linux-kernel - Re: [PATCH v5 1/2] IMA: Define workqueue for early boot "key" measurements

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Message-ID: <503845c9-beeb-b520-ec3f-af5fa7d2b91f@linux.microsoft.com>
Date:   Thu, 19 Dec 2019 08:55:38 -0800
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>,
        James.Bottomley@...senPartnership.com,
        linux-integrity@...r.kernel.org
Cc:     eric.snowberg@...cle.com, dhowells@...hat.com,
        mathew.j.martineau@...ux.intel.com, matthewgarrett@...gle.com,
        sashal@...nel.org, jamorris@...ux.microsoft.com,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH v5 1/2] IMA: Define workqueue for early boot "key"
 measurements

On 12/19/19 5:11 AM, Mimi Zohar wrote:

> 
> Getting rid of the temporary list is definitely a big improvement.  As
> James suggested, using test_and_set_bit() and test_bit() would improve
> this code even more.  I think, James correct me if I'm wrong, you
> would be able to get rid of both the mutex and "process".
> 
> Mimi

I am not sure if the mutex can be removed.

In ima_queue_key() we need to test the flag and add the key to the list 
as an atomic operation:

  if (!test_bit())
     insert_key_to_list

Suppose the if condition is true, but before we could insert the key to 
the list, ima_process_queued_keys() runs and processes queued keys we'll 
add the key to the list and never process it.

Is there an API in the kernel to test and add an entry to a list 
atomically?

thanks,
  -lakshmi