Messages in this thread |  | | Date | Sun, 7 Jan 2018 13:06:43 -0500 | From | Theodore Ts'o <> | Subject | Re: Proposal: CAP_PAYLOAD to reduce Meltdown and Spectre mitigation costs |
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On Sun, Jan 07, 2018 at 02:51:59PM +0200, Avi Kivity wrote: > > 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).
In the classical (as defined by the withdrawn Posix draft spec) capaibilities model, if you have a setuid root process it gets all the capabilities, and capabilities are used to limit what privileges a root process. Hence using strict capabilities, any setuid root process would have CAP_PAYLOAD.
Linux has extensions which allow you to have capability bound which capabilities that can be obtained by a process, so you _could_ make it work, but it just seems like an bad fit, since it's not strictly speaking a root-owned privilege. It's more like a configuration setting, and so modulating it via cgroups attribute seems to make a lot more sense --- it's certainly (IMHO) less confusing than trying to ab(use) the capabilities system and its extensions in this fashion.
- Ted
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