tree f64374c37e713aba7e583ce4e8d5dab470a5d2a4
parent 8339df9b3f28bad265f645cad9d96530c90d8675
author Eric Snowberg <eric.snowberg@oracle.com> 1658335227 -0400
committer Meena Shanmugam <meenashanmugam@google.com> 1659461769 +0000

lockdown: Fix kexec lockdown bypass with ima policy

commit 543ce63b664e2c2f9533d089a4664b559c3e6b5b upstream.

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.

BUG=b/239715669
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2022-21505 in the Linux kernel.

Cc: stable@vger.kernel.org
Fixes: 29d3c1c8dfe7 ("kexec: Allow kexec_file() with appropriate IMA policy when locked down")
Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: John Haxby <john.haxby@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

cos-patch: security-moderate
Change-Id: Id19d2e018ff9b5f6690a3c76aacb072c61931d07
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/35511
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>