Re: [PATCH 15/15] xsm: add a default policy to .init.data

From: Daniel De Graaf <dgdegra@tycho.nsa.gov>
To: Andrew Cooper <andrew.cooper3@citrix.com>, xen-devel@lists.xen.org
Subject: Re: [PATCH 15/15] xsm: add a default policy to .init.data
Date: Thu, 9 Jun 2016 12:58:17 -0400	[thread overview]
Message-ID: <3adb76f3-ea0c-798f-6eb7-5f25976a0626@tycho.nsa.gov> (raw)
In-Reply-To: <57598BA5.2070804@citrix.com>

On 06/09/2016 11:30 AM, Andrew Cooper wrote:
> On 09/06/16 15:47, Daniel De Graaf wrote:
>> diff --git a/xen/xsm/xsm_core.c b/xen/xsm/xsm_core.c
>> index 4a264c2..6ffccb2 100644
>> --- a/xen/xsm/xsm_core.c
>> +++ b/xen/xsm/xsm_core.c
>> @@ -36,6 +36,17 @@ static inline int verify(struct xsm_operations *ops)
>>      return 0;
>>  }
>>
>> +extern char __xsm_init_policy_start[], __xsm_init_policy_end[];
>> +
>> +static void __init xsm_policy_init(void)
>> +{
>> +    if ( policy_size == 0 && __xsm_init_policy_end != __xsm_init_policy_start )
>> +    {
>> +        policy_buffer = __xsm_init_policy_start;
>
> I think this might cause a problem for ARM.
>
> xsm_dt_init(void) does
>
> ret = xsm_core_init();
> xfree(policy_buffer);
>
> which might now try freeing a piece of initdata.  Even going back to c/s
> a8f2fb51c19 which introduced this code, I can't spot its justification.

The buffer is allocated and populated in xsm_dt_policy_init.

> It also looks like the entire policy buffer can be const, at which point
> it can be linked slightly higher in .init.data with the other
> logically-const data.

Sure, although this will require quite a bit of const propagation down into
the FLASK security server (or casting it away).

-- 
Daniel De Graaf
National Security Agency

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