scripts/dump-guest-memory.py

   1 """
   2 This python script adds a new gdb command, "dump-guest-memory". It
   3 should be loaded with "source dump-guest-memory.py" at the (gdb)
   4 prompt.
   5
   6 Copyright (C) 2013, Red Hat, Inc.
   7
   8 Authors:
   9    Laszlo Ersek <lersek@redhat.com>
  10    Janosch Frank <frankja@linux.vnet.ibm.com>
  11
  12 This work is licensed under the terms of the GNU GPL, version 2 or later. See
  13 the COPYING file in the top-level directory.
  14 """
  15
  16 import ctypes
  17
  18 UINTPTR_T = gdb.lookup_type("uintptr_t")
  19
  20 TARGET_PAGE_SIZE = 0x1000
  21 TARGET_PAGE_MASK = 0xFFFFFFFFFFFFF000
  22
  23 # Special value for e_phnum. This indicates that the real number of
  24 # program headers is too large to fit into e_phnum. Instead the real
  25 # value is in the field sh_info of section 0.
  26 PN_XNUM = 0xFFFF
  27
  28 EV_CURRENT = 1
  29
  30 ELFCLASS32 = 1
  31 ELFCLASS64 = 2
  32
  33 ELFDATA2LSB = 1
  34 ELFDATA2MSB = 2
  35
  36 ET_CORE = 4
  37
  38 PT_LOAD = 1
  39 PT_NOTE = 4
  40
  41 EM_386 = 3
  42 EM_PPC = 20
  43 EM_PPC64 = 21
  44 EM_S390 = 22
  45 EM_AARCH = 183
  46 EM_X86_64 = 62
  47
  48 class ELF(object):
  49     """Representation of a ELF file."""
  50
  51     def __init__(self, arch):
  52         self.ehdr = None
  53         self.notes = []
  54         self.segments = []
  55         self.notes_size = 0
  56         self.endianness = None
  57         self.elfclass = ELFCLASS64
  58
  59         if arch == 'aarch64-le':
  60             self.endianness = ELFDATA2LSB
  61             self.elfclass = ELFCLASS64
  62             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  63             self.ehdr.e_machine = EM_AARCH
  64
  65         elif arch == 'aarch64-be':
  66             self.endianness = ELFDATA2MSB
  67             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  68             self.ehdr.e_machine = EM_AARCH
  69
  70         elif arch == 'X86_64':
  71             self.endianness = ELFDATA2LSB
  72             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  73             self.ehdr.e_machine = EM_X86_64
  74
  75         elif arch == '386':
  76             self.endianness = ELFDATA2LSB
  77             self.elfclass = ELFCLASS32
  78             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  79             self.ehdr.e_machine = EM_386
  80
  81         elif arch == 's390':
  82             self.endianness = ELFDATA2MSB
  83             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  84             self.ehdr.e_machine = EM_S390
  85
  86         elif arch == 'ppc64-le':
  87             self.endianness = ELFDATA2LSB
  88             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  89             self.ehdr.e_machine = EM_PPC64
  90
  91         elif arch == 'ppc64-be':
  92             self.endianness = ELFDATA2MSB
  93             self.ehdr = get_arch_ehdr(self.endianness, self.elfclass)
  94             self.ehdr.e_machine = EM_PPC64
  95
  96         else:
  97             raise gdb.GdbError("No valid arch type specified.\n"
  98                                "Currently supported types:\n"
  99                                "aarch64-be, aarch64-le, X86_64, 386, s390, "
 100                                "ppc64-be, ppc64-le")
 101
 102         self.add_segment(PT_NOTE, 0, 0)
 103
 104     def add_note(self, n_name, n_desc, n_type):
 105         """Adds a note to the ELF."""
 106
 107         note = get_arch_note(self.endianness, len(n_name), len(n_desc))
 108         note.n_namesz = len(n_name) + 1
 109         note.n_descsz = len(n_desc)
 110         note.n_name = n_name.encode()
 111         note.n_type = n_type
 112
 113         # Desc needs to be 4 byte aligned (although the 64bit spec
 114         # specifies 8 byte). When defining n_desc as uint32 it will be
 115         # automatically aligned but we need the memmove to copy the
 116         # string into it.
