Re: [Patch v2 4/4] x86/speculation: Add prctl to control indirect branch speculation per process

[Ingo Molnar]

* Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote:

> To migitgate possible app to app attack from branch target buffer poisoning,
> a new prctl is provided to control branch speculation for applications in
> user app.  The following interfaces are provided:

s/migitgate
 /mitigate

> 
> prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
> - Disable branch target speculation to protect against app to app
> style attack using IBPB and STIBP
> 
> prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
> - Allow branch target speculation, no mitigation for Spectre V2
> 
> prctl(PR_GET_SPECULATION_CTRL, PR_INDIR_BRANCH, 0, 0, 0)
> - Query the indirect branch speculation restriction on a process

Well 'a process' is always 'the current process' in this case, right?

> -			lite   - only turn on mitigation for non-dumpable processes
> +			lite   - turn on mitigation for non-dumpable processes
> +				 or processes that has indirect branch restricted
> +				 via prctl's PR_SET_SPECULATION_CTRL option

s/or processes that has indirect
 /or processes that have been indirect

?

> +	/*
> +	 * If being set on non-current task, delay setting the CPU
> +	 * mitigation until it is next scheduled.
> +	 * Use speculative_store_bypass_update will update SPEC_CTRL MSR
> +	 */
> +	if (task == current && update)
> +		speculative_store_bypass_update_current();

Did you mean:

	Call to speculative_store_bypass_update_current() will update SPEC_CTRL MSR

?


> -	 * For lite protection mode, we only protect the non-dumpable
> -	 * processes.
> +	 * For lite protection mode, we protect processes  
> +	 * where the user explicitly disable indirect branch
> +	 * speculation or mark the process as non-dumpable. 

s/where the user explicitly disable
 /where the user explicitly disables

?

Thanks,

	Ingo