mirrors/crosvm
1
0
Fork 0
mirror of https://chromium.googlesource.com/crosvm/crosvm synced 2024-11-24 20:48:55 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions
crosvm/seccomp/README.md
Alexandre Courbot c553d1c283 seccomp: define naming rules for policy files 
We are going to use separate policy files per device for the following scenarios:

1) Regular in-VMM virtio device,
2) Virtio device over vhost-user,
3) Virtio device over Vvu.

Each of these scenarios require slightly different policies as a jailed
device process needs to allow not only the system calls necessary for
the device to function, but also those required by the virtio transport
in use.

This CL adds a README.md file to the seccomp directory that details the
naming and policy inclusion rules, and updates the serial, xhci and
coiommu policies to follow the naming scheme.

Vhost-user and VVU policy files will be added along with support for
jailing devices when they are in use.

BUG=b:217480043
TEST=serial device works with `crosvm run`.

Change-Id: I6d454aa6e05d00691fe3346e822ed1fc7b24aed8
Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3706490
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
2022-06-17 04:35:09 +00:00

2.1 KiB
Raw Blame History

Policy files for crosvm

This folder holds the seccomp policies for crosvm devices, organized by architecture.

Each crosvm device can run within its owned jailed process. A jailed process is only able to perform the system calls specified in the seccomp policy file the jail has been created with, which improves security as a rogue process cannot perform any system call it wants.

Each device can run from different contexts, which require a different set of authorized system calls. This file explains how the policy files are named in order to allow these various scenario.

Naming conventions

Since Minijail only allows for one level of policy inclusion, we need to be a little bit creative in order to minimize policy duplication.

  • common_device.policy contains a set of syscalls that are common to all devices, and is never loaded directly - only included from other policy files.
  • foo.policy contains the set of syscalls that device foo is susceptible to use, regardless of the underlying virtio transport. This policy is also never loaded directly.
  • foo_device.policy is the policy that is loaded when device foo is used as an in-VMM (i.e. regular virtio) device. It will generally simply include common_device.policy as well as foo.policy.

When using vhost-user, the virtio protocol needs to be sent over a different medium, e.g. a Unix socket. Supporting this transport requires some extra system calls after the device is jailed, and thus dedicated policies:

  • vhost_user.policy contains the set of syscalls required by the regular (i.e. socket-based) vhost-user listener. It is never loaded directly.
  • vvu.policy contains the set of syscalls required by the VFIO-based vhost-user (aka Virtio-Vhost-User) listener. It is also never loaded directly.
  • foo_device_vhost_user.policy is the policy that is loaded when device foo is used as a regular vhost-user device. It will generally include common_device.policy, vhost_user.policy and foo.policy.
  • foo_device_vvu.policy is the policy that is loaded when device foo is used as a VVU device. It will generally include common_device.policy, vvu.policy and foo.policy.