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

[Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>]

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?
>> @@ -123,8 +151,17 @@ static bool_t microcode_fits(const struct microcode_amd *mc_amd, int cpu)
>>       if ( (mc_header->processor_rev_id) != equiv_cpu_id )
>>           return 0;
>>   
>> +    if ( !verify_patch_size(mc_amd->mpb_size) )
>> +    {
>> +        printk(XENLOG_DEBUG "microcode: patch size mismatch\n");
>> +        return -E2BIG;
>> +    }
>> +
>>       if ( mc_header->patch_id <= uci->cpu_sig.rev )
>> -        return 0;
>> +    {
>> +        printk(XENLOG_DEBUG "microcode: patch is already at required level or greater.\n");
>> +        return -EEXIST;
>> +    }
>>   
>>       printk(KERN_DEBUG "microcode: CPU%d found a matching microcode "
>>              "update with version %#x (current=%#x)\n",
> Honestly I'm rather hesitant to accept further generally useless
> messages, no matter that they get printed at KERN_DEBUG only. I'd
> much rather see these as well as the existing ones to be converted
> to pr_debug(), thus easily enabled if someone really needs to do
> debugging here. That's mainly because I (and I suppose other
> developers do so to) try to run with loglvl=all wherever possible,
> yet already on the 2x4-core box (not to speak of the newer 2x12-
> core one) I find these rather annoying.

Hmm, Okay. I'll work on this and send an updated version..

> And btw - now that you switch microcode_fits() back to returning
> int (and -errno values) you would need to alter other return paths
> to. That said, I don't really see why this return type change is
> needed, the more that ...
>
>> @@ -319,7 +356,7 @@ static int cpu_request_microcode(int cpu, const void *buf, size_t bufsize)
>>       while ( (error = get_ucode_from_buffer_amd(mc_amd, buf, bufsize,
>>                                                  &offset)) == 0 )
>>       {
>> -        if ( microcode_fits(mc_amd, cpu) )
>> +        if ( (error = microcode_fits(mc_amd, cpu)) > 0 )
>>           {
>>               error = apply_microcode(cpu);
>>               if ( error )
> ... this still is a behavioral change: There may now be -EEXIST
> bubbling up to do_microcode_update(), i.e. a hypercall that
> previously succeeded under the same conditions (not applying
> anything after all is not an error, particularly if that's just because
> what the CPU had was already at or above the level that we try
> loading).

Hmm. Yeah, true, but I thought at least in some situations we could save 
the trouble of parsing
through the fw image once again..
Maybe this can be addressed by simplifying microcode_init someday

Let me go back to returning bool_t from microcode_fits() and

+    if ( !verify_patch_size(mc_amd->mpb_size) )
+    {
	 ...
+        return 0;
+    }
+
      if ( mc_header->patch_id <= uci->cpu_sig.rev )
+    {
	 ...
+        return 0;
+    }


Thanks,
-Aravind.