Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

[Thomas Gleixner]

Tim,

On Fri, 16 Nov 2018, Tim Chen wrote:

> Add new protection modes for Spectre v2 mitigations against
> Spectre v2 attacks on user processes.  There are three modes:
> 
> 	strict mode:
> 	In this mode, IBPB and STIBP are deployed full
> 	time to protect all processes.
> 
> 	lite mode:
> 	In this mode, IBPB and STIBP are only deployed on
> 	processes marked with TIF_STIBP flag.
> 
> 	none mode:
> 	In this mode, no mitigations are deployed.
>
> The protection mode can be specified by the spectre_v2_app2app
> boot parameter with the following semantics:
> 
> spectre_v2_app2app=
> 	off    - Turn off mitigation
> 	lite   - Protect processes which are marked non-dumpable
> 	strict - Protect all processes
> 	auto   - Kernel selects the mode

Is there any reason why we need yet another naming convention?

pti= 				on, off, auto

spectre_v2=			on, off, auto

spec_store_bypass_disable =	on, off, auto, prctl, seccomp


> 	Not specifying this option is equivalent to
> 	spectre_v2_app2app=auto.

For better understanding it's nowhere documented what auto does.

> +	spectre_v2_app2app=
> +			[X86] Control mitigation of Spectre variant 2
> +		        application to application (indirect branch speculation)
> +			vulnerability.
> +
> +			off    - Unconditionally disable mitigations
> +			lite   - Protect tasks which have requested restricted
> +				 indirect branch speculation via the
> +				 PR_SET_SPECULATION_CTRL prctl(). 
> +			strict - Protect all processes
> +			auto   - Kernel selects the mode
> +
> +			Not specifying this option is equivalent to
> +			spectre_v2_app2app=auto.
> +
> +			Setting spectre_v2=off will also turn off this mitigation.
> +
> +			Setting spectre_v2=on implies unconditionally enabling
> +			this mitigation.

Can we please have a full documentation for all the spectre_v2 stuff
similar to l1tf?

Thanks,

	tglx