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Memory With WriteCombine Protection

 
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lylcheat
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PostPosted: Thu May 23, 2019 3:36 am    Post subject: Memory With WriteCombine Protection Reply with quote

I'm using systinternal's VMMap to list the memory map of a game client.
I notice that some memory regions have the protection attribute WriteCombine.
The msdn page https://docs.microsoft.com/en-us/windows/desktop/Memory/memory-protection-constants has some vague description and i guess that these writecombine pages should be some kind of shared video memory since I am using on-board display chip to play my game.

My question
1) what exactly are these pages with Writecombine protection flag?
2) how do we skip all these Writecombine pages when scanning, just like skipping non-writable pages[/url]



writecombine.png
 Description:
 Filesize:  103.68 KB
 Viewed:  2848 Time(s)

writecombine.png


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Dark Byte
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PostPosted: Thu May 23, 2019 4:17 am    Post subject: Reply with quote

write combine is a paging technique where some caching happens but writes get sent to the hardware immediately

Normally those memoryregions are marked as mem_mapped, and by default CE will skip that

check with memoryview-view-memory regions

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lylcheat
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PostPosted: Thu May 23, 2019 4:49 am    Post subject: Reply with quote

Dark Byte wrote:
write combine is a paging technique where some caching happens but writes get sent to the hardware immediately

Normally those memoryregions are marked as mem_mapped, and by default CE will skip that

check with memoryview-view-memory regions


Look at my printscreen, clearly both private memory MEM_PRIVATE (those in yellow) and sharable MEM_MAPPED (those in white, i.e. mem_mapped memory which are backed by paging file) can be Writecombine (it is a memory protection attribute not memory type). So skipping MEM_MAPPED seems not specific enough.
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Dark Byte
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PostPosted: Thu May 23, 2019 4:56 am    Post subject: Reply with quote

post a screenshot of CE's memory regions window
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lylcheat
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PostPosted: Fri May 24, 2019 3:18 am    Post subject: Reply with quote

Here is a screen shot using mame64 as the client (without anti-cheat issue).
CE doesn't seem to support WriteCombine flag at all. 0x16891000 is the mem page with WriteCombine flag as seen in VMMap, but it it not shown by CE. When scanning this memory page is treated as ordinary committed private page.



ce_mame.png
 Description:
cheat engine memory region print screen
 Filesize:  50.54 KB
 Viewed:  2807 Time(s)

ce_mame.png



vmmap_mame.png
 Description:
sysinternals' vmmap
 Filesize:  110.96 KB
 Viewed:  2807 Time(s)

vmmap_mame.png


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