1/*
2 * Copyright (c) 2006 Apple Computer, Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28
29
30/*
31 * [SPN] Support for _POSIX_SPAWN
32 *
33 * This file contains internal data structures which are externally represented
34 * as opaque void pointers to prevent introspection. This permits us to
35 * change the underlying implementation of the code to maintain it or to
36 * support new features, as needed, without the consumer needing to recompile
37 * their code because of structure size changes or data reorganization.
38 */
39
40#ifndef _SYS_SPAWN_INTERNAL_H_
41#define _SYS_SPAWN_INTERNAL_H_
42
43#include <sys/_types.h> /* __offsetof(), __darwin_size_t */
44#include <sys/param.h>
45#include <sys/syslimits.h> /* PATH_MAX */
46#include <sys/spawn.h>
47#include <mach/machine.h>
48#include <mach/port.h>
49#include <mach/exception_types.h>
50#include <mach/coalition.h> /* COALITION_NUM_TYPES */
51#include <mach/task_policy.h>
52#include <os/overflow.h>
53#include <mach/mach_param.h>
54
55/*
56 * Safely compute the size in bytes of a structure, '_type', whose last
57 * element, '_member', is a zero-sized array meant to hold 'x' bytes.
58 *
59 * If the size calculation overflows a size_t value, this macro returns 0.
60 */
61#define PS_ACTION_SIZE(x, _type, _member_type) ({\
62 size_t _ps_count = (size_t)x; \
63 size_t _ps_size = 0; \
64 /* (count * sizeof(_member_type)) + sizeof(_type) */ \
65 if (os_mul_and_add_overflow(_ps_count, \
66 sizeof(_member_type), \
67 sizeof(_type), \
68 &_ps_size)) { \
69 _ps_size = 0; \
70 } \
71 _ps_size; })
72
73/*
74 * Allowable posix_spawn() port action types
75 */
76typedef enum {
77 PSPA_SPECIAL = 0,
78 PSPA_EXCEPTION = 1,
79 PSPA_AU_SESSION = 2,
80 PSPA_IMP_WATCHPORTS = 3,
81 PSPA_REGISTERED_PORTS = 4,
82 PSPA_PTRAUTH_TASK_PORT = 5,
83} pspa_t;
84
85/*
86 * Internal representation of one port to be set on posix_spawn().
87 * Currently this is limited to setting special and exception ports,
88 * but could be extended to other inheritable port types.
89 */
90typedef struct _ps_port_action {
91 pspa_t port_type;
92 exception_mask_t mask;
93 mach_port_name_t new_port;
94 exception_behavior_t behavior;
95 thread_state_flavor_t flavor;
96 int which;
97} _ps_port_action_t;
98
99/*
100 * A collection of port actions to take on the newly spawned process.
101 */
102typedef struct _posix_spawn_port_actions {
103 int pspa_alloc;
104 int pspa_count;
105 _ps_port_action_t pspa_actions[];
106} *_posix_spawn_port_actions_t;
107
108/*
109 * Returns size in bytes of a _posix_spawn_port_actions holding x elements.
110 */
111#define PS_PORT_ACTIONS_SIZE(x) \
112 PS_ACTION_SIZE(x, struct _posix_spawn_port_actions, _ps_port_action_t)
113
114#define NBINPREFS 4
115
116/*
117 * Mapping of opaque data pointer to a MAC policy (specified by name).
118 */
119typedef struct _ps_mac_policy_extension {
120 char policyname[128];
121 union {
122 /* Address of the user space data passed into kernel space */
123 uint64_t data;
124 /* In kernel space, offset into the pool of all extensions' data */
125 uint64_t dataoff;
126 };
127 uint64_t datalen;
128} _ps_mac_policy_extension_t;
129
130/*
131 * A collection of extra data passed to MAC policies for the newly spawned process.
132 */
133typedef struct _posix_spawn_mac_policy_extensions {
134 int psmx_alloc;
135 int psmx_count;
136 _ps_mac_policy_extension_t psmx_extensions[];
137} *_posix_spawn_mac_policy_extensions_t;
138
139/*
140 * Returns size in bytes of a _posix_spawn_mac_policy_extensions holding x elements.
