Security/libsecurity_codesigning/lib/cskernel.cpp

   1 /*
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  10  * http://www.opensource.apple.com/apsl/ and read it before using this
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  23
  24 //
  25 // cskernel - Kernel implementation of the Code Signing Host Interface.
  26 //
  27 // The kernel host currently supports only UNIX processes as guests.
  28 // It tracks then by their pid. Perhaps one day we'll get a more stable
  29 // means of tracking processes that doesn't involve reusing identifiers.
  30 //
  31 // The kernel host could represent non-process guests one day. One candidate
  32 // are Kernel Extensions.
  33 //
  34 #include "cskernel.h"
  35 #include "csprocess.h"
  36 #include "kerneldiskrep.h"
  37 #include "machorep.h"
  38 #include <libproc.h>
  39 #include <sys/codesign.h>
  40 #include <sys/param.h>  // MAXPATHLEN
  41
  42 namespace Security {
  43 namespace CodeSigning {
  44
  45
  46 //
  47 // The running-kernel singletons
  48 //
  49 ModuleNexus<KernelCode::Globals> KernelCode::globals;
  50
  51 KernelCode::Globals::Globals()
  52 {
  53         code = new KernelCode;
  54         staticCode = new KernelStaticCode;
  55 }
  56
  57 KernelCode::KernelCode()
  58         : SecCode(NULL)
  59 {
  60 }
  61
  62 KernelStaticCode::KernelStaticCode()
  63         : SecStaticCode(new KernelDiskRep())
  64 {
  65 }
  66
  67
  68 //
  69 // Identify our guests (UNIX processes) by attribute.
  70 // The only supported lookup attribute is currently the pid. (We could support
  71 // task ports, but those can easily be mapped to pids.)
  72 // Note that we don't actually validate the pid here; if it's invalid, we'll notice
  73 // when we try to ask the kernel about it later.
  74 //
  75 SecCode *KernelCode::locateGuest(CFDictionaryRef attributes)
  76 {
  77         if (CFTypeRef attr = CFDictionaryGetValue(attributes, kSecGuestAttributePid)) {
  78                 RefPointer<PidDiskRep> diskRep = NULL;
  79
  80                 if (CFGetTypeID(attr) != CFNumberGetTypeID())
  81                         MacOSError::throwMe(errSecCSInvalidAttributeValues);
  82
  83                 pid_t pid = cfNumber<pid_t>(CFNumberRef(attr));
  84
  85                 if (CFDictionaryGetValue(attributes, kSecGuestAttributeDynamicCode) != NULL) {
  86                         CFDataRef infoPlist = (CFDataRef)CFDictionaryGetValue(attributes, kSecGuestAttributeDynamicCodeInfoPlist);
  87                         if (infoPlist && CFGetTypeID(infoPlist) != CFDataGetTypeID())
  88                                 MacOSError::throwMe(errSecCSInvalidAttributeValues);
  89
  90                                                 try {
  91                                 diskRep = new PidDiskRep(pid, infoPlist);
  92                                                 } catch (...) { }
  93                 }
  94                 return (new ProcessCode(cfNumber<pid_t>(CFNumberRef(attr)), diskRep))->retain();
  95         } else
  96                 MacOSError::throwMe(errSecCSUnsupportedGuestAttributes);
  97 }
  98
  99
 100 //
 101 // We map guests to disk by calling a kernel service.
 102 // It is here that we verify that our user-space concept of the code identity
 103 // matches the kernel's idea (to defeat just-in-time switching attacks).
