Re: [Xen-devel] [PATCH v7 02/10] microcode/intel: extend microcode_update_match()

From: "Jan Beulich" <JBeulich@suse.com>
To: "Chao Gao" <chao.gao@intel.com>
Cc: Sergey Dyasli <sergey.dyasli@citrix.com>,
	Ashok Raj <ashok.raj@intel.com>, WeiLiu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH v7 02/10] microcode/intel: extend microcode_update_match()
Date: Tue, 04 Jun 2019 08:39:15 -0600	[thread overview]
Message-ID: <5CF682930200007800235268@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <1558945891-3015-3-git-send-email-chao.gao@intel.com>

>>> On 27.05.19 at 10:31, <chao.gao@intel.com> wrote:
> --- a/xen/arch/x86/microcode_intel.c
> +++ b/xen/arch/x86/microcode_intel.c
> @@ -134,14 +134,28 @@ 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);
> +    const struct extended_sigtable *ext_header;
> +    const struct extended_signature *ext_sig;
> +    unsigned long data_size = get_datasize(mc_header);
> +    unsigned int i;
> +
> +    if ( sigmatch(sig, mc_header->sig, pf, mc_header->pf) )
> +        return (mc_header->rev > rev) ? NEW_UCODE : OLD_UCODE;

As indicated before, I think you would better also provide an "equal"
indication. Iirc I've told you that I have one system where the cores
get handed over from the BIOS in an inconsistent state (only core
has ucode loaded). Hence we'd want to be able to also _store_
ucode matching that found on CPU 0, without actually want to _load_
it there.

> -    return (sigmatch(sig, uci->cpu_sig.sig, pf, uci->cpu_sig.pf) &&
> -            (mc_header->rev > uci->cpu_sig.rev));
> +    if ( get_totalsize(mc_header) == (data_size + MC_HEADER_SIZE) )
> +        return MIS_UCODE;

Okay, you're tightening the original <= to == here. But if you're
already tightening things, why don't you make sure you actually
have enough data to ...

> +    ext_header = (const void *)(mc_header + 1) + data_size;

... hold an extended header, and then also to hold ...

> +    ext_sig = (const void *)(ext_header + 1);
> +    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;

... enough array elements?

Jan

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