linux-kernel - Re: [PATCH 1/2] x86, microcode: Do Intel microcode revision check signed

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Message-ID: <20131210153000.GA3804@phenom.dumpdata.com>
Date:	Tue, 10 Dec 2013 10:30:00 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86, microcode: Do Intel microcode revision check
 signed

On Fri, Dec 06, 2013 at 01:04:02PM -0800, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> The Intel SDM Vol 3 9.11.1 Microcode update states that
> the update revision field is signed. However we do the comparison
> unsigned, as the comparison gets promoted.
> 
> Use a cast to really do a signed comparison of the microcode
> revision.

Why not just update the struct?
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kernel/microcode_intel_lib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/microcode_intel_lib.c b/arch/x86/kernel/microcode_intel_lib.c
> index ce69320..68503d1 100644
> --- a/arch/x86/kernel/microcode_intel_lib.c
> +++ b/arch/x86/kernel/microcode_intel_lib.c
> @@ -41,7 +41,7 @@ update_match_cpu(unsigned int csig, unsigned int cpf,
>  int
>  update_match_revision(struct microcode_header_intel *mc_header, int rev)
>  {
> -	return (mc_header->rev <= rev) ? 0 : 1;
> +	return ((int)mc_header->rev <= rev) ? 0 : 1;
>  }
>  
>  int microcode_sanity_check(void *mc, int print_err)
> -- 
> 1.8.3.1
> 
> --
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