linux-kernel - Re: x86/microcode/intel: Division by zero panic in 4.9.79 and 4.4.114

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Date:   Wed, 7 Feb 2018 19:12:54 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Rolf Neugebauer <rolf.neugebauer@...ker.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Jia Zhang <zhang.jia@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: x86/microcode/intel: Division by zero panic in 4.9.79 and 4.4.114

On Wed, Feb 07, 2018 at 04:31:59PM +0000, Rolf Neugebauer wrote:
>  arch/x86/kernel/cpu/microcode/core.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/core.c
> b/arch/x86/kernel/cpu/microcode/core.c
> index b3e94ef461fd..1b3e0aa4c511 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -44,7 +44,7 @@
> 
>  static struct microcode_ops    *microcode_ops;
> 
> -static bool dis_ucode_ldr;
> +static bool dis_ucode_ldr = true;
> 
>  static int __init disable_loader(char *str)
>  {
> @@ -81,6 +81,7 @@ struct cpu_info_ctx {
> 
>  static bool __init check_loader_disabled_bsp(void)
>  {
> +       u32 a, b, c, d;
>  #ifdef CONFIG_X86_32
>         const char *cmdline = (const char *)__pa_nodebug(boot_command_line);
>         const char *opt     = "dis_ucode_ldr";
> @@ -93,8 +94,23 @@ static bool __init check_loader_disabled_bsp(void)
>         bool *res = &dis_ucode_ldr;
>  #endif
> 
> -       if (cmdline_find_option_bool(cmdline, option))
> -               *res = true;
> +       if (!have_cpuid_p())
> +               return *res;

That might cause an issue, see 1f161f67a272c. Might wanna backport that
commit too, just in case, for those old CPUID-less geodes.

The rest looks ok.

-- 
Regards/Gruss,
    Boris.

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