[GWP-ASan] Provide runtime configuration through an env var + sysprop.
This patch introduces GWP-ASan system properties and environment
variables to control the internal sampling rates of GWP-ASan. This can
be used for:
1. "Torture testing" the system, i.e. running it under an extremely
high sampling rate under GWP-ASan.
2. Increasing sampling remotely to allow further crash report
collection of rare issues.
There are three sets of system properites:
1. libc.debug.gwp_asan.*.system_default: Default values for native
executables and system apps.
2. libc.debug.gwp_asan.*.app_default: Default values for non-system
apps, and
3. libc.debug.gwp_asan.*.<basename/app_name>: Default values for an
individual app or native process.
There are three variables that can be changed:
1. The allocation sampling rate (default: 2500) - using the environment
variable GWP_ASAN_SAMPLE_RATE or the libc.debug.gwp_asan.sample_rate.*
system property.
2. The process sampling rate (default: 128 for system apps/processes, 1
for opted-in apps) - using the environment variable
GWP_ASAN_PROCESS_SAMPLING or the libc.debug.gwp_asan.process_sampling.*
system property,
3. The number of slots available (default: 32) - using the environment
variable GWP_ASAN_MAX_ALLOCS or the libc.debug.gwp_asan.max_allocs.*
system property.
If not specified, #3 will be calculated as a ratio of the default
|2500 SampleRate : 32 slots|. So, a sample rate of "1250" (i.e. twice as
frequent sampling) will result in a doubling of the max_allocs to "64".
Bug: 219651032
Test: atest bionic-unit-tests
Change-Id: Idb40a2a4d074e01ce3c4e635ad639a91a32d570f
diff --git a/libc/bionic/sysprop_helpers.h b/libc/bionic/sysprop_helpers.h
new file mode 100644
index 0000000..a02c2dc
--- /dev/null
+++ b/libc/bionic/sysprop_helpers.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/cdefs.h>
+
+// Get the presiding config string, in the following order of priority:
+// 1. Environment variables.
+// 2. System properties, in the order they're specified in sys_prop_names.
+// If neither of these options are specified (or they're both an empty string),
+// this function returns false. Otherwise, it returns true, and the presiding
+// options string is written to the `options` buffer of size `size`. If this
+// function returns true, `options` is guaranteed to be null-terminated.
+// `options_size` should be at least PROP_VALUE_MAX.
+__LIBC_HIDDEN__ bool get_config_from_env_or_sysprops(const char* env_var_name,
+ const char* const* sys_prop_names,
+ size_t sys_prop_names_size, char* options,
+ size_t options_size);