llkd: Add stack symbol checking
Feature outlined here is only available on userdebug or eng builds.
Blocked for security reasons because requires ptrace capabilities.
Add ro.llk.stack to list a set of symbols that should rarely happen
but if persistent in multiple checks, indicates a live lock condition.
At ro.llk.stack.timeout_ms the process is sent a kill, if it remains,
then panic the kernel.
There is no ABA detection in the paths, the condition for the
stack symbol being present instantaneously must be its rarity of
being caught. If a livelock occurs in the path of the symbol, then
it is possible more than one path could be stuck in the state, but
the best candidate symbols are found underneath a lock resulting in
only one process being the culprit, and the best aim. There may be
processes that induce a look of persistence, if so the symbol is not
a candidate for checking.
Add ro.llk.blacklist.process.stack to list process names we want
to skip checking. This configuration parameter is also used to
prevent sepolicy noise when trying to acquire stacks from non
ptrace'able services.
Test: gTest llkd_unit_tests
Bug: 33808187
Bug: 111910505
Bug: 80502612
Change-Id: Ie71221e371b189bbdda2a1155d47826997842dcc
diff --git a/llkd/include/llkd.h b/llkd/include/llkd.h
index e3ae4bb..d0188ec 100644
--- a/llkd/include/llkd.h
+++ b/llkd/include/llkd.h
@@ -43,9 +43,12 @@
#define KHT_TIMEOUT_PROPERTY "ro.khungtask.timeout"
#define LLK_D_TIMEOUT_MS_PROPERTY "ro.llk.D.timeout_ms"
#define LLK_Z_TIMEOUT_MS_PROPERTY "ro.llk.Z.timeout_ms"
+#define LLK_STACK_TIMEOUT_MS_PROPERTY "ro.llk.stack.timeout_ms"
#define LLK_CHECK_MS_PROPERTY "ro.llk.check_ms"
/* LLK_CHECK_MS_DEFAULT = actual timeout_ms / LLK_CHECKS_PER_TIMEOUT_DEFAULT */
#define LLK_CHECKS_PER_TIMEOUT_DEFAULT 5
+#define LLK_CHECK_STACK_PROPERTY "ro.llk.stack"
+#define LLK_CHECK_STACK_DEFAULT ""
#define LLK_BLACKLIST_PROCESS_PROPERTY "ro.llk.blacklist.process"
#define LLK_BLACKLIST_PROCESS_DEFAULT \
"0,1,2,init,[kthreadd],[khungtaskd],lmkd,lmkd.llkd,llkd,watchdogd,[watchdogd],[watchdogd/0]"
@@ -53,6 +56,8 @@
#define LLK_BLACKLIST_PARENT_DEFAULT "0,2,[kthreadd]"
#define LLK_BLACKLIST_UID_PROPERTY "ro.llk.blacklist.uid"
#define LLK_BLACKLIST_UID_DEFAULT ""
+#define LLK_BLACKLIST_STACK_PROPERTY "ro.llk.blacklist.process.stack"
+#define LLK_BLACKLIST_STACK_DEFAULT "init,lmkd.llkd,llkd,keystore,/system/bin/keystore"
/* clang-format on */
__END_DECLS