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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz
Hello everyone, I'm failing when trying to allocate memory twice at different address. For example:
Code:
myaddr = 0x400000
myaddr2 = 0x401000
mysize = 0x200
...
invoke VirtualAlloc,myaddr,mysize,MEM_COMMIT+MEM_RESERVE,PAGE_EXECUTE_READWRITE ;first time -> OK.
invoke VirtualAlloc,myaddr2,mysize,MEM_COMMIT+MEM_RESERVE,PAGE_EXECUTE_READWRITE ;failed, ERROR_INVALID_ADDRESS    

Why Question Sad
P.S playing with PE format.
Post 04 Jan 2012, 18:21
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
let the system do it for you the second call.
Post 04 Jan 2012, 19:49
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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz
typedef
What you mean ?
Post 04 Jan 2012, 20:03
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
Leave out the address parameter to null and the system will find the appropriate address for you
Post 04 Jan 2012, 20:09
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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz
I know that, but I need it to be allocated at that address :/ trying to write windows PE loader manually.
I did like this, but imports are not correct Sad I don't know what is happening..
Image is loaded at 50000000h, file is in buffer and when I allocated space equal to IMAGE_NT_HEADERS.OptionalHeader.SizeOfImage and copied IMAGE_DOS_HEADER, IMAGE_NT_HEADERS and all sections there, but it didn't loaded cause of import calls are wrong. Did I miss something ?
Post 04 Jan 2012, 20:31
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aq83326



Joined: 25 Jun 2011
Posts: 21
aq83326
http://blogs.msdn.com/b/oldnewthing/archive/2003/10/08/55239.aspx

Maybe:
VirtualAlloc cannot reserve a reserved page, but the documentation doesn't say what happens if you try to do so-I'd like to know what happens too.

The allocation granularity is likely 64k, thus the first call to VirtualAlloc reserves and commits 64k rather than the single page necessary to hold 200h.

So even though the addresses are likely a page apart (4k being the usual page size) you are reserving a reserved page.

So see what happens when you try to reserve a reserved page and try just using MEM_COMMIT by itself for that second line to see what happens.
Post 05 Jan 2012, 07:06
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Overflowz



Joined: 03 Sep 2010
Posts: 1046
Overflowz
Thanks, I'm working on it now.
Post 05 Jan 2012, 08:55
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f0dder



Joined: 19 Feb 2004
Posts: 3170
Location: Denmark
f0dder
Check http://msdn.microsoft.com/en-us/library/windows/desktop/ms724958%28v=vs.85%29.aspx , notably the allocation granularity - don't blindly assume 64k.
Post 05 Jan 2012, 23:27
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