platform_system_sepolicy/private/fastbootd.te
Gil Cukierman 214294ce75 Add SELinux Policy For io_uring
Brings in the io_uring class and associated restrictions and adds a new
macro, `io_uring_use`, to sepolicy.

In more detail, this change:

* Adds a new macro expands to ensure the domain it is passed can undergo a
type transition to a new type, `<domain>_iouring`, when the anon_inode
being accessed is labeled `[io_uring]`. It also allows the domain to
create, read, write, and map the io_uring anon_inode.

* Adds the ability for a domain to use the `IORING_SETUP_SQPOLL` flag
during `io_uring_setup` so that a syscall to `io_uring_enter` is not
required by the caller each time it wishes to submit IO. This can be
enabled securely as long as we don't enable sharing of io_uring file
descriptors across domains. The kernel polling thread created by `SQPOLL`
will inherit the credentials of the thread that created the io_uring [1].

* Removes the selinux policy that restricted all domains that make use of
the `userfault_fd` macro from any `anon_inode` created by another domain.
This is overly restrictive, as it prohibits the use of two different
`anon_inode` use cases in a single domain e.g. userfaultfd and io_uring.

This change also replaces existing sepolicy in fastbootd and snapuserd
that enabled the use of io_uring.

[1] https://patchwork.kernel.org/project/linux-security-module/patch/163159041500.470089.11310853524829799938.stgit@olly/

Bug: 253385258
Test: m selinux_policy
Test: cd external/liburing; mm; atest liburing_test; # requires WIP CL ag/20291423
Test: Manually deliver OTAs (built with m dist) to a recent Pixel device
and ensure snapuserd functions correctly (no io_uring failures)

Change-Id: I96f38760b3df64a1d33dcd6e5905445ccb125d3f
2023-01-27 11:44:59 -05:00

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typeattribute fastbootd coredomain;
# The allow rules are only included in the recovery policy.
# Otherwise fastbootd is only allowed the domain rules.
recovery_only(`
# Reboot the device
set_prop(fastbootd, powerctl_prop)
# Read serial number of the device from system properties
get_prop(fastbootd, serialno_prop)
# Set sys.usb.ffs.ready.
get_prop(fastbootd, ffs_config_prop)
set_prop(fastbootd, ffs_control_prop)
userdebug_or_eng(`
get_prop(fastbootd, persistent_properties_ready_prop)
')
set_prop(fastbootd, gsid_prop)
# Determine allocation scheme (whether B partitions needs to be
# at the second half of super.
get_prop(fastbootd, virtual_ab_prop)
get_prop(fastbootd, snapuserd_prop)
# Needed for TCP protocol
allow fastbootd node:tcp_socket node_bind;
allow fastbootd port:tcp_socket name_bind;
allow fastbootd self:tcp_socket { create_socket_perms_no_ioctl listen accept };
# Start snapuserd for merging VABC updates
set_prop(fastbootd, ctl_snapuserd_prop)
# Needed to communicate with snapuserd to complete merges.
allow fastbootd snapuserd_socket:sock_file write;
allow fastbootd snapuserd:unix_stream_socket connectto;
allow fastbootd dm_user_device:dir r_dir_perms;
# Get fastbootd protocol property
get_prop(fastbootd, fastbootd_protocol_prop)
# Mount /metadata to interact with Virtual A/B snapshots.
allow fastbootd labeledfs:filesystem { mount unmount };
# Needed for reading boot properties.
allow fastbootd proc_bootconfig:file r_file_perms;
# Let this domain use the hal fastboot service
binder_use(fastbootd)
hal_client_domain(fastbootd, hal_fastboot)
')
# This capability allows fastbootd to circumvent memlock rlimits while using
# io_uring. An Alternative would be to up the memlock rlimit for the fastbootd service.
allow fastbootd self:capability ipc_lock;
io_uring_use(fastbootd)