From: Eric Snowberg eric.snowberg@oracle.com
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.
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 --- security/integrity/ima/ima_policy.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -1805,6 +1805,10 @@ bool ima_appraise_signature(enum kernel_ if (id >= READING_MAX_ID) return false;
+ if (id == READING_KEXEC_IMAGE && !(ima_appraise & IMA_APPRAISE_ENFORCE) + && security_locked_down(LOCKDOWN_KEXEC)) + return false; + func = read_idmap[id] ?: FILE_CHECK;
rcu_read_lock();