Re: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors

[Borislav Petkov]

On Tue, Dec 26, 2017 at 11:43:54PM -0600, Tom Lendacky wrote:
> AMD processors are not subject to the types of attacks that the kernel
> page table isolation feature protects against.  The AMD microarchitecture
> does not allow memory references, including speculative references, that
> access higher privileged data when running in a lesser privileged mode
> when that access would result in a page fault.
> 
> Disable page table isolation by default on AMD processors by not setting
> the X86_BUG_CPU_INSECURE feature, which controls whether X86_FEATURE_PTI
> is set.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/common.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index c47de4e..7d9e3b0 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -923,8 +923,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>  
>  	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
>  
> -	/* Assume for now that ALL x86 CPUs are insecure */
> -	setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
> +	if (c->x86_vendor != X86_VENDOR_AMD)
> +		setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
>  
>  	fpu__init_system(c);

Reviewed-by: Borislav Petkov <bp@xxxxxxx>

-- 
Regards/Gruss,
    Boris.

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