[RFC PATCH 1/2] glibc: Perform rseq(2) registration at nptl init and thread creation (v3)

Mathieu Desnoyers
2018-11-02T11:53:16Z

Here is a third round of prototype registering rseq(2) TLS for each
thread (including main), and unregistering for each thread (excluding
main). "rseq" stands for Restartable Sequences.

Remaining open questions:

- How early do we want to register rseq and how late do we want to
unregister it ? It's important to consider if we expect rseq to
be used by the memory allocator and within destructor callbacks.
However, we want to be sure the TLS (__thread) area is properly
allocated across its entire use by rseq.

- We do not need an atomic increment/decrement for the refcount per
se. Just being atomic with respect to the current thread (and nested
signals) would be enough. What is the proper API to use there ?

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

This patch is based on glibc 2.28.

To try it out, refer to the following kernel and librseq development
branches:

* rseq and cpu_opv:
https://github.com/compudj/linux-percpu-dev branch: rseq/dev-local

* librseq:
https://github.com/compudj/librseq branch: master

TODO:

- Add documentation, tests and a NEWS entry.
- Update ABI test baselines.
- Update abilist for non-x86-64 architectures.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Carlos O'Donell <carlos@redhat.com>
CC: Florian Weimer <fweimer@redhat.com>
CC: Joseph Myers <joseph@codesourcery.com>
CC: Szabolcs Nagy <szabolcs.nagy@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ben Maurer <bmaurer@fb.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Dave Watson <davejwatson@fb.com>
CC: Paul Turner <pjt@google.com>
CC: libc-alpha@sourceware.org
CC: linux-kernel@vger.kernel.org
CC: linux-api@vger.kernel.org
---
Changes since v1:
- Move __rseq_refcount to an extra field at the end of __rseq_abi to
eliminate one symbol.

All libraries/programs which try to register rseq (glibc,
early-adopter applications, early-adopter libraries) should use the
rseq refcount. It becomes part of the ABI within a user-space
process, but it's not part of the ABI shared with the kernel per se.

- Restructure how this code is organized so glibc keeps building on
non-Linux targets.

- Use non-weak symbol for __rseq_abi.

- Move rseq registration/unregistration implementation into its own
nptl/rseq.c compile unit.

- Move __rseq_abi symbol under GLIBC_2.29.

Changes since v2:
- Move __rseq_refcount to its own symbol, which is less ugly than
trying to play tricks with the rseq uapi.
- Move __rseq_abi from nptl to csu (C start up), so it can be used
across glibc, including memory allocator and sched_getcpu(). The
__rseq_refcount symbol is kept in nptl, because there is no reason
to use it elsewhere in glibc.
---
csu/Makefile | 2 +-
csu/Versions | 3 +
csu/rseq.c | 38 ++++++++++
nptl/Makefile | 2 +-
nptl/Versions | 4 ++
nptl/nptl-init.c | 3 +
nptl/pthreadP.h | 3 +
nptl/pthread_create.c | 8 +++
nptl/rseq.c | 42 +++++++++++
sysdeps/nptl/rseq-internal.h | 34 +++++++++
sysdeps/unix/sysv/linux/rseq-internal.h | 72 +++++++++++++++++++
.../unix/sysv/linux/x86_64/64/libc.abilist | 1 +
.../sysv/linux/x86_64/64/libpthread.abilist | 1 +
13 files changed, 211 insertions(+), 2 deletions(-)
create mode 100644 csu/rseq.c
create mode 100644 nptl/rseq.c
create mode 100644 sysdeps/nptl/rseq-internal.h
create mode 100644 sysdeps/unix/sysv/linux/rseq-internal.h

diff --git a/csu/Makefile b/csu/Makefile
index 88fc77662e..81d471587f 100644
--- a/csu/Makefile
+++ b/csu/Makefile
@@ -28,7 +28,7 @@ include ../Makeconfig

