Re: [PATCH] elf: Add __libc_get_static_tls_bounds [BZ #16291]

[Florian Weimer <fweimer@redhat.com>]

* Fangrui Song:

> Sanitizer runtimes need static TLS boundaries for a variety of use cases.
>
> * asan/hwasan/msan/tsan need to unpoison static TLS blocks to prevent false
>   positives due to reusing the TLS blocks with a previous thread.
> * lsan needs TCB for pointers into pthread_setspecific regions.
>
> See https://maskray.me/blog/2021-02-14-all-about-thread-local-storage
> for details.
>
> compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp GetTls has
> to infer the static TLS bounds from TP, _dl_get_tls_static_info, and
> hard-coded TCB sizes. Currently this is somewhat robust for
> aarch64/powerpc64/x86-64 but is brittle for many other architectures.
>
> This patch implements __libc_get_static_tls_bounds@@GLIBC_PRIVATE which
> is available in Android bionic since API level 31. This API allows the
> sanitizer code to be more robust. _dl_get_tls_static_info@@GLIBC_PRIVATE
> can probably be removed when Clang/GCC sanitizers drop reliance on it.
> I am unclear whether the version should be GLIBC_2.*.

Does this really cover the right memory region?  I assume LSAN needs
something that identifies pointers to malloc'ed memory that are stored
in non-malloc'ed (mmap'ed) memory.  The static TLS region is certainly a
place where such pointers can be stored.  But struct pthread also
contains other such pointers: the DTV, the TPP data, and POSIX TLS
(pthread_setspecific) data, and struct pthread is not obviously part of
the static TLS region.

Thanks,
Florian