Re: [Patch v2 2/4] x86/speculation: Provide application property based STIBP protection

[Thomas Gleixner]

On Tue, 25 Sep 2018, Tim Chen wrote:

> This patch provides an application property based spectre_v2

# git grep 'This patch' Documentation/process/

> protection with STIBP against attack from another app from

s/app/application/ please. This is not android.

> a sibling hyper-thread.  For security sensitive non-dumpable
> app, STIBP will be turned on before switching to it for Intel
> processors vulnerable to spectre_v2.

What has this to do with Intel processors?

> -static __always_inline void intel_set_ssb_state(unsigned long tifn)
> +static __always_inline void set_spec_ctrl_state(unsigned long tifn)
>  {
> -	u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
> +	u64 msr = x86_spec_ctrl_base;
> +
> +	if (static_cpu_has(X86_FEATURE_SSBD))
> +		msr |= ssbd_tif_to_spec_ctrl(tifn);
> +
> +	if (cpu_smt_control == CPU_SMT_ENABLED)
> +		msr |= stibp_tif_to_spec_ctrl(tifn);

Oh no. We are not adding yet another conditional into switch to. Either
that's done unconditionally or this wants to have a static key.

>  	wrmsrl(MSR_IA32_SPEC_CTRL, msr);

Thanks,

	tglx