linux-kernel - Re: [RFC 0/2] ima: evm: Add kernel cmdline options to disable IMA/EVM

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Message-ID: <746B14AA-7C89-451F-BE8D-3D2C485AA9E9@fb.com>
Date: Wed, 18 Dec 2024 16:48:46 +0000
From: Song Liu <songliubraving@...a.com>
To: Casey Schaufler <casey@...aufler-ca.com>
CC: Song Liu <songliubraving@...a.com>,
        "roberto.sassu@...wei.com"
	<roberto.sassu@...wei.com>,
        Paul Moore <paul@...l-moore.com>, Song Liu
	<song@...nel.org>,
        "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>,
        "linux-integrity@...r.kernel.org"
	<linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org"
	<linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "dmitry.kasatkin@...il.com"
	<dmitry.kasatkin@...il.com>,
        "eric.snowberg@...cle.com"
	<eric.snowberg@...cle.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        Kernel Team <kernel-team@...a.com>,
        "brauner@...nel.org" <brauner@...nel.org>,
        "jack@...e.cz" <jack@...e.cz>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: [RFC 0/2] ima: evm: Add kernel cmdline options to disable IMA/EVM



> On Dec 18, 2024, at 8:42 AM, Casey Schaufler <casey@...aufler-ca.com> wrote:
> 
> On 12/17/2024 10:41 PM, Song Liu wrote:
>>> On Dec 17, 2024, at 3:33 PM, Song Liu <songliubraving@...a.com> wrote:
>> [...]
>> 
>>>>> +
>>>>>                              found = true;
>>>>>                      }
>>>>>              }
>>>>> @@ -386,7 +389,7 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
>>>>> 
>>>>>      /* LSM_ORDER_LAST is always last. */
>>>>>      for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
>>>>> -               if (lsm->order == LSM_ORDER_LAST)
>>>>> +               if (lsm->order == LSM_ORDER_LAST && is_enabled(lsm))
>>>>>                      append_ordered_lsm(lsm, "   last");
>>> Before this change, lsm with order==LSM_ORDER_LAST is always considered
>>> enabled, which is a bug (if I understand you and Casey correctly).
>> According to commit 42994ee3cd7298b27698daa6848ed7168e72d056, LSMs with 
>> order LSM_ORDER_LAST is expected to be always enabled:
>> 
>> "Similarly to LSM_ORDER_FIRST, LSMs with LSM_ORDER_LAST are always enabled
>> and put at the end of the LSM list, if selected in the kernel
>> configuration. "
>> 
>> Roberto, it feels weird to have two "last and always on" LSMs (ima and evm)
>> I guess this is not the expected behavior? At least, it appears to be a
>> surprise for Paul and Casey.
> 
> I can't speak for Paul, but having multiple "first" and "last" entries
> comes as no surprise to me. We should probably have used LSM_ORDER_EARLY
> and LSM_ORDER_LATE instead of LSM_ORDER_FIRST and LSM_ORDER_LAST. As for
> "always on", I recall that being an artifact of compatibility for the
> security= boot option.

Yes, _LATE makes more sense than _LAST. _LAST is a bit weird, but not
surprising. 

By "surprise to you and Paul", I meant the "always on" part. It appears
to me that both you and Paul believed that ima and evm are only enabled 
with proper lsm= cmdline. Or maybe I totally misunderstood your
comments?

Thanks,
Song