Linux: Perform rseq registration at C startup and thread creation

Register rseq TLS for each thread (including main), and unregister for
each thread (excluding main).  "rseq" stands for Restartable Sequences.

See the rseq(2) man page proposed here:
  https://lkml.org/lkml/2018/9/19/647

Those are based on glibc master branch commit 3ee1e0ec5c.
The rseq system call was merged into Linux 4.18.

The TLS_STATIC_SURPLUS define is increased to leave additional room for
dlopen'd initial-exec TLS, which keeps elf/tst-auditmany working.

The increase (76 bytes) is larger than 32 bytes because it has not been
increased in quite a while.  The cost in terms of additional TLS storage
is quite significant, but it will also obscure some initial-exec-related
dlopen failures.

1 files changed, 73 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
new file mode 100644
index 0000000000..8f6772ca1d
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -0,0 +1,73 @@
+/* Restartable Sequences internal API.  Linux implementation.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef RSEQ_INTERNAL_H
+#define RSEQ_INTERNAL_H
+
+#include <sysdep.h>
+#include <errno.h>
+#include <kernel-features.h>
+#include <stdio.h>
+#include <sys/rseq.h>
+
+#ifdef RSEQ_SIG
+static inline void
+rseq_register_current_thread (void)
+{
+  int ret;
+
+  if (__rseq_abi.cpu_id != RSEQ_CPU_ID_UNINITIALIZED)
+    __libc_fatal ("glibc fatal error: "
+                  "rseq already initialized for this thread\n");
+  ret = INTERNAL_SYSCALL_CALL (rseq, &__rseq_abi, sizeof (struct rseq),
+                               0, RSEQ_SIG);
+  if (INTERNAL_SYSCALL_ERROR_P (ret))
+    {
+      const char *msg = NULL;
+
+      switch (INTERNAL_SYSCALL_ERRNO (ret))
+        {
+        case ENOSYS:    /* rseq system call not implemented.  */
+        case EPERM:     /* rseq system call filtered by seccomp.  */
+        case EACCES:    /* rseq system call filtered by seccomp.  */
+          __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+          break;
+        case EBUSY:
+          msg = "glibc fatal error: rseq already registered for this thread\n";
+          break;
+        case EFAULT:
+          msg = "glibc fatal error: rseq parameter is an invalid address\n";
+          break;
+        case EINVAL:
+          msg = "glibc fatal error: rseq parameters are invalid\n";
+          break;
+        default:
+          msg = "glibc fatal error: unexpected rseq errno\n";
+          break;
+        }
+      if (msg != NULL)
+        __libc_fatal (msg);
+    }
+}
+#else /* RSEQ_SIG */
+static inline void
+rseq_register_current_thread (void)
+{
+}
+#endif /* RSEQ_SIG */
+
+#endif /* rseq-internal.h */