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

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Message-ID: <518fdb73-8daf-4181-a8e6-528e4824d955@schaufler-ca.com>
Date: Wed, 18 Dec 2024 08:42:39 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Song Liu <songliubraving@...a.com>,
 "roberto.sassu@...wei.com" <roberto.sassu@...wei.com>
Cc: 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>,
 Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC 0/2] ima: evm: Add kernel cmdline options to disable IMA/EVM

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.

> I will send patch that allow enable/disable ima and evm with lsm= cmdline.
> We can further discuss the topic with the patch. 
>
> Thanks,
> Song
>
>