nptl: Add glibc.pthread.rseq tunable to control rseq registration

This tunable allows applications to register the rseq area instead
of glibc.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

3 files changed, 109 insertions, 7 deletions

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index eb0f5fc021..62a796f214 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -136,6 +136,12 @@ tests-internal += \
   tst-sigcontext-get_pc \
   # tests-internal
 
+ifneq (no,$(have-tunables))
+tests-internal += \
+  tst-rseq-disable \
+  # tests-internal $(have-tunables)
+endif
+
 tests-time64 += \
   tst-adjtimex-time64 \
   tst-clock_adjtime-time64 \
@@ -227,6 +233,8 @@ $(objpfx)tst-mman-consts.out: ../sysdeps/unix/sysv/linux/tst-mman-consts.py
 	  < /dev/null > $@ 2>&1; $(evaluate-test)
 $(objpfx)tst-mman-consts.out: $(sysdeps-linux-python-deps)
 
+tst-rseq-disable-ENV = GLIBC_TUNABLES=glibc.pthread.rseq=0
+
 endif # $(subdir) == misc
 
 ifeq ($(subdir),time)
diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
index 909f547825..15bc7ffd6e 100644
--- a/sysdeps/unix/sysv/linux/rseq-internal.h
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -21,22 +21,27 @@
 #include <sysdep.h>
 #include <errno.h>
 #include <kernel-features.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <sys/rseq.h>
 
 #ifdef RSEQ_SIG
 static inline void
-rseq_register_current_thread (struct pthread *self)
+rseq_register_current_thread (struct pthread *self, bool do_rseq)
 {
-  int ret = INTERNAL_SYSCALL_CALL (rseq,
-                                   &self->rseq_area, sizeof (self->rseq_area),
-                                   0, RSEQ_SIG);
-  if (INTERNAL_SYSCALL_ERROR_P (ret))
-    THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+  if (do_rseq)
+    {
+      int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
+                                       sizeof (self->rseq_area),
+                                       0, RSEQ_SIG);
+      if (!INTERNAL_SYSCALL_ERROR_P (ret))
+        return;
+    }
+  THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
 }
 #else /* RSEQ_SIG */
 static inline void
-rseq_register_current_thread (struct pthread *self)
+rseq_register_current_thread (struct pthread *self, bool do_rseq)
 {
   THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
 }
diff --git a/sysdeps/unix/sysv/linux/tst-rseq-disable.c b/sysdeps/unix/sysv/linux/tst-rseq-disable.c
new file mode 100644
index 0000000000..000e351872
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/tst-rseq-disable.c
@@ -0,0 +1,89 @@
+/* Test disabling of rseq registration via tunable.
+   Copyright (C) 2021 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/>.  */
+
+#include <errno.h>
+#include <stdio.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/xthread.h>
+#include <sysdep.h>
+#include <unistd.h>
+
+#ifdef RSEQ_SIG
+
+/* Check that rseq can be registered and has not been taken by glibc.  */
+static void
+check_rseq_disabled (void)
+{
+  struct pthread *pd = THREAD_SELF;
+  TEST_COMPARE ((int) pd->rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+
+  int ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
+                     0, RSEQ_SIG);
+  if (ret == 0)
+    {
+      ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
+                     RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+      TEST_COMPARE (ret, 0);
+      pd->rseq_area.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+    }
+  else
+    {
+      TEST_VERIFY (errno != -EINVAL);
+      TEST_VERIFY (errno != -EBUSY);
+    }
+}
+
+static void *
+thread_func (void *ignored)
+{
+  check_rseq_disabled ();
+  return NULL;
+}
+
+static void
+proc_func (void *ignored)
+{
+  check_rseq_disabled ();
+}
+
+static int
+do_test (void)
+{
+  puts ("info: checking main thread");
+  check_rseq_disabled ();
+
+  puts ("info: checking main thread (2)");
+  check_rseq_disabled ();
+
+  puts ("info: checking new thread");
+  xpthread_join (xpthread_create (NULL, thread_func, NULL));
+
+  puts ("info: checking subprocess");
+  support_isolate_in_subprocess (proc_func, NULL);
+
+  return 0;
+}
+#else /* !RSEQ_SIG */
+static int
+do_test (void)
+{
+  FAIL_UNSUPPORTED ("glibc does not define RSEQ_SIG, skipping test");
+}
+#endif
+
+#include <support/test-driver.c>