Re: [Xen-devel] [PATCH V2] x86, amd_ucode: Verify max allowed patch size before apply

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

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@xxxxxxx> 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.



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