From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
Subject: Re: [PATCH V2] x86,
 amd_ucode: Verify max allowed patch size before apply
Date: Wed, 30 Apr 2014 15:13:44 -0500
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To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Thomas.Lendacky@amd.com, keir@xen.org, Jan Beulich <JBeulich@suse.com>, andrew.cooper3@citrix.com, xen-devel@lists.xen.org, Suravee.Suthikulpanit@amd.com
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On 4/29/2014 7:40 PM, Boris Ostrovsky wrote:
> On 04/29/2014 05:33 PM, Aravind Gopalakrishnan wrote:
>> On 4/29/2014 3:02 AM, Jan Beulich wrote:
>>>>>> On 28.04.14 at 18:35, <aravind.gopalakrishnan@amd.com> wrote:
>>>> +static bool_t verify_patch_size(uint32_t patch_size)
>>>> +{
>>>> +    uint32_t max_size;
>>>> +
>>>> +#define F1XH_MPB_MAX_SIZE 2048
>>>> +#define F14H_MPB_MAX_SIZE 1824
>>>> +#define F15H_MPB_MAX_SIZE 4096
>>>> +#define F16H_MPB_MAX_SIZE 3458
>>> Out of mere curiosity - what makes these numbers this odd? The last
>>> one isn't even divisible by 4.
>>
>> I don't know..
>> (+Boris) : any ideas?
>>
>
> No,  I suspect some sort of design constraint. But the number is 
> correct, I can confirm it (for what it's worth).
>
> I am BTW not sure I understand the reason for verifying patch size. If 
> you are concerned about patch/blob corruption then IIRC HW will verify 
> the patch anyway and will refuse to load it if doesn't pass HW's tests.

bkdg's mention something about HW performing some 'consistency checks'. 
A check to verify max_size could very well be one among them..
But just to be on safer side, we can have this extra sanity check in SW 
before applying the patch

-Aravind.