perf_event: rules for system and simpleperf domain

This patch adds the necessary rules to support the existing usage of
perf_event_open by the system partition, which almost exclusively
concerns the simpleperf profiler. A new domain is introduced for some
(but not all) executions of the system image simpleperf. The following
configurations are supported:
* shell -> shell process (no domain transition)
* shell -> debuggable app (through shell -> runas -> runas_app)
* shell -> profileable app (through shell -> simpleperf_app_runner ->
                            untrusted_app -> simpleperf)
* debuggable/profile app -> self (through untrusted_app -> simpleperf)

simpleperf_app_runner still enters the untrusted_app domain immediately
before exec to properly inherit the categories related to MLS. My
understanding is that a direct transition would require modifying
external/selinux and seapp_contexts as with "fromRunAs", which seems
unnecessarily complex for this case.

runas_app can still run side-loaded binaries and use perf_event_open,
but it checks that the target app is exactly "debuggable"
(profileability is insufficient).

system-wide profiling is effectively constrained to "su" on debug
builds.

See go/perf-event-open-security for a more detailed explanation of the
scenarios covered here.

Tested: "atest CtsSimpleperfTestCases" on crosshatch-user/userdebug
Tested: manual simpleperf invocations on crosshatch-userdebug
Bug: 137092007
Change-Id: I2100929bae6d81f336f72eff4235fd5a78b94066

private/compat/29.0/29.0.ignore.cil

@@ -56,6 +56,7 @@
     ota_prop
     art_apex_dir
     service_manager_service
+    simpleperf
     soundtrigger_middleware_service
     sysfs_dm_verity
     system_group_file

private/file_contexts

@@ -338,6 +338,7 @@
 /system/bin/watchdogd            u:object_r:watchdogd_exec:s0
 /system/bin/apexd                u:object_r:apexd_exec:s0
 /system/bin/gsid                 u:object_r:gsid_exec:s0
+/system/bin/simpleperf           u:object_r:simpleperf_exec:s0
 /system/bin/simpleperf_app_runner    u:object_r:simpleperf_app_runner_exec:s0
 /system/bin/notify_traceur\.sh       u:object_r:notify_traceur_exec:s0
 /system/bin/migrate_legacy_obb_data\.sh u:object_r:migrate_legacy_obb_data_exec:s0

private/runas_app.te

@@ -16,3 +16,17 @@ r_dir_file(runas_app, untrusted_app_all)
 # Allow lldb/ndk-gdb/simpleperf to ptrace attach to debuggable app processes.
 allow runas_app untrusted_app_all:process { ptrace signal sigstop };
 allow runas_app untrusted_app_all:unix_stream_socket connectto;
+
+# Allow executing system image simpleperf without a domain transition.
+allow runas_app simpleperf_exec:file rx_file_perms;
+
+# Suppress denial logspam when simpleperf is trying to find a matching process
+# by scanning /proc/<pid>/cmdline files. The /proc/<pid> directories are within
+# the same domain as their respective process, most of which this domain is not
+# allowed to see.
+dontaudit runas_app domain:dir search;
+
+# Allow runas_app to call perf_event_open for profiling debuggable app
+# processes, but not the whole system.
+allow runas_app self:perf_event { open read write kernel };
+neverallow runas_app self:perf_event ~{ open read write kernel };

private/shell.te

@@ -83,3 +83,11 @@ allowxperm shell shell_data_file:dir ioctl {
   FS_IOC_GET_ENCRYPTION_POLICY
   FS_IOC_GET_ENCRYPTION_POLICY_EX
 };
+
+# Allow shell to execute simpleperf without a domain transition.
+allow shell simpleperf_exec:file rx_file_perms;
+
+# Allow shell to call perf_event_open for profiling other shell processes, but
+# not the whole system.
+allow shell self:perf_event { open read write kernel };
+neverallow shell self:perf_event ~{ open read write kernel };

