commit e3e589829d16af9f7e73c7b70f74f3c5d5003e45

Author: Florian Weimer <fweimer@redhat.com>

Date:   Thu Dec 9 09:49:32 2021 +0100

    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>

diff --git a/manual/tunables.texi b/manual/tunables.texi

index 658547c6137bf177..1f5c410288eeecec 100644

--- a/manual/tunables.texi

+++ b/manual/tunables.texi

@@ -413,6 +413,16 @@ The value is measured in bytes.  The default is @samp{41943040}

 (fourty mibibytes).

 @end deftp

+@deftp Tunable glibc.pthread.rseq

+The @code{glibc.pthread.rseq} tunable can be set to @samp{0}, to disable

+restartable sequences support in @theglibc{}.  This enables applications

+to perform direct restartable sequence registration with the kernel.

+The default is @samp{1}, which means that @theglibc{} performs

+registration on behalf of the application.

+

+Restartable sequences are a Linux-specific extension.

+@end deftp

+

 @node Hardware Capability Tunables

 @section Hardware Capability Tunables

 @cindex hardware capability tunables

diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c

index d2b40924dafad316..f405fa356c2955ce 100644

--- a/nptl/pthread_create.c

+++ b/nptl/pthread_create.c

@@ -369,7 +369,10 @@ start_thread (void *arg)

   __ctype_init ();

   /* Register rseq TLS to the kernel.  */

-  rseq_register_current_thread (pd);

+  {

+    bool do_rseq = THREAD_GETMEM (pd, flags) & ATTR_FLAG_DO_RSEQ;

+    rseq_register_current_thread (pd, do_rseq);

+  }

 #ifndef __ASSUME_SET_ROBUST_LIST

   if (__nptl_set_robust_list_avail)

@@ -678,6 +681,11 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,

   pd->flags = ((iattr->flags & ~(ATTR_FLAG_SCHED_SET | ATTR_FLAG_POLICY_SET))

 	       | (self->flags & (ATTR_FLAG_SCHED_SET | ATTR_FLAG_POLICY_SET)));

+  /* Inherit rseq registration state.  Without seccomp filters, rseq

+     registration will either always fail or always succeed.  */

+  if ((int) THREAD_GETMEM_VOLATILE (self, rseq_area.cpu_id) >= 0)

+    pd->flags |= ATTR_FLAG_DO_RSEQ;

+

   /* Initialize the field for the ID of the thread which is waiting

      for us.  This is a self-reference in case the thread is created

      detached.  */

diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c

index fedb876fdb2642d2..b39dfbff2c6678d5 100644

--- a/sysdeps/nptl/dl-tls_init_tp.c

+++ b/sysdeps/nptl/dl-tls_init_tp.c

@@ -23,6 +23,9 @@

 #include <tls.h>

 #include <rseq-internal.h>

+#define TUNABLE_NAMESPACE pthread

+#include <dl-tunables.h>

+

 #ifndef __ASSUME_SET_ROBUST_LIST

 bool __nptl_set_robust_list_avail;

 rtld_hidden_data_def (__nptl_set_robust_list_avail)

@@ -92,7 +95,13 @@ __tls_init_tp (void)

       }

   }

-  rseq_register_current_thread (pd);

+  {

+    bool do_rseq = true;

+#if HAVE_TUNABLES

+    do_rseq = TUNABLE_GET (rseq, int, NULL);

+#endif

+    rseq_register_current_thread (pd, do_rseq);

+  }

   /* Set initial thread's stack block from 0 up to __libc_stack_end.

      It will be bigger than it actually is, but for unwind.c/pt-longjmp.c

diff --git a/sysdeps/nptl/dl-tunables.list b/sysdeps/nptl/dl-tunables.list

index ac5d053298725468..d24f4be0d08ba407 100644

--- a/sysdeps/nptl/dl-tunables.list

+++ b/sysdeps/nptl/dl-tunables.list

@@ -27,5 +27,11 @@ glibc {

       type: SIZE_T

       default: 41943040

     }

+    rseq {

+      type: INT_32

+      minval: 0

+      maxval: 1

+      default: 1

+    }

   }

 }

diff --git a/sysdeps/nptl/internaltypes.h b/sysdeps/nptl/internaltypes.h

index 50a2ad19ae7210ae..8205c6d15a918952 100644

--- a/sysdeps/nptl/internaltypes.h

+++ b/sysdeps/nptl/internaltypes.h

@@ -49,6 +49,7 @@ struct pthread_attr

 #define ATTR_FLAG_OLDATTR		0x0010

 #define ATTR_FLAG_SCHED_SET		0x0020

 #define ATTR_FLAG_POLICY_SET		0x0040

+#define ATTR_FLAG_DO_RSEQ		0x0080

 /* Used to allocate a pthread_attr_t object which is also accessed

    internally.  */

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile

index f84ccd6bbb3b16ad..d30d21898b402d1e 100644

--- a/sysdeps/unix/sysv/linux/Makefile

+++ b/sysdeps/unix/sysv/linux/Makefile

@@ -135,6 +135,12 @@ 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 \

@@ -226,6 +232,8 @@ $(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 909f5478251d3d13..15bc7ffd6eda632d 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 0000000000000000..000e351872fc2f76

--- /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>