Re: [Xen-devel] [PATCH v10 01/16] microcode/intel: extend microcode_update_match()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.09.2019 09:22, Chao Gao wrote:
> --- a/xen/arch/x86/microcode_intel.c
> +++ b/xen/arch/x86/microcode_intel.c
> @@ -134,21 +134,11 @@ 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 int microcode_sanity_check(const void *mc)
>  {
> -    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));
> -}
> -
> -static int microcode_sanity_check(void *mc)
> -{
> -    struct microcode_header_intel *mc_header = mc;
> -    struct extended_sigtable *ext_header = NULL;
> -    struct extended_signature *ext_sig;
> +    const struct microcode_header_intel *mc_header = mc;
> +    const struct extended_sigtable *ext_header = NULL;
> +    const struct extended_signature *ext_sig;
>      unsigned long total_size, data_size, ext_table_size;
>      unsigned int ext_sigcount = 0, i;
>      uint32_t sum, orig_sum;
> @@ -234,6 +224,42 @@ static int microcode_sanity_check(void *mc)
>      return 0;
>  }
>  
> +/* Check an update against the CPU signature and current update revision */
> +static enum microcode_match_result microcode_update_match(
> +    const struct microcode_header_intel *mc_header, unsigned int cpu)
> +{
> +    const struct extended_sigtable *ext_header;
> +    const struct extended_signature *ext_sig;
> +    unsigned int i;
> +    struct ucode_cpu_info *uci = &per_cpu(ucode_cpu_info, cpu);
> +    unsigned int sig = uci->cpu_sig.sig;
> +    unsigned int pf = uci->cpu_sig.pf;
> +    unsigned int rev = uci->cpu_sig.rev;
> +    unsigned long data_size = get_datasize(mc_header);
> +    const void *end = (const void *)mc_header + get_totalsize(mc_header);
> +
> +    ASSERT(!microcode_sanity_check(mc_header));
> +    if ( sigmatch(sig, mc_header->sig, pf, mc_header->pf) )
> +        return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;
> +
> +    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;

With you now assuming that the blob has previously passed
microcode_sanity_check(), this only needs to be

    if ( (end <= (const void *)ext_sig) )
        return MIS_UCODE;

now afaict.

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
preferably with this adjustment (assuming you agree).

Jan

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