141 */
142#define PS_MAC_EXTENSIONS_SIZE(x) \
143 PS_ACTION_SIZE(x, struct _posix_spawn_mac_policy_extensions, _ps_mac_policy_extension_t)
144
145#define PS_MAC_EXTENSIONS_INIT_COUNT 2
146
147/*
148 * Coalition posix spawn attributes
149 */
150struct _posix_spawn_coalition_info {
151 struct {
152 uint64_t psci_id;
153 uint32_t psci_role;
154 uint32_t psci_reserved1;
155 uint64_t psci_reserved2;
156 } psci_info[COALITION_NUM_TYPES];
157};
158
159/*
160 * UID/GID attributes
161 */
162struct _posix_spawn_posix_cred_info {
163 uint32_t pspci_flags; /* spawn persona flags */
164 uid_t pspci_uid; /* alternate posix/unix UID */
165 gid_t pspci_gid; /* alternate posix/unix GID */
166 uint32_t pspci_ngroups; /* alternate advisory groups */
167 gid_t pspci_groups[NGROUPS];
168 uid_t pspci_gmuid; /* group membership UID */
169 char pspci_login[MAXLOGNAME + 1];
170};
171
172#define POSIX_SPAWN_POSIX_CRED_UID 0x00010000
173#define POSIX_SPAWN_POSIX_CRED_GID 0x00020000
174#define POSIX_SPAWN_POSIX_CRED_GROUPS 0x00040000
175#define POSIX_SPAWN_POSIX_CRED_LOGIN 0x00080000
176
177/*
178 * Persona attributes
179 */
180struct _posix_spawn_persona_info {
181 uid_t pspi_id; /* persona ID (unix UID) */
182 uint32_t pspi_flags; /* spawn persona flags */
183 uid_t pspi_uid; /* alternate posix/unix UID */
184 gid_t pspi_gid; /* alternate posix/unix GID */
185 uint32_t pspi_ngroups; /* alternate advisory groups */
186 gid_t pspi_groups[NGROUPS];
187 uid_t pspi_gmuid; /* group membership UID */
188};
189
190#define POSIX_SPAWN_PERSONA_FLAGS_NONE 0x0
191#define POSIX_SPAWN_PERSONA_FLAGS_OVERRIDE 0x1 /* noop, the only option */
192#define POSIX_SPAWN_PERSONA_FLAGS_VERIFY 0x2 /* noop, unimplemented */
193
194#define POSIX_SPAWN_PERSONA_ALL_FLAGS \
195 (POSIX_SPAWN_PERSONA_FLAGS_OVERRIDE \
196 | POSIX_SPAWN_PERSONA_FLAGS_VERIFY \
197 )
198
199#define POSIX_SPAWN_PERSONA_UID POSIX_SPAWN_POSIX_CRED_UID
200#define POSIX_SPAWN_PERSONA_GID POSIX_SPAWN_POSIX_CRED_GID
201#define POSIX_SPAWN_PERSONA_GROUPS POSIX_SPAWN_POSIX_CRED_GROUPS
202
203
204/*
205 * A posix_spawnattr structure contains all of the attribute elements that
206 * can be set, as well as any metadata whose validity is signalled by the
207 * presence of a bit in the flags field. All fields are initialized to the
208 * appropriate default values by posix_spawnattr_init().
209 *
210 * Fields must be added at the end of this, but before extensions array
211 * pointers.
