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

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

On 4/24/2014 3:26 PM, Andrew Cooper wrote:
> On 24/04/14 20:54, Aravind Gopalakrishnan wrote:
>>   
>> -static bool_t microcode_fits(const struct microcode_amd *mc_amd, int cpu)
>> +static bool_t verify_patch_size(uint32_t patch_size)
>> +{
>> +    uint8_t family;
>> +    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
>> +
>> +    family = boot_cpu_data.x86;
>> +    switch (family)
> You can drop the family variable and just switch on boot_cpu_data.x86

Noted.
>> +static int microcode_fits(const struct microcode_amd *mc_amd, int cpu)
>>   {
>>       struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
>>       const struct microcode_header_amd *mc_header = mc_amd->mpb;
>> @@ -118,19 +151,25 @@ static bool_t microcode_fits(const struct microcode_amd *mc_amd, int cpu)
>>       }
>>   
>>       if ( !equiv_cpu_id )
>> -        return 0;
>> +        return -EINVAL;
>>   
>>       if ( (mc_header->processor_rev_id) != equiv_cpu_id )
>> -        return 0;
>> +        return -EINVAL;
>> +
>> +    if ( !verify_patch_size(mc_amd->mpb_size) )
>> +    {
>> +        printk(KERN_ERR "microcode: patch size mismatch\n");
>> +        return -EINVAL;
> XENLOG_ERR "microcode patch size too large"
> return -E2BIG;
>
> And is this really worth being an error as opposed to a warning, or
> frankly even just debug? It is presumably one of N possible blobs in the
> hypercall.

Right. Modified it to use XENLOG_DEBUG instead.
>>   
>>   static int apply_microcode(int cpu)
>> @@ -319,7 +358,8 @@ 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) )
>> +        error = microcode_fits(mc_amd, cpu);
>> +        if ( !error )
>>           {
>>               error = apply_microcode(cpu);
>>               if ( error )
>> @@ -329,6 +369,11 @@ static int cpu_request_microcode(int cpu, const void *buf, size_t bufsize)
>>   
>>           last_offset = offset;
>>   
>> +        if ( error == -EEXIST ) {
>> +            printk(KERN_DEBUG "microcode: patch is already at required level or greater.\n");
>> +            break;
> You can't break from the loop here.  What if a subsequent blob in the
> buffer contains a newer piece of microcode?
>     

Right. Didn't think about that. Sorry..

But I ran into larger issues here:
Since we don't break on the first match and continue to parse the entire 
fw image till the very end;
*and* since I modified the error handling around 'microcode_fits' thus:

if ( (mc_header->processor_rev_id) != equiv_cpu_id )

-return 0;

+return -EINVAL;

+

The last returned error val is '-22' which is bubbled up to microcode.c. 
'microcode_presmp_init' as a result
flushes out ucode_blob or NULL-ifies ucode_mod_map.

Which means 'microcode_init' returns early as it can't validate 
ucode_mod.mod_end or ucode_blob.size
Now, this breaks original functionality (sorry for catching this late), 
*but*
doesn't cause any problem to updating(,applying) ucode patches to cpus 
as we apply the patches during
'microcode_resume_cpu' anyway.  (which is why I thought at first all is 
fine)

Could someone please help me understand why there are two initcalls - 
'microcode_presmp_init' && 'microcode_init'
that perform the same tasks?

It results in these functions - 'collect_cpu_info', 
'cpu_request_microcode' to run a second time through 'microcode_init'
when we have already accomplished the job of updating cpu with microcode 
patches
through 'microcode_presmp_init' and 'microcode_resume_cpu'

If there is particular reason for 'microcode_init''s existence, then 
I'll modify the patch so that the error handling around 'microcode_fits'
is not altered. But if not, then I simply have to just remove the 
'break' statement.

Thanks,
-Aravind.