 117         ctypes.memmove(note.n_desc, n_desc.encode(), len(n_desc))
 118
 119         self.notes.append(note)
 120         self.segments[0].p_filesz += ctypes.sizeof(note)
 121         self.segments[0].p_memsz += ctypes.sizeof(note)
 122
 123     def add_segment(self, p_type, p_paddr, p_size):
 124         """Adds a segment to the elf."""
 125
 126         phdr = get_arch_phdr(self.endianness, self.elfclass)
 127         phdr.p_type = p_type
 128         phdr.p_paddr = p_paddr
 129         phdr.p_filesz = p_size
 130         phdr.p_memsz = p_size
 131         self.segments.append(phdr)
 132         self.ehdr.e_phnum += 1
 133
 134     def to_file(self, elf_file):
 135         """Writes all ELF structures to the the passed file.
 136
 137         Structure:
 138         Ehdr
 139         Segment 0:PT_NOTE
 140         Segment 1:PT_LOAD
 141         Segment N:PT_LOAD
 142         Note    0..N
 143         Dump contents
 144         """
 145         elf_file.write(self.ehdr)
 146         off = ctypes.sizeof(self.ehdr) + \
 147               len(self.segments) * ctypes.sizeof(self.segments[0])
 148
 149         for phdr in self.segments:
 150             phdr.p_offset = off
 151             elf_file.write(phdr)
 152             off += phdr.p_filesz
 153
 154         for note in self.notes:
 155             elf_file.write(note)
 156
 157
 158 def get_arch_note(endianness, len_name, len_desc):
 159     """Returns a Note class with the specified endianness."""
 160
 161     if endianness == ELFDATA2LSB:
 162         superclass = ctypes.LittleEndianStructure
 163     else:
 164         superclass = ctypes.BigEndianStructure
 165
 166     len_name = len_name + 1
 167
 168     class Note(superclass):
 169         """Represents an ELF note, includes the content."""
 170
 171         _fields_ = [("n_namesz", ctypes.c_uint32),
 172                     ("n_descsz", ctypes.c_uint32),
 173                     ("n_type", ctypes.c_uint32),
 174                     ("n_name", ctypes.c_char * len_name),
 175                     ("n_desc", ctypes.c_uint32 * ((len_desc + 3) // 4))]
 176     return Note()
 177
 178
 179 class Ident(ctypes.Structure):
 180     """Represents the ELF ident array in the ehdr structure."""
 181
 182     _fields_ = [('ei_mag0', ctypes.c_ubyte),
 183                 ('ei_mag1', ctypes.c_ubyte),
 184                 ('ei_mag2', ctypes.c_ubyte),
 185                 ('ei_mag3', ctypes.c_ubyte),
 186                 ('ei_class', ctypes.c_ubyte),
 187                 ('ei_data', ctypes.c_ubyte),
 188                 ('ei_version', ctypes.c_ubyte),
 189                 ('ei_osabi', ctypes.c_ubyte),
 190                 ('ei_abiversion', ctypes.c_ubyte),
 191                 ('ei_pad', ctypes.c_ubyte * 7)]
 192
 193     def __init__(self, endianness, elfclass):
 194         self.ei_mag0 = 0x7F
 195         self.ei_mag1 = ord('E')
 196         self.ei_mag2 = ord('L')
 197         self.ei_mag3 = ord('F')
 198         self.ei_class = elfclass
 199         self.ei_data = endianness
 200         self.ei_version = EV_CURRENT
 201
 202
 203 def get_arch_ehdr(endianness, elfclass):
 204     """Returns a EHDR64 class with the specified endianness."""
 205
 206     if endianness == ELFDATA2LSB:
 207         superclass = ctypes.LittleEndianStructure
 208     else:
 209         superclass = ctypes.BigEndianStructure
 210
 211     class EHDR64(superclass):
 212         """Represents the 64 bit ELF header struct."""
