san/ubsan_log.c

   1 /*
   2  * Copyright (c) 2018 Apple 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 #include <os/atomic_private.h>
  30 #include <kern/cpu_data.h>
  31 #include <kern/kalloc.h>
  32 #include <kern/simple_lock.h> // hw_wait_while_equals
  33 #include <libkern/libkern.h>
  34 #include <sys/sysctl.h>
  35 #include "ubsan.h"
  36
  37 /*
  38  * To dump the violation log:
  39  *   $ sysctl kern.ubsan.log
  40  *
  41  * To reset:
  42  *   $ sysctl kern.ubsan.logentries=0
  43  */
  44
  45 static const size_t ubsan_log_size = 2048;
  46 struct ubsan_violation ubsan_log[ubsan_log_size];
  47
  48 /*
  49  * Implement a fixed-size buffer FIFO, similar to the Chase-Lev DeQueue.
  50  *
  51  * See https://fzn.fr/readings/ppopp13.pdf for explanations on barriers.
  52  */
  53 _Atomic size_t ubsan_log_head = 0; /* first valid entry */
  54 _Atomic size_t ubsan_log_tail = 0; /* next free slot (reader) */
  55 _Atomic size_t ubsan_log_next = 0; /* next free slot (writer) */
  56
  57 static const bool ubsan_logging = true;
  58
  59 static inline size_t
  60 next_entry(size_t x)
  61 {
  62         return (x + 1) % ubsan_log_size;
  63 }
  64
  65 void
  66 ubsan_log_append(struct ubsan_violation *violation)
  67 {
  68         if (!ubsan_logging) {
  69                 return;
  70         }
  71
  72         /* reserve a slot */
  73         size_t i, e, n;
  74
  75         disable_preemption();
  76
  77         os_atomic_rmw_loop(&ubsan_log_next, i, n, relaxed, {
  78                 n = next_entry(i);
  79                 if (n == os_atomic_load(&ubsan_log_tail, acquire)) {
  80                         enable_preemption();
  81                         return; /* full */
  82                 }
  83         });
  84
  85         ubsan_log[i] = *violation;
  86         os_atomic_thread_fence(release);
  87
  88         /* make the entry available */
  89 again:
  90         os_atomic_rmw_loop(&ubsan_log_head, e, n, relaxed, {
  91                 if (e != i) {
  92                         // we need to wait for another enqueuer
  93                         os_atomic_rmw_loop_give_up({
  94                                 hw_wait_while_equals((void **)&ubsan_log_head, (void *)e);
  95                                 goto again;
  96                         });
  97                 }
  98         });
  99
 100         enable_preemption();
 101 }
 102
 103 static int
 104 sysctl_ubsan_log_dump SYSCTL_HANDLER_ARGS
 105 {
 106 #pragma unused(oidp, arg1, arg2)
 107         const size_t sz = ubsan_log_size * 256;
 108         size_t head, tail;
 109
 110         head = os_atomic_load(&ubsan_log_head, relaxed);
 111         os_atomic_thread_fence(seq_cst);
 112         tail = os_atomic_load(&ubsan_log_tail, relaxed);
 113
 114         char *buf;
 115         size_t n = 0;
 116         int err;
 117
 118         if (tail == head) {
 119                 return 0; /* log is empty */
 120         }
 121
 122         buf = kheap_alloc(KHEAP_TEMP, sz, Z_WAITOK | Z_ZERO);
 123         if (!buf) {
 124                 return 0;
 125         }
 126
 127         for (size_t i = tail; i != head; i = next_entry(i)) {
 128                 n += ubsan_format(&ubsan_log[i], buf + n, sz - n);
 129         }
 130
 131         err = SYSCTL_OUT(req, buf, n);
 132
 133         kheap_free(KHEAP_TEMP, buf, sz);
 134         return err;
 135 }
 136
 137 static int
 138 sysctl_ubsan_log_entries SYSCTL_HANDLER_ARGS
 139 {
 140 #pragma unused(oidp, arg1, arg2)
 141         int ch, err, val;
 142         size_t head, tail;
 143
 144         size_t nentries;
 145
 146         head = os_atomic_load(&ubsan_log_head, relaxed);
 147         os_atomic_thread_fence(seq_cst);
 148         tail = os_atomic_load(&ubsan_log_tail, relaxed);
 149
 150         if (head >= tail) {
 151                 nentries = head - tail;
 152         } else {
 153                 nentries = ubsan_log_size - (tail - head + 1);
 154         }
 155
 156         err = sysctl_io_number(req, nentries, sizeof(nentries), &val, &ch);
 157         if (err == 0 && ch) {
 158                 if (val != 0) {
 159                         err = EINVAL;
 160                 } else {
 161                         os_atomic_store(&ubsan_log_tail, head, relaxed);
 162                 }
 163         }
 164
 165         return err;
 166 }
 167
 168 SYSCTL_DECL(ubsan);
 169 SYSCTL_NODE(_kern, OID_AUTO, ubsan, CTLFLAG_RW | CTLFLAG_LOCKED, 0, "");
 170
 171 SYSCTL_COMPAT_UINT(_kern_ubsan, OID_AUTO, logsize, CTLFLAG_RD, NULL, (unsigned)ubsan_log_size, "");
 172
 173 SYSCTL_PROC(_kern_ubsan, OID_AUTO, logentries,
 174     CTLTYPE_INT | CTLFLAG_RW,
 175     0, 0, sysctl_ubsan_log_entries, "I", "");
 176
 177 SYSCTL_PROC(_kern_ubsan, OID_AUTO, log,
 178     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MASKED,
 179     0, 0, sysctl_ubsan_log_dump, "A", "");