212 */
213
214typedef struct _posix_spawnattr {
215 short psa_flags; /* spawn attribute flags */
216 short flags_padding; /* get the flags to be int aligned */
217 sigset_t psa_sigdefault; /* signal set to default */
218 sigset_t psa_sigmask; /* signal set to mask */
219 pid_t psa_pgroup; /* pgroup to spawn into */
220 cpu_type_t psa_binprefs[NBINPREFS]; /* cpu affinity prefs*/
221 int psa_pcontrol; /* process control bits on resource starvation */
222 int psa_apptype; /* app type and process spec behav */
223 uint64_t psa_cpumonitor_percent; /* CPU usage monitor percentage */
224 uint64_t psa_cpumonitor_interval; /* CPU usage monitor interval, in seconds */
225 uint64_t psa_reserved;
226
227 short psa_jetsam_flags; /* jetsam flags */
228 short short_padding; /* Padding for alignment issues */
229 int psa_priority; /* jetsam relative importance */
230 int psa_memlimit_active; /* jetsam memory limit (in MB) when process is active */
231 int psa_memlimit_inactive; /* jetsam memory limit (in MB) when process is inactive */
232
233 uint64_t psa_qos_clamp; /* QoS Clamp to set on the new process */
234 task_role_t psa_darwin_role; /* PRIO_DARWIN_ROLE to set on the new process */
235 int psa_thread_limit; /* thread limit */
236
237 uint64_t psa_max_addr; /* Max valid VM address */
238 bool psa_no_smt;
239 bool psa_tecs;
240 int psa_platform; /* Plaform for the binary */
241
242 cpu_subtype_t psa_subcpuprefs[NBINPREFS]; /* subcpu affinity prefs*/
243 uint32_t psa_options; /* More options to be passed to posix_spawn */
244 uint32_t psa_port_soft_limit; /* port space soft limit */
245 uint32_t psa_port_hard_limit; /* port space hard limit */
246 uint32_t psa_filedesc_soft_limit; /* file descriptor soft limit */
247 uint32_t psa_filedesc_hard_limit; /* file descriptor hard limit */
248 uint32_t psa_crash_behavior; /* crash behavior flags */
249 int psa_dataless_iopolicy; /* materialize dataless iopolicy parameter */
250 uint64_t psa_crash_behavior_deadline; /* crash behavior deadline */
251 uint8_t psa_launch_type; /* type of launch for launch constraint enforcement */
252
253 /* For exponential backoff */
254 uint32_t psa_crash_count;
255 uint32_t psa_throttle_timeout;
256
257 uint32_t psa_kqworkloop_soft_limit; /* kqworkloop soft limit */
258 uint32_t psa_kqworkloop_hard_limit; /* kqworkloop hard limit */
259
260 /*
261 * NOTE: Extensions array pointers must stay at the end so that
262 * everything above this point stays the same size on different bitnesses
263 * see <rdar://problem/12858307>
264 */
265 _posix_spawn_port_actions_t psa_ports; /* special/exception ports */
266 _posix_spawn_mac_policy_extensions_t psa_mac_extensions; /* MAC policy-specific extensions. */
267 struct _posix_spawn_coalition_info *psa_coalition_info; /* coalition info */
268 struct _posix_spawn_persona_info *psa_persona_info; /* spawn new process into given persona */
269 struct _posix_spawn_posix_cred_info *psa_posix_cred_info; /* posix creds: uid/gid/groups */
270 char *psa_subsystem_root_path; /* pass given path in apple strings */
271 char *psa_conclave_id; /* conclave string */
272} *_posix_spawnattr_t;
273
274/*
275 * Jetsam flags eg: psa_jetsam_flags
276 */
277#define POSIX_SPAWN_JETSAM_SET 0x8000
278
279#define POSIX_SPAWN_JETSAM_USE_EFFECTIVE_PRIORITY 0x01
280#define POSIX_SPAWN_JETSAM_HIWATER_BACKGROUND 0x02 /* to be deprecated */
281#define POSIX_SPAWN_JETSAM_MEMLIMIT_FATAL 0x04 /* to be deprecated */
282
283/*
284 * Additional flags available for use with
285 * the posix_spawnattr_setjetsam_ext() call
286 */
287#define POSIX_SPAWN_JETSAM_MEMLIMIT_ACTIVE_FATAL 0x04 /* if set, limit is fatal when the process is active */
288#define POSIX_SPAWN_JETSAM_MEMLIMIT_INACTIVE_FATAL 0x08 /* if set, limit is fatal when the process is inactive */
289
290
291/*
292 * Flags set based on posix_spawnattr_set_jetsam_ttr_np().
