With memtag_stack, each function is responsible for cleaning up
allocation tags for its stack frame. Allocation tags for anything below
SP must match the address tag in SP.
Both vfork and longjmp implement non-local control transfer which
abandons part of the stack without proper cleanup. Update allocation
tags:
* For longjmp, we know both source and destination values of SP.
* For vfork, save the value of SP before exit() or exec*() - the only
valid ways of ending the child process according to POSIX - and reset
tags from there to SP-in-parent.
This is not 100% solid and can be confused by a number of hopefully
uncommon conditions:
* Segmented stacks.
* Longjmp from sigaltstack into the main stack.
* Some kind of userspace thread implementation using longjmp (that's UB,
longjmp can only return to the caller on the current stack).
* and other strange things.
This change adds a sanity limit on the size of the tag cleanup. Also,
this logic is only activated in the binaries that carry the
NT_MEMTAG_STACK note (set by -fsanitize=memtag-stack) which is meant as
a debugging configuration, is not compatible with pre-armv9 CPUs, and
should not be set on production code.
Bug: b/174878242
Test: fvp_mini with ToT LLVM (more test in a separate change)
Change-Id: Ibef8b2fc5a6ce85c8e562dead1019964d9f6b80b
The first time should_trace() returns true, bionic_trace_begin() calls
open() on trace_marker.
The problem is that open() can call bionic_trace_begin(). We've observed
this happening, for example when:
* fdtrack is enabled. dlopen("libfdtrack.so") can be used to enable
fdtrack on a process.
* ThreadA is busy unwinding inside fdtrack and is holding an fdtrack
internal mutex.
* ThreadB calls bionic_trace_begin() for the first time since the
property "debug.atrace.tags.enableflags" contains ATRACE_TAG_BIONIC.
* ThreadB calls open("/sys/kernel/tracing/trace_marker"). Since fdtrack
is enabled, ThreadB tries to do unwinding as well.
* ThreadB, inside fdtrack's unwinding tries to grab the same mutex that
ThreadA is holding.
* Mutex contention is reported using bionic_systrace, therefore
bionic_trace_begin() is called again on ThreadB.
* ThreadB tries to grab g_lock in bionin_systrace.cpp, but that's
already held by ThreadB itself, earlier on the stack. Therefore
ThreadB is stuck.
I managed to reproduce the above scenario by manually pausing ThreadA
inside unwinding with a debugger and letting ThreadB hitting
bionic_trace_begin() for the first time.
We could avoid using g_lock while calling open() (either by releasing
g_lock and reacquiring it later, or by using atomics), but
bionic_trace_begin() would try to call open() again. In my tests, open()
does not call bionic_trace_begin() a third time, because fdtrack has
reentrancy protection, but there might be another code path inside open
that calls bionic_trace_begin again (it could be racy or only happen in
certain configurations).
This commit fixes the problem by implementing reentrancy protection in
bionic_systrace.
Sample callstack from ThreadA deadlocked before the fix:
```
* frame #0: 0x0000007436db077c libc.so`syscall at syscall.S:41
frame #1: 0x0000007436db0ba0 libc.so`bionic_trace_begin(char const*) [inlined] __futex(ftx=0x000000743737a548, op=<unavailable>, value=2, timeout=0x0000000000000000, bitset=-1) at bionic_futex.h:45:16
frame #2: 0x0000007436db0b8c libc.so`bionic_trace_begin(char const*) [inlined] __futex_wait_ex(ftx=0x000000743737a548, value=2) at bionic_futex.h:66:10
frame #3: 0x0000007436db0b78 libc.so`bionic_trace_begin(char const*) [inlined] Lock::lock(this=0x000000743737a548) at bionic_lock.h:67:7
frame #4: 0x0000007436db0b74 libc.so`bionic_trace_begin(char const*) [inlined] should_trace() at bionic_systrace.cpp:38:10
