stable@vger.kernel.org
Fixes:
|
||
|---|---|---|
| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.