Re: [Xen-devel] [PATCH v8 03/16] microcode/intel: extend microcode_update_match()

[Chao Gao <chao.gao@xxxxxxxxx>]

On Fri, Aug 02, 2019 at 01:29:14PM +0000, Jan Beulich wrote:
>On 01.08.2019 12:22, Chao Gao wrote:
>> --- a/xen/arch/x86/microcode_intel.c
>> +++ b/xen/arch/x86/microcode_intel.c
>> @@ -134,14 +134,35 @@ static int collect_cpu_info(unsigned int cpu_num, 
>> struct cpu_signature *csig)
>>       return 0;
>>   }
>>   
>> -static inline int microcode_update_match(
>> -    unsigned int cpu_num, const struct microcode_header_intel *mc_header,
>> -    int sig, int pf)
>> +static enum microcode_match_result microcode_update_match(
>> +    const struct microcode_header_intel *mc_header, unsigned int sig,
>> +    unsigned int pf, unsigned int rev)
>>   {
>> -    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu_num);
>> -
>> -    return (sigmatch(sig, uci->cpu_sig.sig, pf, uci->cpu_sig.pf) &&
>> -            (mc_header->rev > uci->cpu_sig.rev));
>> +    const struct extended_sigtable *ext_header;
>> +    const struct extended_signature *ext_sig;
>> +    unsigned long data_size = get_datasize(mc_header);
>> +    unsigned int i;
>> +    const void *end = (const void *)mc_header + get_totalsize(mc_header);
>> +
>> +    if ( sigmatch(sig, mc_header->sig, pf, mc_header->pf) )
>> +        return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
>
>Both here and ...
>
>> +    ext_header = (const void *)(mc_header + 1) + data_size;
>> +    ext_sig = (const void *)(ext_header + 1);
>> +
>> +    /*
>> +     * Make sure there is enough space to hold an extended header and enough
>> +     * array elements.
>> +     */
>> +    if ( (end < (const void *)ext_sig) ||
>> +         (end < (const void *)(ext_sig + ext_header->count)) )
>> +        return MIS_UCODE;
>> +
>> +    for ( i = 0; i < ext_header->count; i++ )
>> +        if ( sigmatch(sig, ext_sig[i].sig, pf, ext_sig[i].pf) )
>> +            return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
>
>... here there's again an assumption that there's strict ordering
>between blobs, but as mentioned in reply to a later patch of an
>earlier version this isn't the case. Therefore the function can't
>be used to compare two arbitrary blobs, it may only be used to
>compare a blob with what is already loaded into a CPU. I think it
>is quite important to mention this restriction in a comment ahead
>of the function.
>
>The code itself looks fine to me, and a comment could perhaps be
>added while committing; with such a comment

Agree. Because there will be a version 9, I can add a comment.

>Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks.
Chao

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