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     try:
 318         assert val["hi"] == 0
 319         return val["lo"]
 320     except gdb.error:
 321         u64t = gdb.lookup_type('uint64_t').array(2)
 322         u64 = val.cast(u64t)
 323         if sys.byteorder == 'little':
 324             assert u64[1] == 0
 325             return u64[0]
 326         else:
 327             assert u64[0] == 0
 328             return u64[1]
 329
 330
 331 def qlist_foreach(head, field_str):
 332     """Generator for qlists."""
 333
 334     var_p = head["lh_first"]
 335     while var_p != 0:
 336         var = var_p.dereference()
 337         var_p = var[field_str]["le_next"]
 338         yield var
 339
 340
 341 def qemu_map_ram_ptr(block, offset):
 342     """Returns qemu vaddr for given guest physical address."""
 343
 344     return block["host"] + offset
 345
 346
 347 def memory_region_get_ram_ptr(memory_region):
 348     if memory_region["alias"] != 0:
 349         return (memory_region_get_ram_ptr(memory_region["alias"].dereference())
 350                 + memory_region["alias_offset"])
 351
 352     return qemu_map_ram_ptr(memory_region["ram_block"], 0)
 353
 354
 355 def get_guest_phys_blocks():
 356     """Returns a list of ram blocks.
 357
 358     Each block entry contains:
 359     'target_start': guest block phys start address
 360     'target_end':   guest block phys end address
 361     'host_addr':    qemu vaddr of the block's start
 362     """
 363
 364     guest_phys_blocks = []
 365
 366     print("guest RAM blocks:")
 367     print("target_start     target_end       host_addr        message "
 368           "count")
 369     print("---------------- ---------------- ---------------- ------- "
 370           "-----")
 371
 372     current_map_p = gdb.parse_and_eval("address_space_memory.current_map")
 373     current_map = current_map_p.dereference()
 374
 375     # Conversion to int is needed for python 3
 376     # compatibility. Otherwise range doesn't cast the value itself and
 377     # breaks.
 378     for cur in range(int(current_map["nr"])):
 379         flat_range = (current_map["ranges"] + cur).dereference()
 380         memory_region = flat_range["mr"].dereference()
 381
 382         # we only care about RAM
 383         if not memory_region["ram"]:
 384             continue
 385
 386         section_size = int128_get64(flat_range["addr"]["size"])
 387         target_start = int128_get64(flat_range["addr"]["start"])
 388         target_end = target_start + section_size
 389         host_addr = (memory_region_get_ram_ptr(memory_region)
 390                      + flat_range["offset_in_region"])
 391         predecessor = None
 392
 393         # find continuity in guest physical address space
 394         if len(guest_phys_blocks) > 0:
 395             predecessor = guest_phys_blocks[-1]
 396             predecessor_size = (predecessor["target_end"] -
 397                                 predecessor["target_start"])
 398
 399             # the memory API guarantees monotonically increasing
 400             # traversal
 401             assert predecessor["target_end"] <= target_start
 402
 403             # we want continuity in both guest-physical and
 404             # host-virtual memory
 405             if (predecessor["target_end"] < target_start or
 406                 predecessor["host_addr"] + predecessor_size != host_addr):
 407                 predecessor = None
 408
 409         if predecessor is None:
 410             # isolated mapping, add it to the list
 411             guest_phys_blocks.append({"target_start": target_start,
 412                                       "target_end":   target_end,
 413                                       "host_addr":    host_addr})
 414             message = "added"
 415         else:
 416             # expand predecessor until @target_end; predecessor's
 417             # start doesn't change
 418             predecessor["target_end"] = target_end
 419             message = "joined"
 420
 421         print("%016x %016x %016x %-7s %5u" %
 422               (target_start, target_end, host_addr.cast(UINTPTR_T),
 423                message, len(guest_phys_blocks)))
 424
 425     return guest_phys_blocks
 426
 427
 428 # The leading docstring doesn't have idiomatic Python formatting. It is
 429 # printed by gdb's "help" command (the first line is printed in the
 430 # "help data" summary), and it should match how other help texts look in
 431 # gdb.
