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

[Tim Chen]

On 11/19/2018 05:32 AM, Thomas Gleixner wrote:
> 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

The "on" option is set by spectre_v2=on so is not specified here.
What will you like to name the "lite" and "strict" option instead?

> 
> 
>> 	Not specifying this option is equivalent to
>> 	spectre_v2_app2app=auto.
> 
> For better understanding it's nowhere documented what auto does.

I'll add the documentation.

> 
>> +	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?
> 

Sure.  Can we do that as a separate patch?  I'll need some time 
and internal review for any spectre_v2 documentation that's produced.

Tim