293 * Indicate relaunch behavior of process when jetsammed
294 */
295/* Mask and bucket counts for relaunch behavior */
296#define POSIX_SPAWN_JETSAM_RELAUNCH_BEHAVIOR_BUCKETS (0x3)
297#define POSIX_SPAWN_JETSAM_RELAUNCH_BEHAVIOR_MASK (0x30)
298
299/* Actual buckets based on behavior data */
300#define POSIX_SPAWN_JETSAM_RELAUNCH_BEHAVIOR_HIGH (0x30)
301#define POSIX_SPAWN_JETSAM_RELAUNCH_BEHAVIOR_MED (0x20)
302#define POSIX_SPAWN_JETSAM_RELAUNCH_BEHAVIOR_LOW (0x10)
303
304/*
305 * Deprecated posix_spawn psa_flags values
306 *
307 * POSIX_SPAWN_OSX_TALAPP_START 0x0400
308 * POSIX_SPAWN_IOS_RESV1_APP_START 0x0400
309 * POSIX_SPAWN_IOS_APPLE_DAEMON_START 0x0800
310 * POSIX_SPAWN_IOS_APP_START 0x1000
311 * POSIX_SPAWN_OSX_WIDGET_START 0x0800
312 * POSIX_SPAWN_OSX_DBCLIENT_START 0x0800
313 * POSIX_SPAWN_OSX_RESVAPP_START 0x1000
314 */
315
316/*
317 * Deprecated posix_spawn psa_apptype values
318 *
319 * POSIX_SPAWN_PROCESS_TYPE_APPLEDAEMON 0x00000001
320 * POSIX_SPAWN_PROCESS_TYPE_UIAPP 0x00000002
321 * POSIX_SPAWN_PROCESS_TYPE_ADAPTIVE 0x00000004
322 * POSIX_SPAWN_PROCESS_TYPE_TAL 0x00000001
323 * POSIX_SPAWN_PROCESS_TYPE_WIDGET 0x00000002
324 * POSIX_SPAWN_PROCESS_TYPE_DELAYIDLESLEEP 0x10000000
325 *
326 * POSIX_SPAWN_PROCESS_FLAG_IMPORTANCE_DONOR 0x00000010
327 * POSIX_SPAWN_PROCESS_FLAG_ADAPTIVE 0x00000020
328 * POSIX_SPAWN_PROCESS_FLAG_START_BACKGROUND 0x00000040
329 * POSIX_SPAWN_PROCESS_FLAG_START_LIGHT_THROTTLE 0x00000080
330 */
331
332/*
333 * posix_spawn psa_apptype process type settings.
334 * when POSIX_SPAWN_PROC_TYPE is set, old psa_apptype bits are ignored
335 */
336#define POSIX_SPAWN_PROCESS_TYPE_NORMAL 0x00000000
337#define POSIX_SPAWN_PROCESS_TYPE_DEFAULT POSIX_SPAWN_PROCESS_TYPE_NORMAL
338
339#define POSIX_SPAWN_PROC_TYPE_MASK 0x00000F00
340
341#define POSIX_SPAWN_PROC_TYPE_APP_DEFAULT 0x00000100
342#define POSIX_SPAWN_PROC_TYPE_APP_TAL 0x00000200 /* unused */
343
344#define POSIX_SPAWN_PROC_TYPE_DAEMON_STANDARD 0x00000300
345#define POSIX_SPAWN_PROC_TYPE_DAEMON_INTERACTIVE 0x00000400
346#define POSIX_SPAWN_PROC_TYPE_DAEMON_BACKGROUND 0x00000500
347#define POSIX_SPAWN_PROC_TYPE_DAEMON_ADAPTIVE 0x00000600
348
349#define POSIX_SPAWN_PROC_TYPE_DRIVER 0x00000700
350
351#define POSIX_SPAWN_PROC_CLAMP_NONE 0x00000000
352#define POSIX_SPAWN_PROC_CLAMP_UTILITY 0x00000001
353#define POSIX_SPAWN_PROC_CLAMP_BACKGROUND 0x00000002
354#define POSIX_SPAWN_PROC_CLAMP_MAINTENANCE 0x00000003
355#define POSIX_SPAWN_PROC_CLAMP_LAST 0x00000004
356
357#define POSIX_SPAWN_ENTITLEMENT_DRIVER "com.apple.private.spawn-driver"
358/* Setting to indicate no change to darwin role */
359#define POSIX_SPAWN_DARWIN_ROLE_NONE 0x00000000
360/* Other possible values are specified by PRIO_DARWIN_ROLE in sys/resource.h */
361
362/* Other posix spawn options passed through psa_options */
363__options_decl(posix_spawn_options, uint32_t, {
364 PSA_OPTION_NONE = 0,
365 PSA_OPTION_PLUGIN_HOST_DISABLE_A_KEYS = 0x1,
366 PSA_OPTION_ALT_ROSETTA = 0x2,