 213
 214         _fields_ = [('e_ident', Ident),
 215                     ('e_type', ctypes.c_uint16),
 216                     ('e_machine', ctypes.c_uint16),
 217                     ('e_version', ctypes.c_uint32),
 218                     ('e_entry', ctypes.c_uint64),
 219                     ('e_phoff', ctypes.c_uint64),
 220                     ('e_shoff', ctypes.c_uint64),
 221                     ('e_flags', ctypes.c_uint32),
 222                     ('e_ehsize', ctypes.c_uint16),
 223                     ('e_phentsize', ctypes.c_uint16),
 224                     ('e_phnum', ctypes.c_uint16),
 225                     ('e_shentsize', ctypes.c_uint16),
 226                     ('e_shnum', ctypes.c_uint16),
 227                     ('e_shstrndx', ctypes.c_uint16)]
 228
 229         def __init__(self):
 230             super(superclass, self).__init__()
 231             self.e_ident = Ident(endianness, elfclass)
 232             self.e_type = ET_CORE
 233             self.e_version = EV_CURRENT
 234             self.e_ehsize = ctypes.sizeof(self)
 235             self.e_phoff = ctypes.sizeof(self)
 236             self.e_phentsize = ctypes.sizeof(get_arch_phdr(endianness, elfclass))
 237             self.e_phnum = 0
 238
 239
 240     class EHDR32(superclass):
 241         """Represents the 32 bit ELF header struct."""
 242
 243         _fields_ = [('e_ident', Ident),
 244                     ('e_type', ctypes.c_uint16),
 245                     ('e_machine', ctypes.c_uint16),
 246                     ('e_version', ctypes.c_uint32),
 247                     ('e_entry', ctypes.c_uint32),
 248                     ('e_phoff', ctypes.c_uint32),
 249                     ('e_shoff', ctypes.c_uint32),
 250                     ('e_flags', ctypes.c_uint32),
 251                     ('e_ehsize', ctypes.c_uint16),
 252                     ('e_phentsize', ctypes.c_uint16),
 253                     ('e_phnum', ctypes.c_uint16),
 254                     ('e_shentsize', ctypes.c_uint16),
 255                     ('e_shnum', ctypes.c_uint16),
 256                     ('e_shstrndx', ctypes.c_uint16)]
 257
 258         def __init__(self):
 259             super(superclass, self).__init__()
 260             self.e_ident = Ident(endianness, elfclass)
 261             self.e_type = ET_CORE
 262             self.e_version = EV_CURRENT
 263             self.e_ehsize = ctypes.sizeof(self)
 264             self.e_phoff = ctypes.sizeof(self)
 265             self.e_phentsize = ctypes.sizeof(get_arch_phdr(endianness, elfclass))
 266             self.e_phnum = 0
 267
 268     # End get_arch_ehdr
 269     if elfclass == ELFCLASS64:
 270         return EHDR64()
 271     else:
 272         return EHDR32()
 273
 274
 275 def get_arch_phdr(endianness, elfclass):
 276     """Returns a 32 or 64 bit PHDR class with the specified endianness."""
 277
 278     if endianness == ELFDATA2LSB:
 279         superclass = ctypes.LittleEndianStructure
 280     else:
 281         superclass = ctypes.BigEndianStructure
 282
 283     class PHDR64(superclass):
 284         """Represents the 64 bit ELF program header struct."""
 285
 286         _fields_ = [('p_type', ctypes.c_uint32),
 287                     ('p_flags', ctypes.c_uint32),
 288                     ('p_offset', ctypes.c_uint64),
 289                     ('p_vaddr', ctypes.c_uint64),
 290                     ('p_paddr', ctypes.c_uint64),
 291                     ('p_filesz', ctypes.c_uint64),
 292                     ('p_memsz', ctypes.c_uint64),
 293                     ('p_align', ctypes.c_uint64)]
 294
 295     class PHDR32(superclass):
 296         """Represents the 32 bit ELF program header struct."""
 297
 298         _fields_ = [('p_type', ctypes.c_uint32),
 299                     ('p_offset', ctypes.c_uint32),
 300                     ('p_vaddr', ctypes.c_uint32),
 301                     ('p_paddr', ctypes.c_uint32),
 302                     ('p_filesz', ctypes.c_uint32),
 303                     ('p_memsz', ctypes.c_uint32),
 304                     ('p_flags', ctypes.c_uint32),
 305                     ('p_align', ctypes.c_uint32)]
 306
 307     # End get_arch_phdr
 308     if elfclass == ELFCLASS64:
 309         return PHDR64()
 310     else:
 311         return PHDR32()
 312
 313
 314 def int128_get64(val):
 315     """Returns low 64bit part of Int128 struct."""
