sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 122 insertions, 0 deletions

diff --git a/security/apparmor/Kconfig b/security/apparmor/Kconfig
new file mode 100644
index 000000000..1e3bd4464
--- /dev/null
+++ b/security/apparmor/Kconfig
@@ -0,0 +1,122 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config SECURITY_APPARMOR
+	bool "AppArmor support"
+	depends on SECURITY && NET
+	select AUDIT
+	select SECURITY_PATH
+	select SECURITYFS
+	select SECURITY_NETWORK
+	default n
+	help
+	  This enables the AppArmor security module.
+	  Required userspace tools (if they are not included in your
+	  distribution) and further information may be found at
+	  http://apparmor.wiki.kernel.org
+
+	  If you are unsure how to answer this question, answer N.
+
+config SECURITY_APPARMOR_DEBUG
+	bool "Build AppArmor with debug code"
+	depends on SECURITY_APPARMOR
+	default n
+	help
+	  Build apparmor with debugging logic in apparmor. Not all
+	  debugging logic will necessarily be enabled. A submenu will
+	  provide fine grained control of the debug options that are
+	  available.
+
+config SECURITY_APPARMOR_DEBUG_ASSERTS
+	bool "Build AppArmor with debugging asserts"
+	depends on SECURITY_APPARMOR_DEBUG
+	default y
+	help
+	  Enable code assertions made with AA_BUG. These are primarily
+	  function entry preconditions but also exist at other key
+	  points. If the assert is triggered it will trigger a WARN
+	  message.
+
+config SECURITY_APPARMOR_DEBUG_MESSAGES
+	bool "Debug messages enabled by default"
+	depends on SECURITY_APPARMOR_DEBUG
+	default n
+	help
+	  Set the default value of the apparmor.debug kernel parameter.
+	  When enabled, various debug messages will be logged to
+	  the kernel message buffer.
+
+config SECURITY_APPARMOR_INTROSPECT_POLICY
+	bool "Allow loaded policy to be introspected"
+	depends on SECURITY_APPARMOR
+	default y
+	help
+	  This option selects whether introspection of loaded policy
+	  is available to userspace via the apparmor filesystem. This
+	  adds to kernel memory usage. It is required for introspection
+	  of loaded policy, and check point and restore support. It
+	  can be disabled for embedded systems where reducing memory and
+	  cpu is paramount.
+
+config SECURITY_APPARMOR_HASH
+	bool "Enable introspection of sha256 hashes for loaded profiles"
+	depends on SECURITY_APPARMOR_INTROSPECT_POLICY
+	select CRYPTO_LIB_SHA256
+	default y
+	help
+	  This option selects whether introspection of loaded policy
+	  hashes is available to userspace via the apparmor
+	  filesystem. This option provides a light weight means of
+	  checking loaded policy.  This option adds to policy load
+	  time and can be disabled for small embedded systems.
+
+config SECURITY_APPARMOR_HASH_DEFAULT
+       bool "Enable policy hash introspection by default"
+       depends on SECURITY_APPARMOR_HASH
+       default y
+       help
+	 This option selects whether sha256 hashing of loaded policy
+	 is enabled by default. The generation of sha256 hashes for
+	 loaded policy provide system administrators a quick way to
+	 verify that policy in the kernel matches what is expected,
+	 however it can slow down policy load on some devices. In
+	 these cases policy hashing can be disabled by default and
+	 enabled only if needed.
+
+config SECURITY_APPARMOR_EXPORT_BINARY
+	bool "Allow exporting the raw binary policy"
+	depends on SECURITY_APPARMOR_INTROSPECT_POLICY
+	select ZSTD_COMPRESS
+	select ZSTD_DECOMPRESS
+	default y
+	help
+	  This option allows reading back binary policy as it was loaded.
+	  It increases the amount of kernel memory needed by policy and
+	  also increases policy load time. This option is required for
+	  checkpoint and restore support, and debugging of loaded policy.
+
+config SECURITY_APPARMOR_PARANOID_LOAD
+	bool "Perform full verification of loaded policy"
+	depends on SECURITY_APPARMOR
+	default y
+	help
+	  This options allows controlling whether apparmor does a full
+	  verification of loaded policy. This should not be disabled
+	  except for embedded systems where the image is read only,
+	  includes policy, and has some form of integrity check.
+	  Disabling the check will speed up policy loads.
+
+config SECURITY_APPARMOR_KUNIT_TEST
+	tristate "Build KUnit tests for policy_unpack.c" if !KUNIT_ALL_TESTS
+	depends on KUNIT && SECURITY_APPARMOR
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the AppArmor KUnit tests.
+
+	  KUnit tests run during boot and output the results to the debug log
+	  in TAP format (https://testanything.org/). Only useful for kernel devs
+	  running KUnit test harness and are not for inclusion into a
+	  production build.
+
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.