> On Feb 7, 2020, at 10:40 AM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote:
>
> On Fri, 2020-02-07 at 09:57 -0700, Eric Snowberg wrote:
>>> On Feb 7, 2020, at 7:51 AM, Mimi Zohar <zohar@xxxxxxxxxxxxx> wrote:
>>>
>>> On Thu, 2020-02-06 at 14:40 -0700, Eric Snowberg wrote:
>>>
>>> <snip>
>>>
>>>> Currently the upstream code will fail if the module is uncompressed.
>>>> If you compress the same module it will load with the current
>>>> upstream code.
>>>>
>>>>> Lastly, there is nothing in these patches that indicate that the
>>>> kernel modules being compressed/uncompressed is related to the
>>>> signature verification.
>>>>>
>>>>
>>>> Basically if you have the following setup:
>>>>
>>>> Kernel built with CONFIG_IMA_ARCH_POLICY or kernel booted with
>>>> module.sig_enforce=1 along with the following ima policy:
>>>>
>>>> appraise func=MODULE_CHECK appraise_type=imasig|modsig
>>>
>>> Enabling CONFIG_IMA_ARCH_POLICY or module.sig_enforce=1 behave totally
>>> differently. CONFIG_IMA_ARCH_POLICY coordinates between the IMA
>>> signature verification and the original module_sig_check()
>>> verification. Either one signature verification method is enabled or
>>> the other, but not both.
>>>
>>> The existing IMA x86 arch policy has not been updated to support
>>> appended signatures.
>>
>> That is not what I’m seeing. Appended signatures mostly work. They just
>> don’t work thru the finit_module system call.
>>
>>> To understand what is happening, we need to analyze each scenario
>>> separately.
>>>
>>> - If CONFIG_MODULE_SIG is configured or enabled on the boot command
>>> line ("module.sig_enforce = 1"), then the IMA arch x86 policy WILL NOT
>>> require an IMA signature.
>>
>> All tests below are without my change
>> x86 booted with module.sig_enforce=1
>>
>> empty ima policy
>
> Sure, in this example the IMA arch x86 policy is not configured and
> there is no custom IMA policy - no IMA.
>
>> $ cat /sys/kernel/security/ima/policy
>
> On a real system, you would want to require a signed IMA policy.
>
>> $ insmod ./foo.ko.xz <— loads ok
>> $ rmmod foo
>> $ unxz ./foo.ko.xz
>> $ insmod ./foo.ko <— loads ok
>> $ rmmod foo
>>
>> add in module appraisal
>
> Sure, the current system
>
>> $ echo "appraise func=MODULE_CHECK appraise_type=imasig|modsig" >
>> /sys/kernel/security/ima/policy
>>
>> $ insmod ./foo.ko.xz <— loads ok
>> $ rmmod foo
>
> Sure, CONFIG_MODULE_SIG is configured or enabled on the boot command
> line ("module.sig_enforce = 1"). IMA won't prevent the init_module()
> syscall.
>
>>
>> $ insmod ./foo.ko
>> insmod: ERROR: could not insert module ./foo.ko: Permission denied
>>
>> last entry from audit log:
>> type=INTEGRITY_DATA msg=audit(1581089373.076:83): pid=2874 uid=0
>> auid=0 ses=1 subj=unconfined_u:unconfined_r:unconfined_t:s0-
>> s0:c0.c1023 op=appraise_data cause=invalid-signature comm="insmod"
>> name="/root/keys/modules/foo.ko" dev="dm-0" ino=10918365
>> res=0^]UID="root" AUID=“root"
>>
>> This is because modsig_verify() will be called from within
>> ima_appraise_measurement(),
>> since try_modsig is true. Then modsig_verify() will return
>> INTEGRITY_FAIL.
>
> Why is it an "invalid signature"? For that you need to look at the
> kernel messages. Most likely it can't find the public key on the .ima
> keyring to verify the signature.
It is invalid because the module has not been ima signed.
