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
Peter Collingbourne