linux-kernel - Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors

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Date:   Wed, 24 Jan 2018 17:07:03 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel
 processors

>  
> +static const __initdata struct x86_cpu_id cpu_no_meltdown[] = {
> +	{ X86_VENDOR_AMD },
> +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CEDARVIEW, X86_FEATURE_ANY },
> +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CLOVERVIEW, X86_FEATURE_ANY },
> +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_LINCROFT, X86_FEATURE_ANY },
> +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PENWELL, X86_FEATURE_ANY },
> +	{ X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PINEVIEW, X86_FEATURE_ANY },

As Linus said this should be no_specualtion[]

If we are going to capture 32bit here with your lines below I'll send you
an update at some point with all the 32bit families hunted down (some
like the CE4100 may take a bit of hunting)


> +	{ X86_VENDOR_ANY, 5 },

AND K5 speculates, Cyrix 6x86 speculates, IDT WinChip does not. I think
this should be

X86_VENDOR_ANY, 4
X86_VENDOR_INTEL, 5,
X86_VENDOR_CENTAUR, 5,


> +static bool __init early_cpu_vulnerable_meltdown(struct cpuinfo_x86 *c)
> +{
> +	u64 ia32_cap = 0;
> +
> +	if (x86_match_cpu(cpu_no_meltdown))
> +                return false;

These processors are also not vulnerable to spectre, so this patch
doesn't set the other flags correctly - that's why we need two levels of
logic here. "Bonnell" and "Saltwell" uarch Atom processors are not
vulnerable to Meltdown or Spectre, neithr is a 486, Pentium, Quark etc.



> +
> +	if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
> +		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> +	if (ia32_cap & ARCH_CAP_RDCL_NO)
> +		return false;
> +
> +	return true;
> +}
> +
>  /*
>   * Do minimum CPU detection early.
>   * Fields really needed: vendor, cpuid_level, family, model, mask,
> @@ -900,9 +929,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>  
>  	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
>  
> -	if (c->x86_vendor != X86_VENDOR_AMD)
> +	if (early_cpu_vulnerable_meltdown(c))
>  		setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
> -
>  	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
>  	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
>  
> -- 
> 2.14.3