[MODERATED] Re: ***UNCHECKED*** [patch 3/8] [PATCH v1.3.1 3/7] Linux Patch 3

[Borislav Petkov <bp@suse.de>]

On Thu, Apr 12, 2018 at 10:26:52PM -0400, speck for konrad.wilk_at_oracle.com wrote:
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 561cb228605a..73f76d0f5181 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -72,6 +72,9 @@ void __init check_bugs(void)
>  	 */
>  	if (!direct_gbpages)
>  		set_memory_4k((unsigned long)__va(0), 1);
> +
> +	if (mdd_at_boot())
> +		wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_MDD);

You can't do this on the common path as that would explode on !Intel.

Instead, move that check to init_intel().

And add to init_amd_zn() code reading MSR 0xc0011020, setting bit 10 to
1b and then writing it back in the mdd_at_boot() case. We have a define
for that MSR already - MSR_AMD64_LS_CFG.

>  
> @@ -317,7 +320,14 @@ static void __init spectre_v2_select_mitigation(void)
>  #undef pr_fmt
>  #define pr_fmt(fmt)     "MDD: " fmt
>  
> -static enum md_mitigation md_mode = MD_NONE;
> +enum md_mitigation md_mode = MD_NONE;
> +/* When switching from lower privilege level (cpl3) to higher (cpl0). */
> +u64 spec_ctrl_priv;
> +EXPORT_SYMBOL_GPL(spec_ctrl_priv);
> +
> +/* When switching from higher to lower privilege level. */
> +u64 spec_ctrl_unpriv;
> +EXPORT_SYMBOL_GPL(spec_ctrl_unpriv);

I don't like exporting some arbitrary variables to the rest of the
kernel. Do accessors instead pls.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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