[PATCH v2 0/4] aarch64: Support enforcing BTI

[Yury Khrustalev]

Current behaviour on AArch64 targets that support Branch Target
Authentication (BTI) allows to load a dependency that is not
BTI-marked (via appropriate ELF property). It is useful to support
behaviour when loading dependencies with and without BTI marking
in the same process results in an error. To do this, we add new
Glibc tunable glibc.cpu.aarch64_bti.

The default value 0 of this tunable corresponds to existing behaviour
and we lable this value as "permissive". To enforce BTI protection,
the process might be started with value 1 of this tunable. In this
case all the dependencies loaded by the dynamic loader will have to
be correctly marked and, if a module is loaded via dlopen, an error
will be returned from this function.

To facilitate testing, we need to add new configure checks.

---

Passes regression in AArch64. OK for trunk?
Base commit: 40a751b004

---

Changes in v2:
 - Fixed several things based on upstream feedback.
 - Added new configure check for a macro defined by a compiler
   to check if BTI branch protection was enabled.
 - v1: https://inbox.sourceware.org/libc-alpha/20251031153704.3883875-1-yury.khrustalev@arm.com/

---

Yury Khrustalev (4):
  aarch64: add configure checks for BTI support
  aarch64: Add glibc.cpu.aarch64_bti tunable
  aarch64: Support enforcing BTI on dependencies
  aarch64: add tests for glibc.cpu.aarch64_bti behaviour

 aclocal.m4                                    |  14 ++
 configure                                     | 126 ++++++++++++++++++
 configure.ac                                  |  27 ++++
 manual/tunables.texi                          |  16 +++
 sysdeps/aarch64/Makefile                      |  58 +++++++-
 sysdeps/aarch64/cpu-features.h                |   5 +
 sysdeps/aarch64/dl-bti.c                      |  16 ++-
 sysdeps/aarch64/dl-tunables.list              |   6 +
 sysdeps/aarch64/linkmap.h                     |   1 +
 sysdeps/aarch64/tst-bti-abort-imm.c           |   3 +
 sysdeps/aarch64/tst-bti-abort-transitive.c    |   3 +
 sysdeps/aarch64/tst-bti-abort-unprot.c        |   3 +
 sysdeps/aarch64/tst-bti-abort.sh              |  39 ++++++
 sysdeps/aarch64/tst-bti-dep-prot.c            |   3 +
 sysdeps/aarch64/tst-bti-dlopen-imm.c          |   6 +
 sysdeps/aarch64/tst-bti-dlopen-prot.c         |   6 +
 sysdeps/aarch64/tst-bti-dlopen-transitive.c   |   6 +
 sysdeps/aarch64/tst-bti-mod-prot.c            |   2 +
 sysdeps/aarch64/tst-bti-mod-unprot.c          |   2 +
 sysdeps/aarch64/tst-bti-mod.c                 |  25 ++++
 sysdeps/aarch64/tst-bti-permissive-dlopen.c   |   6 +
 sysdeps/aarch64/tst-bti-permissive-imm.c      |   3 +
 .../aarch64/tst-bti-permissive-transitive.c   |   3 +
 sysdeps/aarch64/tst-bti-skeleton-dlopen.c     |  62 +++++++++
 sysdeps/aarch64/tst-bti-skeleton.c            |  45 +++++++
 .../unix/sysv/linux/aarch64/cpu-features.c    |   2 +
 sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c |  16 +++
 27 files changed, 502 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/aarch64/tst-bti-abort-imm.c
 create mode 100644 sysdeps/aarch64/tst-bti-abort-transitive.c
 create mode 100644 sysdeps/aarch64/tst-bti-abort-unprot.c
 create mode 100644 sysdeps/aarch64/tst-bti-abort.sh
 create mode 100644 sysdeps/aarch64/tst-bti-dep-prot.c
 create mode 100644 sysdeps/aarch64/tst-bti-dlopen-imm.c
 create mode 100644 sysdeps/aarch64/tst-bti-dlopen-prot.c
 create mode 100644 sysdeps/aarch64/tst-bti-dlopen-transitive.c
 create mode 100644 sysdeps/aarch64/tst-bti-mod-prot.c
 create mode 100644 sysdeps/aarch64/tst-bti-mod-unprot.c
 create mode 100644 sysdeps/aarch64/tst-bti-mod.c
 create mode 100644 sysdeps/aarch64/tst-bti-permissive-dlopen.c
 create mode 100644 sysdeps/aarch64/tst-bti-permissive-imm.c
 create mode 100644 sysdeps/aarch64/tst-bti-permissive-transitive.c
 create mode 100644 sysdeps/aarch64/tst-bti-skeleton-dlopen.c
 create mode 100644 sysdeps/aarch64/tst-bti-skeleton.c

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2.47.3