367 PSA_OPTION_DATALESS_IOPOLICY = 0x4,
368 PSA_OPTION_USE_SEC_TRANSITION_SHIMS = 0x8,
369});
370
371/*
372 * Allowable posix_spawn() file actions
373 */
374typedef enum {
375 PSFA_OPEN = 0,
376 PSFA_CLOSE = 1,
377 PSFA_DUP2 = 2,
378 PSFA_INHERIT = 3,
379 PSFA_FILEPORT_DUP2 = 4,
380 PSFA_CHDIR = 5,
381 PSFA_FCHDIR = 6
382} psfa_t;
383
384
385/*
386 * A posix_spawn() file action record for a single action
387 *
388 * Notes: We carry around the full open arguments for both the open
389 * and the close to permit the use of a single array of action
390 * elements to be associated with a file actions object.
391 *
392 * A possible future optimization would be to break this into
393 * a variable sized vector list to save space (i.e. a separate
394 * string area, allocation of least amount of path buffer per
395 * open action, etc.).
396 */
397typedef struct _psfa_action {
398 psfa_t psfaa_type; /* file action type */
399 union {
400 int psfaa_filedes; /* fd to operate on */
401 mach_port_name_t psfaa_fileport; /* fileport to operate on */
402 };
403 union {
404 struct {
405 int psfao_oflag; /* open flags to use */
406 mode_t psfao_mode; /* mode for open */
407 char psfao_path[PATH_MAX]; /* path to open */
408 } psfaa_openargs;
409 struct {
410 int psfad_newfiledes; /* new file descriptor to use */
411 } psfaa_dup2args;
412 struct {
413 char psfac_path[PATH_MAX]; /* path to chdir */
414 } psfaa_chdirargs;
415 };
416} _psfa_action_t;
417
418
419/*
420 * Internal representation of posix_spawn() file actions structure
421 *
422 * Notes: This is implemented as a structure followed by an array of
423 * file action records. The psfa_act_alloc value is the number
424 * of elements allocated in this array, and the psfa_act_count is
425 * the number of elements currently in use (to permit some form
426 * of preallocation, e.g. a power of 2 growth for reallocation,
427 * etc.).
428 *
429 * A possible future optimization would keep a size value and
430 * a structure base reference pointer to permit copyin to the
431 * kernel directly as a single blob, without damaging relative
432 * internal pointer math. It's probably better that this be a
433 * long long rather than a true pointer, to make it invariant
434 * for 32 vs. 64 bt programming SPIs.
435 */
436typedef struct _posix_spawn_file_actions {
437 int psfa_act_alloc; /* available actions space */
438 int psfa_act_count; /* count of defined actions */
439 _psfa_action_t psfa_act_acts[]; /* actions array (uses c99) */
440} *_posix_spawn_file_actions_t;
441
442/*
443 * Calculate the size of a structure, given the number of elements that it is
444 * capable of containing.
445 */
446#define PSF_ACTIONS_SIZE(x) \
447 PS_ACTION_SIZE(x, struct _posix_spawn_file_actions, _psfa_action_t)
448
449/*
450 * Initial count of actions in a struct _posix_spawn_file_actions after it is
451 * first allocated; this should be non-zero, since we expect that one would not
452 * have been allocated unless there was an intent to use it.