 432 class DumpGuestMemory(gdb.Command):
 433     """Extract guest vmcore from qemu process coredump.
 434
 435 The two required arguments are FILE and ARCH:
 436 FILE identifies the target file to write the guest vmcore to.
 437 ARCH specifies the architecture for which the core will be generated.
 438
 439 This GDB command reimplements the dump-guest-memory QMP command in
 440 python, using the representation of guest memory as captured in the qemu
 441 coredump. The qemu process that has been dumped must have had the
 442 command line option "-machine dump-guest-core=on" which is the default.
 443
 444 For simplicity, the "paging", "begin" and "end" parameters of the QMP
 445 command are not supported -- no attempt is made to get the guest's
 446 internal paging structures (ie. paging=false is hard-wired), and guest
 447 memory is always fully dumped.
 448
 449 Currently aarch64-be, aarch64-le, X86_64, 386, s390, ppc64-be,
 450 ppc64-le guests are supported.
 451
 452 The CORE/NT_PRSTATUS and QEMU notes (that is, the VCPUs' statuses) are
 453 not written to the vmcore. Preparing these would require context that is
 454 only present in the KVM host kernel module when the guest is alive. A
 455 fake ELF note is written instead, only to keep the ELF parser of "crash"
 456 happy.
 457
 458 Dependent on how busted the qemu process was at the time of the
 459 coredump, this command might produce unpredictable results. If qemu
 460 deliberately called abort(), or it was dumped in response to a signal at
 461 a halfway fortunate point, then its coredump should be in reasonable
 462 shape and this command should mostly work."""
 463
 464     def __init__(self):
 465         super(DumpGuestMemory, self).__init__("dump-guest-memory",
 466                                               gdb.COMMAND_DATA,
 467                                               gdb.COMPLETE_FILENAME)
 468         self.elf = None
 469         self.guest_phys_blocks = None
 470
 471     def dump_init(self, vmcore):
 472         """Prepares and writes ELF structures to core file."""
 473
 474         # Needed to make crash happy, data for more useful notes is
 475         # not available in a qemu core.
 476         self.elf.add_note("NONE", "EMPTY", 0)
 477
 478         # We should never reach PN_XNUM for paging=false dumps,
 479         # there's just a handful of discontiguous ranges after
 480         # merging.
 481         # The constant is needed to account for the PT_NOTE segment.
 482         phdr_num = len(self.guest_phys_blocks) + 1
 483         assert phdr_num < PN_XNUM
 484
 485         for block in self.guest_phys_blocks:
 486             block_size = block["target_end"] - block["target_start"]
 487             self.elf.add_segment(PT_LOAD, block["target_start"], block_size)
 488
 489         self.elf.to_file(vmcore)
 490
 491     def dump_iterate(self, vmcore):
 492         """Writes guest core to file."""
 493
 494         qemu_core = gdb.inferiors()[0]
 495         for block in self.guest_phys_blocks:
 496             cur = block["host_addr"]
 497             left = block["target_end"] - block["target_start"]
 498             print("dumping range at %016x for length %016x" %
 499                   (cur.cast(UINTPTR_T), left))
 500
 501             while left > 0:
 502                 chunk_size = min(TARGET_PAGE_SIZE, left)
 503                 chunk = qemu_core.read_memory(cur, chunk_size)
 504                 vmcore.write(chunk)
 505                 cur += chunk_size
 506                 left -= chunk_size
 507
 508     def invoke(self, args, from_tty):
 509         """Handles command invocation from gdb."""
 510
 511         # Unwittingly pressing the Enter key after the command should
 512         # not dump the same multi-gig coredump to the same file.
 513         self.dont_repeat()
 514
 515         argv = gdb.string_to_argv(args)
 516         if len(argv) != 2:
 517             raise gdb.GdbError("usage: dump-guest-memory FILE ARCH")
 518
 519         self.elf = ELF(argv[1])
 520         self.guest_phys_blocks = get_guest_phys_blocks()
 521
 522         with open(argv[0], "wb") as vmcore:
 523             self.dump_init(vmcore)
 524             self.dump_iterate(vmcore)
 525
 526 DumpGuestMemory()