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Fix PAE DTB detection rejecting valid 4-entry PDPTs #1993

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Fix PAE DTB detection rejecting valid 4-entry PDPTs #1993

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16 changes: 10 additions & 6 deletions volatility3/framework/automagic/windows.py
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Original file line number Diff line number Diff line change
Expand Up @@ -317,13 +317,12 @@ def get_max_pointer(page_table, test, ptr_size: int):
)
return max_ptr

def page_table_is_dummy(page_table, ptr_size: int):
"""Verify that a page table has at least 12 valid pointers"""
def page_table_is_dummy(page_table, ptr_size: int, minimum: int = 10):
"""Verify that a page table has at least `minimum` valid pointers"""
valid_pointers = 0
for _ in get_valid_page_table_pointers(page_table, ptr_size):
valid_pointers += 1
# 10 is an arbitrary constant
if valid_pointers >= 10:
if valid_pointers >= minimum:
# Do not consume the entire generator to enhance performance
return False
vollog.debug(f"Found {valid_pointers} valid pointers")
Expand All @@ -337,10 +336,15 @@ def page_table_is_dummy(page_table, ptr_size: int):
# Turn the page tables into integers and find the largest one
page_table = base_layer.read(page_map_offset, 0x1000)
ptr_size = struct.calcsize(test.ptr_struct)
# The PAE top-level table (the PDPT pointed to by CR3) legitimately
# contains only four entries, so the dummy-table heuristic - aimed at
# modern x64 stub tables that hold ~2 entries - must use a lower
# threshold for PAE or it would discard every valid PAE DTB.
minimum_valid = 4 if test.layer_type is intel.WindowsIntelPAE else 10
# Modern windows can have a dummy page table with only about 2 entries, so sanity check
if page_table_is_dummy(page_table, ptr_size):
if page_table_is_dummy(page_table, ptr_size, minimum_valid):
vollog.debug(
f"DTB {page_map_offset:x} contains less than 12 valid pointers, ignoring"
f"DTB {page_map_offset:x} contains less than {minimum_valid} valid pointers, ignoring"
)
continue

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