[PATCH v7 0/4] rseq: Make rseq work with protection keys

[Dmitry Vyukov <dvyukov@google.com>]

If an application registers rseq, and ever switches to another pkey
protection (such that the rseq becomes inaccessible), then any
context switch will cause failure in __rseq_handle_notify_resume()
attempting to read/write struct rseq and/or rseq_cs. Since context
switches are asynchronous and are outside of the application control
(not part of the restricted code scope), temporarily enable access
to 0 (default) PKEY to read/write rseq/rseq_cs.
0 is the only PKEY supported for rseq for now.
Theoretically other PKEYs can be supported, but it's unclear
how/if that can work. So for now we don't support that to simplify
code.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org

Dmitry Vyukov (4):
  pkeys: add API to switch to permissive/zero pkey register
  x86/signal: Use write_permissive_pkey_val() helper
  rseq: Make rseq work with protection keys
  selftests/rseq: Add test for rseq+pkeys

 arch/x86/Kconfig                         |   1 +
 arch/x86/include/asm/pkeys.h             |  30 +++++++
 arch/x86/include/asm/pkru.h              |  10 ++-
 arch/x86/kernel/signal.c                 |   6 +-
 include/linux/pkeys.h                    |  31 +++++++
 include/uapi/linux/rseq.h                |   4 +
 kernel/rseq.c                            |  11 +++
 mm/Kconfig                               |   2 +
 tools/testing/selftests/rseq/Makefile    |   2 +-
 tools/testing/selftests/rseq/pkey_test.c | 101 +++++++++++++++++++++++
 tools/testing/selftests/rseq/rseq.h      |   1 +
 11 files changed, 191 insertions(+), 8 deletions(-)
 create mode 100644 tools/testing/selftests/rseq/pkey_test.c


base-commit: 4a95bc121ccdaee04c4d72f84dbfa6b880a514b6
-- 
2.49.0.1143.g0be31eac6b-goog