routines = init-first libc-start $(libc-init) sysdep version check_fds \
libc-tls elf-init dso_handle
-aux = errno
+aux = errno rseq
elide-routines.os = libc-tls
static-only-routines = elf-init
csu-dummies = $(filter-out $(start-installed-name),crt1.o Mcrt1.o)
diff --git a/csu/Versions b/csu/Versions
index 43010c3443..0f44ebf991 100644
--- a/csu/Versions
+++ b/csu/Versions
@@ -7,6 +7,9 @@ libc {
# New special glibc functions.
gnu_get_libc_release; gnu_get_libc_version;
}
+ GLIBC_2.29 {
+ __rseq_abi;
+ }
GLIBC_PRIVATE {
errno;
}
diff --git a/csu/rseq.c b/csu/rseq.c
new file mode 100644
index 0000000000..17d553324d
--- /dev/null
+++ b/csu/rseq.c
@@ -0,0 +1,38 @@
+/* Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 2018.
+
+ 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
+ <http://www.gnu.org/licenses/>. */
+
+#include <stdint.h>
+
+enum libc_rseq_cpu_id_state {
+ LIBC_RSEQ_CPU_ID_UNINITIALIZED = -1,
+ LIBC_RSEQ_CPU_ID_REGISTRATION_FAILED = -2,
+};
+
+/* linux/rseq.h defines struct rseq as aligned on 32 bytes. The kernel ABI
+ size is 20 bytes. */
+struct libc_rseq {
+ uint32_t cpu_id_start;
+ uint32_t cpu_id;
+ uint64_t rseq_cs;
+ uint32_t flags;
+} __attribute__((aligned(4 * sizeof(uint64_t))));
+
+__attribute__((weak))
+__thread volatile struct libc_rseq __rseq_abi = {
+ .cpu_id = LIBC_RSEQ_CPU_ID_UNINITIALIZED,
+};
diff --git a/nptl/Makefile b/nptl/Makefile
index be8066524c..9def8b3f13 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -145,7 +145,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
mtx_destroy mtx_init mtx_lock mtx_timedlock \
mtx_trylock mtx_unlock call_once cnd_broadcast \
cnd_destroy cnd_init cnd_signal cnd_timedwait cnd_wait \
- tss_create tss_delete tss_get tss_set
+ tss_create tss_delete tss_get tss_set rseq
# pthread_setuid pthread_seteuid pthread_setreuid \
# pthread_setresuid \
# pthread_setgid pthread_setegid pthread_setregid \
diff --git a/nptl/Versions b/nptl/Versions
index e7f691da7a..f7890f73fc 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -277,6 +277,10 @@ libpthread {
cnd_timedwait; cnd_wait; tss_create; tss_delete; tss_get; tss_set;
}

+ GLIBC_2.29 {
+ __rseq_refcount;
+ }
+
GLIBC_PRIVATE {
__pthread_initialize_minimal;
__pthread_clock_gettime; __pthread_clock_settime;
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 907411d5bc..ab17bbb6e4 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -279,6 +279,9 @@ __pthread_initialize_minimal_internal (void)
THREAD_SETMEM (pd, cpuclock_offset, GL(dl_cpuclock_offset));
#endif

+ /* Register rseq ABI to the kernel. */
+ (void) __rseq_register_current_thread ();
+
/* Initialize the robust mutex data. */
{
#if __PTHREAD_MUTEX_HAVE_PREV
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 13bdb11133..aba641c170 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -605,6 +605,9 @@ extern void __shm_directory_freeres (void) attribute_hidden;

extern void __wait_lookup_done (void) attribute_hidden;

+extern int __rseq_register_current_thread (void) attribute_hidden;
+extern int __rseq_unregister_current_thread (void) attribute_hidden;
+
#ifdef SHARED
# define PTHREAD_STATIC_FN_REQUIRE(name)
#else
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index fe75d04113..a5233cdf2f 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -378,6 +378,7 @@ __free_tcb (struct pthread *pd)
START_THREAD_DEFN
{
struct pthread *pd = START_THREAD_SELF;
+ bool has_rseq = false;

#if HP_TIMING_AVAIL
/* Remember the time when the thread was started. */
@@ -396,6 +397,9 @@ START_THREAD_DEFN
if (__glibc_unlikely (atomic_exchange_acq (&pd->setxid_futex, 0) == -2))
futex_wake (&pd->setxid_futex, 1, FUTEX_PRIVATE);

+ /* Register rseq TLS to the kernel. */
+ has_rseq = !__rseq_register_current_thread ();
+
#ifdef __NR_set_robust_list
# ifndef __ASSUME_SET_ROBUST_LIST
if (__set_robust_list_avail >= 0)
@@ -573,6 +577,10 @@ START_THREAD_DEFN
}
#endif

