[GWP-ASan] [heapprofd] Use ephemeral dispatch table when death prof.
GWP-ASan + heapprofd don't currently play nice together in some
circumstances. heapprofd thinks it's still an only child, and refuses to
accept the existence of its little brother, GWP-ASan.
If GWP-ASan is installed before heapprofd, then heapprofd is *required*
to respect that libc has a favourite child. If an allocation/free is passed
to heapprofd, then heapprofd *must* (eventually) pass that allocation/free to
GWP-ASan. If heapprofd doesn't do this, then a free() of a GWP-ASan
allocation can be passed to the system allocator.
This can happen in two places right now:
1. The heapprofd hooks simply clobber any trace of what was
previously in the default_dispatch_table when enabled through the
heapprofd signal.
2. Heapprofd can die when the system is under significant pressure.
Some pipes can timeout, which ends up in the client calling ShutdownLazy()
-> mallopt(M_RESET_HOOKS) -> DispatchReset(). This also clobbers any
trace of the previous default_dispatch_table.
To fix both these problems, we fix heapprofd to restore the previous
default_dispatch_table whenever either circumstance happens. We do some
tricky copying to avoid race conditions on the malloc_dispatch_table in
fixing #1.
Bug: 135634846
Test: Run HeapprofdEndToEnd.NativeProfilingActiveAtProcessExit/ForkMode
a significant number of times with large amounts of system pressure (I
just run bionic-unit-tests-scudo in parallel). You will see some test
failures where heapprofd died due to system pressure, but never a death
from the allocator. Tests should never fail when the system isn't under
immense pressure.
Change-Id: I20ab340d4bdc35d6d1012da5ee1a25634428d097
diff --git a/libc/bionic/gwp_asan_wrappers.h b/libc/bionic/gwp_asan_wrappers.h
index fd9c547..a39d50b 100644
--- a/libc/bionic/gwp_asan_wrappers.h
+++ b/libc/bionic/gwp_asan_wrappers.h
@@ -37,3 +37,8 @@
// Maybe initialize GWP-ASan. Set force_init to true to bypass process sampling.
bool MaybeInitGwpAsan(libc_globals* globals, bool force_init = false);
+
+// Returns whether GWP-ASan is the provided dispatch table pointer. Used in
+// heapprofd's signal-initialization sequence to determine the intermediate
+// dispatch pointer to use when initing.
+bool DispatchIsGwpAsan(const MallocDispatch* dispatch);