453 */
454#define PSF_ACTIONS_INIT_COUNT 2
455
456/*
457 * Structure defining the true third argument to the posix_spawn() system call
458 * entry point; we wrap it and pass a descriptor so that we can know the
459 * copyin size ahead of time, and deal with copying in variant lists of things
460 * as single monolithic units, instead of many individual elements. This is a
461 * performance optimization.
462 */
463struct _posix_spawn_args_desc {
464 __darwin_size_t attr_size; /* size of attributes block */
465 _posix_spawnattr_t attrp; /* pointer to block */
466 __darwin_size_t file_actions_size; /* size of file actions block */
467 _posix_spawn_file_actions_t
468 file_actions; /* pointer to block */
469 __darwin_size_t port_actions_size; /* size of port actions block */
470 _posix_spawn_port_actions_t
471 port_actions; /* pointer to port block */
472 __darwin_size_t mac_extensions_size;
473 _posix_spawn_mac_policy_extensions_t
474 mac_extensions; /* pointer to policy-specific
475 * attributes */
476 __darwin_size_t coal_info_size;
477 struct _posix_spawn_coalition_info *coal_info; /* pointer to coalition info */
478
479 __darwin_size_t persona_info_size;
480 struct _posix_spawn_persona_info *persona_info;
481
482 __darwin_size_t posix_cred_info_size;
483 struct _posix_spawn_posix_cred_info *posix_cred_info;
484
485 __darwin_size_t subsystem_root_path_size;
486 char *subsystem_root_path;
487
488 __darwin_size_t conclave_id_size;
489 char *conclave_id;
490};
491
492#ifdef KERNEL
493#include <sys/appleapiopts.h>
494#ifdef __APPLE_API_PRIVATE
495
496#if __DARWIN_ALIGN_NATURAL
497#pragma options align=natural
498#endif
499
500struct user32__posix_spawn_args_desc {
501 uint32_t attr_size; /* size of attributes block */
502 uint32_t attrp; /* pointer to block */
503 uint32_t file_actions_size; /* size of file actions block */
504 uint32_t file_actions; /* pointer to block */
505 uint32_t port_actions_size; /* size of port actions block */
506 uint32_t port_actions; /* pointer to block */
507 uint32_t mac_extensions_size;
508 uint32_t mac_extensions;
509 uint32_t coal_info_size;
510 uint32_t coal_info;
511 uint32_t persona_info_size;
512 uint32_t persona_info;
513 uint32_t posix_cred_info_size;
514 uint32_t posix_cred_info;
515 uint32_t subsystem_root_path_size;
516 uint32_t subsystem_root_path;
517 uint32_t conclave_id_size;
518 uint32_t conclave_id;
519};
520
521struct user__posix_spawn_args_desc {
522 user_size_t attr_size; /* size of attributes block */
523 user_addr_t attrp; /* pointer to block */
524 user_size_t file_actions_size; /* size of file actions block */
525 user_addr_t file_actions; /* pointer to block */
526 user_size_t port_actions_size; /* size of port actions block */
527 user_addr_t port_actions; /* pointer to block */
528 user_size_t mac_extensions_size; /* size of MAC-specific attrs. */
529 user_addr_t mac_extensions; /* pointer to block */
530 user_size_t coal_info_size;
531 user_addr_t coal_info;
532 user_size_t persona_info_size;
533 user_addr_t persona_info;
534 user_size_t posix_cred_info_size;
535 user_addr_t posix_cred_info;
536 user_size_t subsystem_root_path_size;
537 user_addr_t subsystem_root_path;
538 user_size_t conclave_id_size;
539 user_addr_t conclave_id;
540};
541
542
543#if __DARWIN_ALIGN_NATURAL
544#pragma options align=reset
545#endif
546
547#endif /* __APPLE_API_PRIVATE */
548#endif /* KERNEL */
549
550#endif /* _SYS_SPAWN_INTERNAL_H_ */
551