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Starting with v4.18, the Linux kernel provides the rseq syscall which is a mechanism for fast userspace task synchronization. Starting with v2.35 glibc uses the new syscall, if it exists, to gain some performance improvements, so we need to update the policy files to allow it. Even on older kernels where rseq is not supported, glibc will still probe for its existence by expecting an -ENOSYS response. BUG=b:235960683 TEST=Local builds against glibc 2.35 Change-Id: I704f2fbf2b058c3a4c3269c7441c3a7324012f8a Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3763901 Commit-Queue: Manoj Gupta <manojgupta@chromium.org> Owners-Override: Dominick Ng <dominickn@google.com> Reviewed-by: Allen Webb <allenwebb@google.com> Reviewed-by: Dennis Kempin <denniskempin@google.com> Tested-by: Manoj Gupta <manojgupta@chromium.org> |
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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.policycontains a set of syscalls that are common to all devices, and is never loaded directly - only included from other policy files.foo.policycontains the set of syscalls that devicefoois susceptible to use, regardless of the underlying virtio transport. This policy is also never loaded directly.foo_device.policyis the policy that is loaded when devicefoois used as an in-VMM (i.e. regular virtio) device. It will generally simply includecommon_device.policyas well asfoo.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.policycontains the set of syscalls required by the regular (i.e. socket-based) vhost-user listener. It is never loaded directly.vvu.policycontains 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.policyis the policy that is loaded when devicefoois used as a regular vhost-user device. It will generally includecommon_device.policy,vhost_user.policyandfoo.policy.foo_device_vvu.policyis the policy that is loaded when devicefoois used as a VVU device. It will generally includecommon_device.policy,vvu.policyandfoo.policy.