libkern/ptrauth_utils.c

   1 /*
   2  * Copyright (c) 2020 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 <IOKit/IOLib.h>
  30 #include <kern/debug.h> // for panic()
  31
  32 #include <libkern/ptrauth_utils.h>
  33
  34
  35 #if __has_feature(ptrauth_calls)
  36
  37 /*
  38  * ptrauth_utils_sign_blob_generic
  39  *
  40  * Sign a blob of data with the GA key
  41  *
  42  */
  43 __attribute__((noinline))
  44 ptrauth_generic_signature_t
  45 ptrauth_utils_sign_blob_generic(const void * ptr, size_t len_bytes, uint64_t data, int flags)
  46 {
  47         ptrauth_generic_signature_t sig = 0;
  48
  49         uint64_t rounds = len_bytes / sizeof(uintptr_t);
  50         size_t ntrailing = len_bytes % sizeof(uintptr_t);
  51         uintptr_t trailing = 0;
  52
  53         if (ptr == NULL) {
  54                 return 0;
  55         }
  56
  57         /* If address diversification is requested, mix the blob address with the salt */
  58         if (flags & PTRAUTH_ADDR_DIVERSIFY) {
  59                 data ^= (uint64_t)ptr;
  60         }
  61
  62         /* First round adds ptrauth_utils_sign_blob_generic discrimination. */
  63         sig = ptrauth_sign_generic_data(sig, ptrauth_string_discriminator("ptrauth_utils_sign_blob_generic-prologue") | 0x01);
  64
  65         /* Second round adds salt */
  66         sig = ptrauth_sign_generic_data(sig, data);
  67
  68         /* Calculate an additive signature of the buffer */
  69         for (uint64_t i = 0; i < rounds; i++) {
  70                 sig = ptrauth_sign_generic_data(*(const uintptr_t *)ptr, sig);
  71                 ptr += sizeof(uintptr_t);
  72         }
  73
  74         /* ptrauth_sign_generic_data operates on pointer-sized values only,
  75          * so we need to handle trailing bytes for the non-pointer-aligned case */
  76         if (ntrailing) {
  77                 for (int i = 0; i < ntrailing; i++) {
  78                         ((uint8_t *)&trailing)[i] = ((const uint8_t *)ptr)[i];
  79                 }
  80                 sig = ptrauth_sign_generic_data(trailing, sig);
  81         }
  82
  83
  84         /* Final round to add an additional cookie */
  85         sig = ptrauth_sign_generic_data(sig, ptrauth_string_discriminator("ptrauth_utils_sign_blob_generic-epilogue") | 0x01);
  86
  87         return sig;
  88 }
  89
  90 /*
  91  * ptrauth_utils_auth_blob_generic
  92  *
  93  * Authenticate signature produced by ptrauth_utils_sign_blob_generic
  94  */
  95 __attribute__((noinline))
  96 void
  97 ptrauth_utils_auth_blob_generic(const void * ptr, size_t len_bytes, uint64_t data, int flags, ptrauth_generic_signature_t signature)
  98 {
  99         ptrauth_generic_signature_t calculated_signature = 0;
 100
 101         if (ptr == NULL) {
 102                 if (flags & PTRAUTH_NON_NULL) {
 103                         panic("ptrauth_utils_auth_blob_generic: ptr must not be NULL");
 104                 } else {
 105                         return;
 106                 }
 107         }
 108
 109         if ((calculated_signature = ptrauth_utils_sign_blob_generic(ptr, len_bytes, data, flags)) == signature) {
 110                 return;
 111         } else {
 112                 panic("signature mismatch for %lu bytes at %p, calculated %lx vs %lx", len_bytes,
 113                     ptr,
 114                     calculated_signature,
 115                     signature);
 116         }
 117 }
 118
 119 #endif //!ptrauth_calls