linux-kernel - Re: [PATCH v1] x86/microcode: Handle negative microcode revisions

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Message-ID: <20181020083742.GA28301@zn.tnic>
Date:   Sat, 20 Oct 2018 10:37:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1] x86/microcode: Handle negative microcode revisions

On Fri, Oct 19, 2018 at 05:11:37PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> The Intel ucode revision space is unsigned. Inside Intel there are special

s/ucode/microcode/g

> microcodes that have the highest bit set, and they are considered to have

s/microcodes/microcode revisions/g

> a higher revision than any microcodes that don't have this bit set.
> 
> The function comparing the microcodes in the Linux driver compares
> u32 with int, which ends up being signed extended to long on 64bit
> systems. This results in these highest bit set microcodes not loading
> because their revision appears negative and smaller than the
> existing microcode.
> 
> Change the comparison to unsigned. With that the loading works
> as expected.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/microcode/intel.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 16936a24795c..e95cebdd5993 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -93,7 +93,7 @@ static int find_matching_signature(void *mc, unsigned int csig, int cpf)
>  /*
>   * Returns 1 if update has been found, 0 otherwise.
>   */
> -static int has_newer_microcode(void *mc, unsigned int csig, int cpf, int new_rev)
> +static int has_newer_microcode(void *mc, unsigned int csig, int cpf, unsigned new_rev)

I'm gonna let you run checkpatch yourself to find out what the problem
here is.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.