On Sat, 2025-10-18 at 07:19 +0800, Coiby Xu wrote: > > > > 2. Instead of defining an additional process_measurement() argument to > > > > identify > > > > compressed kernel modules, to simplify the code it might be possible to > > > > define a > > > > new "func" named COMPRESSED_MODULE_CHECK. > > > > > > > > + [READING_COMPRESSED_MODULE] = MODULE_CHECK, -> > > > > COMPRESSED_MODULE_CHECK > > > > > > I also thought about this approach. But IMA rule maps kernel module > > > loading to MODULE_CHECK. If we define a new rule and ask users to use > > > this new rule, ima_policy=secure_boot still won't work. > > > > I don't have a problem with extending the "secure-boot" policy to support > > uncompressed kernel modules appended signatures, based on whether > > CONFIG_MODULE_SIG is enabled. The new rule would be in addition to the > > existing > > MODULE_CHECK rule. > > I assume once the new rule get added, we can't remove it for userspace > backward compatibility, right? And with CPIO xattr supported, it seems > there is no need to keep this rule. So if this concern is valid, do you > think we shall switch to another approach i.e. to make IMA support > verifying decompressed module and then make "secure-boot" to allow > appended module signature?
Yes, once the rule is added, it wouldn't be removed. As for "to make IMA support verifying decompressed module", yes that might be a better solution, than relying on "sig_enforce" being enabled. IMA already supports verifying the appended signatures. A new IMA specific or LSM hook would need to be defined after module_decompress(). Remember based on policy, IMA supports: 1. verifying the signature stored in security.ima xattr 2. verifying the appended signature (not for compressed kernel modules) 3. verifying both the xattr and appended signatures 4. none To prevent 3 - verifying both types of signatures, the IMA arch specific policy rule only adds the "appraise func=MODULE_CHECK ..." rule if CONFIG_MODULE_SIG is NOT enabled. Calling set_module_sig_enforced() from ima_appraise_measurement() to set sig_enforce could inadvertently result in requiring both the xattr and the appended signature kernel module verification. To prevent this from happening, "sig_enforce" should not be set, only verified in ima_appraise_measurement(). > > Another thought is to make CPIO support xattr. Today I realize that > ima_policy=secure_boot can also cause failure of loading kdump kernel. > So the issue this patch tries to resolves has much less impact than I > thought. Maybe we can wait until CPIO xattr support is ready? I'll help > review and test Roberto's patches if this is the best way forward. I'm not sure of the status of the CPIO patch set. Roberto? Mimi