 316
 317     assert val["hi"] == 0
 318     return val["lo"]
 319
 320
 321 def qlist_foreach(head, field_str):
 322     """Generator for qlists."""
 323
 324     var_p = head["lh_first"]
 325     while var_p != 0:
 326         var = var_p.dereference()
 327         var_p = var[field_str]["le_next"]
 328         yield var
 329
 330
 331 def qemu_map_ram_ptr(block, offset):
 332     """Returns qemu vaddr for given guest physical address."""
 333
 334     return block["host"] + offset
 335
 336
 337 def memory_region_get_ram_ptr(memory_region):
 338     if memory_region["alias"] != 0:
 339         return (memory_region_get_ram_ptr(memory_region["alias"].dereference())
 340                 + memory_region["alias_offset"])
 341
 342     return qemu_map_ram_ptr(memory_region["ram_block"], 0)
 343
 344
 345 def get_guest_phys_blocks():
 346     """Returns a list of ram blocks.
 347
 348     Each block entry contains:
 349     'target_start': guest block phys start address
 350     'target_end':   guest block phys end address
 351     'host_addr':    qemu vaddr of the block's start
 352     """
 353
 354     guest_phys_blocks = []
 355
 356     print("guest RAM blocks:")
 357     print("target_start     target_end       host_addr        message "
 358           "count")
 359     print("---------------- ---------------- ---------------- ------- "
 360           "-----")
 361
 362     current_map_p = gdb.parse_and_eval("address_space_memory.current_map")
 363     current_map = current_map_p.dereference()
 364
 365     # Conversion to int is needed for python 3
 366     # compatibility. Otherwise range doesn't cast the value itself and
 367     # breaks.
 368     for cur in range(int(current_map["nr"])):
 369         flat_range = (current_map["ranges"] + cur).dereference()
 370         memory_region = flat_range["mr"].dereference()
 371
 372         # we only care about RAM
 373         if not memory_region["ram"]:
 374             continue
 375
 376         section_size = int128_get64(flat_range["addr"]["size"])
 377         target_start = int128_get64(flat_range["addr"]["start"])
 378         target_end = target_start + section_size
 379         host_addr = (memory_region_get_ram_ptr(memory_region)
 380                      + flat_range["offset_in_region"])
 381         predecessor = None
 382
 383         # find continuity in guest physical address space
 384         if len(guest_phys_blocks) > 0:
 385             predecessor = guest_phys_blocks[-1]
 386             predecessor_size = (predecessor["target_end"] -
 387                                 predecessor["target_start"])
 388
 389             # the memory API guarantees monotonically increasing
 390             # traversal
 391             assert predecessor["target_end"] <= target_start
 392
 393             # we want continuity in both guest-physical and
 394             # host-virtual memory
 395             if (predecessor["target_end"] < target_start or
 396                 predecessor["host_addr"] + predecessor_size != host_addr):
 397                 predecessor = None
 398
 399         if predecessor is None:
 400             # isolated mapping, add it to the list
 401             guest_phys_blocks.append({"target_start": target_start,
 402                                       "target_end":   target_end,
 403                                       "host_addr":    host_addr})
 404             message = "added"
 405         else:
 406             # expand predecessor until @target_end; predecessor's
 407             # start doesn't change
 408             predecessor["target_end"] = target_end
 409             message = "joined"
 410
 411         print("%016x %016x %016x %-7s %5u" %
 412               (target_start, target_end, host_addr.cast(UINTPTR_T),
 413                message, len(guest_phys_blocks)))
 414
 415     return guest_phys_blocks
 416
 417
 418 # The leading docstring doesn't have idiomatic Python formatting. It is
 419 # printed by gdb's "help" command (the first line is printed in the
 420 # "help data" summary), and it should match how other help texts look in
 421 # gdb.