private/simpleperf.te

@@ -0,0 +1,37 @@
+# Domain used when running /system/bin/simpleperf to profile a specific app.
+# Entered either by the app itself exec-ing the binary, or through
+# simpleperf_app_runner (with shell as its origin). Certain other domains
+# (runas_app, shell) can also exec this binary without a domain transition.
+typeattribute simpleperf coredomain;
+type simpleperf_exec, system_file_type, exec_type, file_type;
+
+domain_auto_trans({ untrusted_app_all -runas_app }, simpleperf_exec, simpleperf)
+
+# When running in this domain, simpleperf is scoped to profiling an individual
+# app. The necessary MAC permissions for profiling are more maintainable and
+# consistent if simpleperf is marked as an app domain as well (as, for example,
+# it will then see the same set of system libraries as the app).
+app_domain(simpleperf)
+untrusted_app_domain(simpleperf)
+
+# Allow ptrace attach to the target app, for reading JIT debug info (using
+# process_vm_readv) during unwinding and symbolization.
+allow simpleperf untrusted_app_all:process ptrace;
+
+# Allow using perf_event_open syscall for profiling the target app.
+allow simpleperf self:perf_event { open read write kernel };
+
+# Allow /proc/<pid> access for the target app (for example, when trying to
+# discover it by cmdline).
+r_dir_file(simpleperf, untrusted_app_all)
+
+# Suppress denial logspam when simpleperf is trying to find a matching process
+# by scanning /proc/<pid>/cmdline files. The /proc/<pid> directories are within
+# the same domain as their respective processes, most of which this domain is
+# not allowed to see.
+dontaudit simpleperf domain:dir search;
+
+# Neverallows:
+
+# Profiling must be confined to the scope of an individual app.
+neverallow simpleperf self:perf_event ~{ open read write kernel };

private/untrusted_app_all.te

@@ -168,3 +168,8 @@ userdebug_or_eng(`
   allow untrusted_app_all debugfs_kcov:file rw_file_perms;
   allowxperm untrusted_app_all debugfs_kcov:file ioctl { KCOV_INIT_TRACE KCOV_ENABLE KCOV_DISABLE };
 ')
+
+# Allow signalling simpleperf domain, which is the domain that the simpleperf
+# profiler runs as when executed by the app. The signals are used to control
+# the profiler (which would be profiling the app that is sending the signal).
+allow untrusted_app_all simpleperf:process signal;

public/domain.te

@@ -1173,10 +1173,11 @@ neverallow {
   -zygote
 } shell:process { transition dyntransition };
 
-# Only domains spawned from zygote, runas and simpleperf_app_runner may have the appdomain
-# attribute.
+# Only domains spawned from zygote, runas and simpleperf_app_runner may have
+# the appdomain attribute. simpleperf is excluded as a domain transitioned to
+# when running an app-scoped profiling session.
 neverallow { domain -simpleperf_app_runner -runas -app_zygote -webview_zygote -zygote } {
-  appdomain -shell userdebug_or_eng(`-su')
+  appdomain -shell -simpleperf userdebug_or_eng(`-su')
 }:process { transition dyntransition };
 
 # Minimize read access to shell- or app-writable symlinks.

public/simpleperf.te

@@ -0,0 +1 @@
+type simpleperf, domain;

public/su.te

@@ -52,6 +52,7 @@ userdebug_or_eng(`
   dontaudit su postinstall_file:filesystem *;
   dontaudit su domain:bpf *;
   dontaudit su unlabeled:vsock_socket *;
+  dontaudit su self:perf_event *;
 
   # VTS tests run in the permissive su domain on debug builds, but the HALs
   # being tested run in enforcing mode. Because hal_foo_server is enforcing

public/te_macros

@@ -171,16 +171,17 @@ typeattribute $1 appdomain;
 # Label tmpfs objects for all apps.
 type_transition $1 tmpfs:file appdomain_tmpfs;
 allow $1 appdomain_tmpfs:file { execute getattr map read write };
-neverallow { $1 -runas_app -shell } { domain -$1 }:file no_rw_file_perms;
-neverallow { appdomain -runas_app -shell -$1 } $1:file no_rw_file_perms;
+neverallow { $1 -runas_app -shell -simpleperf } { domain -$1 }:file no_rw_file_perms;
+neverallow { appdomain -runas_app -shell -simpleperf -$1 } $1:file no_rw_file_perms;
 # The Android security model guarantees the confidentiality and integrity
 # of application data and execution state. Ptrace bypasses those
-# confidentiality guarantees. Disallow ptrace access from system components
-# to apps. Crash_dump is excluded, as it needs ptrace access to
-# produce stack traces.  llkd is excluded, as it needs to inspect
-# the kernel stack for live lock conditions. runas_app is excluded, as it can
-# only access debuggable apps.
-neverallow { domain -$1 -crash_dump userdebug_or_eng(`-llkd') -runas_app } $1:process ptrace;
+# confidentiality guarantees. Disallow ptrace access from system components to
+# apps. crash_dump is excluded, as it needs ptrace access to produce stack
+# traces. runas_app is excluded, as it operates only on debuggable apps.
+# simpleperf is excluded, as it operates only on debuggable or profileable
+# apps. llkd is excluded, as it needs ptrace access to inspect stack traces for
+# live lock conditions.
+neverallow { domain -$1 -crash_dump userdebug_or_eng(`-llkd') -runas_app -simpleperf } $1:process ptrace;
 ')
 
 #####################################