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Layers: Make the low-stub method less brittle #1581

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Merged
ikelos merged 1 commit into from
Jan 27, 2025
+34 −30
Merged

Layers: Make the low-stub method less brittle #1581

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64 changes: 34 additions & 30 deletions volatility3/framework/automagic/pdbscan.py
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Original file line number Diff line number Diff line change
Expand Up @@ -392,38 +392,42 @@ def method_low_stub_offset(
# Try locating kernel base via x64 Low Stub in lower 1MB starting from second page (4KB)
# If "Discard Low Memory" setting is disabled in BIOS, the Low Stub may be at the third/fourth or further pages
for offset in range(0x1000, 0x100000, 0x1000):
jmp_and_completion_values = int.from_bytes(
physical_layer.read(offset, 0x8), "little"
)
if (
0xFFFFFFFFFFFF00FF & jmp_and_completion_values
!= constants.windows.JMP_AND_COMPLETION_SIGNATURE
):
continue
cr3_value = int.from_bytes(
physical_layer.read(
offset + constants.windows.PROCESSOR_START_BLOCK_CR3_OFFSET, 0x8
),
"little",
)
try:
jmp_and_completion_values = int.from_bytes(
physical_layer.read(offset, 0x8), "little"
)
if (
0xFFFFFFFFFFFF00FF & jmp_and_completion_values
!= constants.windows.JMP_AND_COMPLETION_SIGNATURE
):
continue
cr3_value = int.from_bytes(
physical_layer.read(
offset + constants.windows.PROCESSOR_START_BLOCK_CR3_OFFSET, 0x8
),
"little",
)

# Compare previously observed valid page table address that's stored in vlayer._initial_entry
# with PROCESSOR_START_BLOCK->ProcessorState->SpecialRegisters->Cr3
# which was observed to be an invalid page address, so add 1 (to make it valid too)
if (cr3_value + 1) != vlayer._initial_entry:
continue
potential_kernel_hint = int.from_bytes(
physical_layer.read(
offset + constants.windows.PROCESSOR_START_BLOCK_LM_TARGET_OFFSET,
0x8,
),
"little",
)
if 0x3 & potential_kernel_hint:
# Compare previously observed valid page table address that's stored in vlayer._initial_entry
# with PROCESSOR_START_BLOCK->ProcessorState->SpecialRegisters->Cr3
# which was observed to be an invalid page address, so add 1 (to make it valid too)
if (cr3_value + 1) != vlayer._initial_entry:
continue
potential_kernel_hint = int.from_bytes(
physical_layer.read(
offset
+ constants.windows.PROCESSOR_START_BLOCK_LM_TARGET_OFFSET,
0x8,
),
"little",
)
if 0x3 & potential_kernel_hint:
continue
kernel_hint = potential_kernel_hint & 0xFFFFFFFFFFFF
kernel_base = kernel_hint & (~0x1FFFFF) & 0xFFFFFFFFFFFF
break
except exceptions.InvalidAddressException:
continue
kernel_hint = potential_kernel_hint & 0xFFFFFFFFFFFF
kernel_base = kernel_hint & (~0x1FFFFF) & 0xFFFFFFFFFFFF
break

if kernel_base:
# Scanning 32mb in 2mb chunks for the 'ntoskrnl' base address
Expand Down
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