 422 class DumpGuestMemory(gdb.Command):
 423     """Extract guest vmcore from qemu process coredump.
 424
 425 The two required arguments are FILE and ARCH:
 426 FILE identifies the target file to write the guest vmcore to.
 427 ARCH specifies the architecture for which the core will be generated.
 428
 429 This GDB command reimplements the dump-guest-memory QMP command in
 430 python, using the representation of guest memory as captured in the qemu
 431 coredump. The qemu process that has been dumped must have had the
 432 command line option "-machine dump-guest-core=on" which is the default.
 433
 434 For simplicity, the "paging", "begin" and "end" parameters of the QMP
 435 command are not supported -- no attempt is made to get the guest's
 436 internal paging structures (ie. paging=false is hard-wired), and guest
 437 memory is always fully dumped.
 438
 439 Currently aarch64-be, aarch64-le, X86_64, 386, s390, ppc64-be,
 440 ppc64-le guests are supported.
 441
 442 The CORE/NT_PRSTATUS and QEMU notes (that is, the VCPUs' statuses) are
 443 not written to the vmcore. Preparing these would require context that is
 444 only present in the KVM host kernel module when the guest is alive. A
 445 fake ELF note is written instead, only to keep the ELF parser of "crash"
 446 happy.
 447
 448 Dependent on how busted the qemu process was at the time of the
 449 coredump, this command might produce unpredictable results. If qemu
 450 deliberately called abort(), or it was dumped in response to a signal at
 451 a halfway fortunate point, then its coredump should be in reasonable
 452 shape and this command should mostly work."""
 453
 454     def __init__(self):
 455         super(DumpGuestMemory, self).__init__("dump-guest-memory",
 456                                               gdb.COMMAND_DATA,
 457                                               gdb.COMPLETE_FILENAME)
 458         self.elf = None
 459         self.guest_phys_blocks = None
 460
 461     def dump_init(self, vmcore):
 462         """Prepares and writes ELF structures to core file."""
 463
 464         # Needed to make crash happy, data for more useful notes is
 465         # not available in a qemu core.
 466         self.elf.add_note("NONE", "EMPTY", 0)
 467
 468         # We should never reach PN_XNUM for paging=false dumps,
 469         # there's just a handful of discontiguous ranges after
 470         # merging.
 471         # The constant is needed to account for the PT_NOTE segment.
 472         phdr_num = len(self.guest_phys_blocks) + 1
 473         assert phdr_num < PN_XNUM
 474
 475         for block in self.guest_phys_blocks:
 476             block_size = block["target_end"] - block["target_start"]
 477             self.elf.add_segment(PT_LOAD, block["target_start"], block_size)
 478
 479         self.elf.to_file(vmcore)
 480
 481     def dump_iterate(self, vmcore):
 482         """Writes guest core to file."""
 483
 484         qemu_core = gdb.inferiors()[0]
 485         for block in self.guest_phys_blocks:
 486             cur = block["host_addr"]
 487             left = block["target_end"] - block["target_start"]
 488             print("dumping range at %016x for length %016x" %
 489                   (cur.cast(UINTPTR_T), left))
 490
 491             while left > 0:
 492                 chunk_size = min(TARGET_PAGE_SIZE, left)
 493                 chunk = qemu_core.read_memory(cur, chunk_size)
 494                 vmcore.write(chunk)
 495                 cur += chunk_size
 496                 left -= chunk_size
 497
 498     def invoke(self, args, from_tty):
 499         """Handles command invocation from gdb."""
 500
 501         # Unwittingly pressing the Enter key after the command should
 502         # not dump the same multi-gig coredump to the same file.
 503         self.dont_repeat()
 504
 505         argv = gdb.string_to_argv(args)
 506         if len(argv) != 2:
 507             raise gdb.GdbError("usage: dump-guest-memory FILE ARCH")
 508
 509         self.elf = ELF(argv[1])
 510         self.guest_phys_blocks = get_guest_phys_blocks()
 511
 512         with open(argv[0], "wb") as vmcore:
 513             self.dump_init(vmcore)
 514             self.dump_iterate(vmcore)
 515
 516 DumpGuestMemory()