Re: Proposal: CAP_PAYLOAD to reduce Meltdown and Spectre mitigation costs

[Avi Kivity]

On 01/07/2018 02:29 PM, Theodore Ts'o wrote:
> On Sun, Jan 07, 2018 at 11:16:28AM +0200, Avi Kivity wrote:
> > I think capabilities will work just as well with cgroups. The container
> > manager will set CAP_PAYLOAD to payload containers; and if those run an init
> > system or a container manager themselves, they'll drop CAP_PAYLOAD for all
> > process/sub-containers but their payloads.
> The reason why cgroups are better is Spectre can be used to steal
> information from within the same privilege level --- e.g., you could
> use Javascript to steal a user's Coindesk credentials or Lastpass
> data, which is going to be *way* more lucrative than trying to mine
> cryptocurrency in the sly in a user's browser.  :-)
>
> As a result, you probably want Spectre mitigations to be enabled in a
> root process --- which means capabilities aren't the right answer.

I don't see the connection. The browser wouldn't run with CAP_PAYLOAD set.

In a desktop system, only init retains CAP_PAYLOAD.

On a server that runs one application (and some supporting processes), 
only init and that one application have CAP_PAYLOAD (if the sysadmin 
makes it so).

On a containerized server that happens to run just one application, init 
will retain CAP_PAYLOAD, as well as the process in the container (if the 
sysadmin makes it so).

On a containerized server that happens to run just one application, 
which itself runs an init system, the two inits will retain CAP_PAYLOAD, 
as well as the application process (if the sysadmin makes it so).