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 <stdatomic.h>
  30 #include <kern/kalloc.h>
  31 #include <libkern/libkern.h>
  32 #include <sys/sysctl.h>
  33 #include "ubsan.h"
  34
  35 /*
  36  * To dump the violation log:
  37  *   $ sysctl kern.ubsan.log
  38  *
  39  * To reset:
  40  *   $ sysctl kern.ubsan.logentries=0
  41  */
  42
  43 static const size_t ubsan_log_size = 2048;
  44 struct ubsan_violation ubsan_log[ubsan_log_size];
  45
  46 _Atomic size_t ubsan_log_head = 0; /* first valid entry */
  47 _Atomic size_t ubsan_log_tail = 0; /* next free slot (reader) */
  48 _Atomic size_t ubsan_log_next = 0; /* next free slot (writer) */
  49
  50 static const bool ubsan_logging = true;
  51
  52 static inline size_t
  53 next_entry(size_t x)
  54 {
  55         return (x + 1) % ubsan_log_size;
  56 }
  57
  58 void
  59 ubsan_log_append(struct ubsan_violation *e)
  60 {
  61         if (!ubsan_logging) {
  62                 return;
  63         }
  64
  65         /* reserve a slot */
  66         size_t i = atomic_load(&ubsan_log_next);
  67         size_t n;
  68         do {
  69                 n = next_entry(i);
  70                 if (n == ubsan_log_tail) {
  71                         return; /* full */
  72                 }
  73         } while (!atomic_compare_exchange_weak(&ubsan_log_next, &i, n));
  74
  75         ubsan_log[i] = *e;
  76
  77         /* make the entry available */
  78         size_t prev;
  79         do {
  80                 prev = i;
  81         } while (!atomic_compare_exchange_weak(&ubsan_log_head, &prev, n));
  82 }
  83
  84 static int
  85 sysctl_ubsan_log_dump SYSCTL_HANDLER_ARGS
  86 {
  87 #pragma unused(oidp, arg1, arg2)
  88         const size_t sz = ubsan_log_size * 256;
  89         size_t start = atomic_load(&ubsan_log_tail);
  90         size_t end = atomic_load(&ubsan_log_head);
  91
  92         char *buf;
  93         size_t n = 0;
  94         int err;
  95
  96         if (start == end) {
  97                 return 0; /* log is empty */
  98         }
  99
 100         buf = kalloc(sz);
 101         if (!buf) {
 102                 return 0;
 103         }
 104         buf[0] = '\0';
 105
 106         for (size_t i = start; i != end; i = next_entry(i)) {
 107                 n += ubsan_format(&ubsan_log[i], buf+n, sz-n);
 108         }
 109
 110         err = SYSCTL_OUT(req, buf, n);
 111
 112         kfree(buf, sz);
 113         return err;
 114 }
 115
 116 static int
 117 sysctl_ubsan_log_entries SYSCTL_HANDLER_ARGS
 118 {
 119 #pragma unused(oidp, arg1, arg2)
 120         int ch, err, val;
 121
 122         int nentries;
 123         if (ubsan_log_head >= ubsan_log_tail) {
 124                 nentries = ubsan_log_head - ubsan_log_tail;
 125         } else {
 126                 nentries = ubsan_log_size - (ubsan_log_tail - ubsan_log_head + 1);
 127         }
 128
 129         err = sysctl_io_number(req, nentries, sizeof(nentries), &val, &ch);
 130         if (err == 0 && ch) {
 131                 if (val != 0) {
 132                         err = EINVAL;
 133                 } else {
 134                         ubsan_log_tail = ubsan_log_head;
 135                 }
 136         }
 137
 138         return err;
 139 }
 140
 141 SYSCTL_DECL(ubsan);
 142 SYSCTL_NODE(_kern, OID_AUTO, ubsan, CTLFLAG_RW | CTLFLAG_LOCKED, 0, "");
 143
 144 SYSCTL_COMPAT_UINT(_kern_ubsan, OID_AUTO, logsize, CTLFLAG_RD, NULL, (unsigned)ubsan_log_size, "");
 145
 146 SYSCTL_PROC(_kern_ubsan, OID_AUTO, logentries,
 147                 CTLTYPE_INT | CTLFLAG_RW,
 148                 0, 0, sysctl_ubsan_log_entries, "I", "");
 149
 150 SYSCTL_PROC(_kern_ubsan, OID_AUTO, log,
 151                 CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MASKED,
 152                 0, 0, sysctl_ubsan_log_dump, "A", "");