 104 //
 105 SecStaticCode *KernelCode::identifyGuest(SecCode *iguest, CFDataRef *cdhash)
 106 {
 107         if (ProcessCode *guest = dynamic_cast<ProcessCode *>(iguest)) {
 108
 109                 if (guest->pidBased()) {
 110
 111                         SecPointer<SecStaticCode> code = new ProcessDynamicCode(guest);
 112
 113                         SHA1::Digest kernelHash;
 114                         MacOSError::check(::csops(guest->pid(), CS_OPS_CDHASH, kernelHash, sizeof(kernelHash)));
 115                         *cdhash = makeCFData(kernelHash, sizeof(kernelHash));
 116
 117                         return code.yield();
 118                 }
 119
 120                 char path[2 * MAXPATHLEN];      // reasonable upper limit
 121                 if (::proc_pidpath(guest->pid(), path, sizeof(path))) {
 122                         off_t offset;
 123                         csops(guest, CS_OPS_PIDOFFSET, &offset, sizeof(offset));
 124                         SecPointer<SecStaticCode> code = new ProcessStaticCode(DiskRep::bestGuess(path, (size_t)offset));
 125                         CODESIGN_GUEST_IDENTIFY_PROCESS(guest, guest->pid(), code);
 126                         if (cdhash) {
 127                                 SHA1::Digest kernelHash;
 128                                 if (::csops(guest->pid(), CS_OPS_CDHASH, kernelHash, sizeof(kernelHash)) == -1)
 129                                         switch (errno) {
 130                                         case EBADEXEC:          // means "no CodeDirectory hash for this program"
 131                                                 *cdhash = NULL;
 132                                                 break;
 133                                         case ESRCH:
 134                                                 MacOSError::throwMe(errSecCSNoSuchCode);
 135                                         default:
 136                                                 UnixError::throwMe();
 137                                         }
 138                                 else    // succeeded
 139                                         *cdhash = makeCFData(kernelHash, sizeof(kernelHash));
 140                                 CODESIGN_GUEST_CDHASH_PROCESS(guest, kernelHash, sizeof(kernelHash));
 141                         }
 142                         return code.yield();
 143                 } else
 144                         UnixError::throwMe();
 145         }
 146         MacOSError::throwMe(errSecCSNoSuchCode);
 147 }
 148
 149
 150 //
 151 // We obtain the guest's status by asking the kernel
 152 //
 153 SecCodeStatus KernelCode::getGuestStatus(SecCode *iguest)
 154 {
 155         if (ProcessCode *guest = dynamic_cast<ProcessCode *>(iguest)) {
 156                 uint32_t pFlags;
 157                 csops(guest, CS_OPS_STATUS, &pFlags);
 158                 secdebug("kcode", "guest %p(%d) kernel status 0x%x", guest, guest->pid(), pFlags);
 159                 return pFlags;
 160         } else
 161                 MacOSError::throwMe(errSecCSNoSuchCode);
 162 }
 163
 164
 165 //
 166 // We tell the kernel to make status changes
 167 //
 168 void KernelCode::changeGuestStatus(SecCode *iguest, SecCodeStatusOperation operation, CFDictionaryRef arguments)
 169 {
 170         if (ProcessCode *guest = dynamic_cast<ProcessCode *>(iguest))
 171                 switch (operation) {
 172                 case kSecCodeOperationNull:
 173                         break;
 174                 case kSecCodeOperationInvalidate:
 175                         csops(guest, CS_OPS_MARKINVALID);
 176                         break;
 177                 case kSecCodeOperationSetHard:
 178                         csops(guest, CS_OPS_MARKHARD);
 179                         break;
 180                 case kSecCodeOperationSetKill:
 181                         csops(guest, CS_OPS_MARKKILL);
 182                         break;
 183                 default:
 184                         MacOSError::throwMe(errSecCSUnimplemented);
 185                 }
 186         else
 187                 MacOSError::throwMe(errSecCSNoSuchCode);
 188 }
 189
 190
 191 //
 192 // The StaticCode for the running kernel is explicit.
 193 // We can't ask our own host for it, naturally.
 194 //
 195 void KernelCode::identify()
 196 {
 197         mStaticCode.take(globals().staticCode->retain());
 198         // the kernel isn't currently signed, so we don't get a cdHash for it
 199 }
 200
 201
 202 //
 203 // Interface to kernel csops() system call.
 204 //
 205 void KernelCode::csops(ProcessCode *proc, unsigned int op, void *addr, size_t length)
 206 {
 207         if (::csops(proc->pid(), op, addr, length) == -1) {
 208                 switch (errno) {
 209                 case ESRCH:
 210                         MacOSError::throwMe(errSecCSNoSuchCode);
 211                 default:
 212                         UnixError::throwMe();
 213                 }
 214         }
 215 }
 216
 217
 218 } // CodeSigning
 219 } // Security