+ /* Unregister rseq TLS from kernel. */
+ if (has_rseq && __rseq_unregister_current_thread ())
+ abort();
+
advise_stack_range (pd->stackblock, pd->stackblock_size, (uintptr_t) pd,
pd->guardsize);

diff --git a/nptl/rseq.c b/nptl/rseq.c
new file mode 100644
index 0000000000..415674964f
--- /dev/null
+++ b/nptl/rseq.c
@@ -0,0 +1,42 @@
+/* Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 2018.
+
+ 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
+ <http://www.gnu.org/licenses/>. */
+
+#include "pthreadP.h"
+
+__attribute__((weak))
+__thread volatile uint32_t __rseq_refcount;
+
+#ifdef __NR_rseq
+#include <sysdeps/unix/sysv/linux/rseq-internal.h>
+#else
+#include <sysdeps/nptl/rseq-internal.h>
+#endif /* __NR_rseq. */
+
+int
+attribute_hidden
+__rseq_register_current_thread (void)
+{
+ return sysdep_rseq_register_current_thread ();
+}
+
+int
+attribute_hidden
+__rseq_unregister_current_thread (void)
+{
+ return sysdep_rseq_register_current_thread ();
+}
diff --git a/sysdeps/nptl/rseq-internal.h b/sysdeps/nptl/rseq-internal.h
new file mode 100644
index 0000000000..96422ebd57
--- /dev/null
+++ b/sysdeps/nptl/rseq-internal.h
@@ -0,0 +1,34 @@
+/* Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 2018.
+
+ 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef RSEQ_INTERNAL_H
+#define RSEQ_INTERNAL_H
+
+static inline int
+sysdep_rseq_register_current_thread (void)
+{
+ return -1;
+}
+
+static inline int
+sysdep_rseq_unregister_current_thread (void)
+{
+ return -1;
+}
+
+#endif /* rseq-internal.h */
diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
new file mode 100644
index 0000000000..a7d59c8a2a
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -0,0 +1,72 @@
+/* Copyright (C) 2018 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+ Contributed by Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 2018.
+
+ 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
+ <http://www.gnu.org/licenses/>. */
+
+#ifndef RSEQ_INTERNAL_H
+#define RSEQ_INTERNAL_H
+
+#include <stdint.h>
+#include <linux/rseq.h>
+
+#define RSEQ_SIG 0x53053053
+
+extern __thread volatile struct rseq __rseq_abi
+__attribute__ ((tls_model ("initial-exec")));
+
+extern __thread volatile uint32_t __rseq_refcount
+__attribute__ ((tls_model ("initial-exec")));
+
+static inline int
+sysdep_rseq_register_current_thread (void)
+{
+ int rc, ret = 0;
+ INTERNAL_SYSCALL_DECL (err);
+
+ if (__rseq_abi.cpu_id == RSEQ_CPU_ID_REGISTRATION_FAILED)
+ return -1;
+ if (atomic_increment_val (&__rseq_refcount) - 1)
+ goto end;
+ rc = INTERNAL_SYSCALL_CALL (rseq, err, &__rseq_abi, sizeof (struct rseq),
+ 0, RSEQ_SIG);
+ if (!rc)
+ goto end;
+ if (INTERNAL_SYSCALL_ERRNO (rc, err) != EBUSY)
+ __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+ ret = -1;
+ atomic_decrement (&__rseq_refcount);
+end:
+ return ret;
+}
+
+static inline int
+sysdep_rseq_unregister_current_thread (void)
+{
+ int rc, ret = 0;
+ INTERNAL_SYSCALL_DECL (err);
+
+ if (atomic_decrement_val (&__rseq_refcount))
+ goto end;
+ rc = INTERNAL_SYSCALL_CALL (rseq, err, &__rseq_abi, sizeof (struct rseq),
+ RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+ if (!rc)
+ goto end;
+ ret = -1;
+end:
+ return ret;
+}
+
+#endif /* rseq-internal.h */
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
index 816e4a7426..6ef92778fc 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
@@ -1895,6 +1895,7 @@ GLIBC_2.28 thrd_current F
GLIBC_2.28 thrd_equal F
GLIBC_2.28 thrd_sleep F
GLIBC_2.28 thrd_yield F
+GLIBC_2.29 __rseq_abi D
GLIBC_2.3 __ctype_b_loc F
GLIBC_2.3 __ctype_tolower_loc F
GLIBC_2.3 __ctype_toupper_loc F
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
index 931c8277a8..2cbb8882eb 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
+++ b/sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
@@ -219,6 +219,7 @@ GLIBC_2.28 tss_create F
GLIBC_2.28 tss_delete F
GLIBC_2.28 tss_get F
GLIBC_2.28 tss_set F
+GLIBC_2.29 __rseq_refcount D
GLIBC_2.3.2 pthread_cond_broadcast F
GLIBC_2.3.2 pthread_cond_destroy F
GLIBC_2.3.2 pthread_cond_init F
--
2.17.1