CODEWITHSUNDEEP
debuggingwindowkernelwindbg
user972014
user972014

Reputation: 3856

When Kernel Debugging - Find The Page Protection of a User Mode Address

While kernel debugging a windows (XP SP3) machine, I would like to find the page protection of a user mode address (actually just to check if it's a No-Execute page).

The extension !vprot (which does just that) doesn't work when kernel debugging.

I tried to change into this user mode address space (using '.process /i') and then call !pte on the address. But sometimes, the PTE entry is invalid, because it's paged out (I think).

Any suggestions?

Upvotes: 3

Views: 2909

Answers (1)

Neitsa
Neitsa

Reputation: 8166

You might try a combination of !vad and !address:

0: kd> !process 0 0 calc.exe
PROCESS 89e035f8  SessionId: 0  Cid: 021c    Peb: 7ffdd000  ParentCid: 00d4
    DirBase: 0aac0200  ObjectTable: e1f587a8  HandleCount:  44.
    Image: calc.exe

0: kd> .process /i 89e035f8

Using !vad:

3: kd> !vad 0x1000000
VAD     level      start      end    commit
89e02578 (-1)       1000     101e         3 Mapped  Exe  EXECUTE_WRITECOPY  \WINDOWS\system32\calc.exe
3: kd> !vad 0x1014000
VAD     level      start      end    commit
89e02578 (-1)       1000     101e         3 Mapped  Exe  EXECUTE_WRITECOPY  \WINDOWS\system32\calc.exe

The problem is that the !vad command gives you only the VAD (Virtual AQddress Descripptor) for the whole page range, which is more precisely the size of the VAD segment. Obviously the pages at 0x1000000 [PE Header] and 0x1014000 [.data section] haven't the same protections.

Using !address:

Note that the !address command will map a lot of things (including PTEs / PFNs and VADs):

3: kd> !address 0x1000000
Mapping user range ...
Mapping system range ...
Mapping page tables...
Mapping hyperspace...
Mapping HAL reserved range...
Mapping User Probe Area...
Mapping system shared page...
Mapping system cache working set...
Mapping loader mappings...
Mapping system PTEs...
Mapping system paged pool...
Mapping session space...
Mapping dynamic system space...
Mapping PFN database...
Mapping non paged pool...
Mapping VAD regions...
Mapping module regions...
Mapping process, thread, and stack regions...
Mapping system cache regions...

Use the -v and -map options:

3: kd> !address -v -map 0x1000000
PDE:    c0600040 [contains 20b9a867]

        Page Frame Number:  20b9a, at address: 00000000
        Page Location:      6 (ActiveAndValid)
        PTE Frame:          00020a98
        Attributes:         M:Modified,Cached
        Usage:              PTEs Process 89e035f8 [calc.exe], Entries:22

PTE:    c0008000 [contains 20d86025]

        Page Frame Number:  20d86, at address: 00000000
        Page Location:      6 (ActiveAndValid)
        PTE Frame:          00020384
        Attributes:         P:Prototype,M:Modified,Cached
        Usage:              MappedFile CA:8a1282e0 [\WINDOWS\system32\calc.exe]
        
Type:   Valid
Attrs:  Private,NormalPage,NotDirty,NotDirty1,Accessed,User,NotWritable,NotWriteThrough
PFN:    20d86

The Attrs output gives useful information. You might be able to use the !pte command at this point:

3: kd> !pte c0008000
                    VA 01000000
PDE at C0600040            PTE at C0008000
contains 0000000020B9A867  contains 0000000020D86025
pfn 20b9a     ---DA--UWEV  pfn 20d86     ----A--UREV

The output of !pte gives the PTE bits (to the right), here: ----A--UREV:

  • A: Accessed
  • U: User page
  • R: Read-only
  • E: Executable
  • V: Valid

Commands Documentation:

Hope that solve your problem.

Upvotes: 5

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