frame #5: 0x0000007436db0b74 libc.so`bionic_trace_begin(message="Contending for pthread mutex") at bionic_systrace.cpp:59:8
frame #6: 0x0000007436e193e4 libc.so`NonPI::MutexLockWithTimeout(pthread_mutex_internal_t*, bool, timespec const*) [inlined] NonPI::NormalMutexLock(mutex=0x0000007296cae9f0, shared=0, use_realtime_clock=false, abs_timeout_or_null=0x0000000000000000) at pthread_mutex.cpp:592:17
frame #7: 0x0000007436e193c8 libc.so`NonPI::MutexLockWithTimeout(mutex=0x0000007296cae9f0, use_realtime_clock=false, abs_timeout_or_null=0x0000000000000000) at pthread_mutex.cpp:719:16
frame #8: 0x0000007436e1912c libc.so`::pthread_mutex_lock(mutex_interface=<unavailable>) at pthread_mutex.cpp:839:12 [artificial]
frame #9: 0x00000071a4e5b290 libfdtrack.so`std::__1::mutex::lock() [inlined] std::__1::__libcpp_mutex_lock(__m=<unavailable>) at __threading_support:256:10
frame #10: 0x00000071a4e5b28c libfdtrack.so`std::__1::mutex::lock(this=<unavailable>) at mutex.cpp:31:14
frame #11: 0x00000071a4e32634 libfdtrack.so`unwindstack::Elf::Step(unsigned long, unwindstack::Regs*, unwindstack::Memory*, bool*, bool*) [inlined] std::__1::lock_guard<std::__1::mutex>::lock_guard(__m=0x0000007296cae9f0) at __mutex_base:104:27
frame #12: 0x00000071a4e32618 libfdtrack.so`unwindstack::Elf::Step(this=0x0000007296cae9c0, rel_pc=66116, regs=0x0000007266ca0470, process_memory=0x0000007246caa130, finished=0x0000007ff910efb4, is_signal_frame=0x0000007ff910efb0) at Elf.cpp:206:31
frame #13: 0x00000071a4e2b3b0 libfdtrack.so`unwindstack::LocalUnwinder::Unwind(this=0x00000071a4ea1528, frame_info=<unavailable>, max_frames=34) at LocalUnwinder.cpp:102:22
frame #14: 0x00000071a4e2a3ec libfdtrack.so`fd_hook(event=<unavailable>) at fdtrack.cpp:119:18
frame #15: 0x0000007436dbf684 libc.so`::__open_2(pathname=<unavailable>, flags=<unavailable>) at open.cpp:72:10
frame #16: 0x0000007436db0a04 libc.so`bionic_trace_begin(char const*) [inlined] open(pathname=<unavailable>, flags=524289) at fcntl.h:63:12
frame #17: 0x0000007436db09f0 libc.so`bionic_trace_begin(char const*) [inlined] get_trace_marker_fd() at bionic_systrace.cpp:49:25
frame #18: 0x0000007436db09c0 libc.so`bionic_trace_begin(message="pthread_create") at bionic_systrace.cpp:63:25
```
Bug: 213642769
Change-Id: I10d331859045cb4a8609b007f5c6cf2577ff44df
Introduce an android_mallopt(M_DISABLE_MEMORY_MITIGATIONS) API call
that may be used to disable zero- or pattern-init on non-MTE hardware,
or memory tagging on MTE hardware. The intent is that this function
may be called at any time, including when there are multiple threads
running.
Disabling zero- or pattern-init is quite trivial, we just need to set
a global variable to 0 via a Scudo API call (although there will be
some separate work required on the Scudo side to make this operation
thread-safe).
It is a bit more tricky to disable MTE across a process, because
the kernel does not provide an API for disabling tag checking in all
threads in a process, only per-thread. We need to send a signal to each
of the process's threads with a handler that issues the required prctl
call, and lock thread creation for the duration of the API call to
avoid races between thread enumeration and calls to pthread_create().
Bug: 135772972
Change-Id: I81ece86ace916eb6b435ab516cd431ec4b48a3bf
A downstream user of bionic has a test that requires the sizes and
offsets of various fields in pthread_internal_t to be consistent
between x86 and arm32, and between x86_64 and arm64, by checking that
the sizes and offsets match hardcoded constants. Since this test often
makes it difficult to update bionic's internal data structures, add
a test to bionic that does the same thing so that we can remove the
downstream test and make it easier to change internal data structures
in bionic.
Change-Id: Id5bd3f9fae00aa3b50d1b1267e782e26fe6c8369
