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Re: win32/memory locking (Re: Reply to EFS note on Bugtraq)
From: John Wiltshire <jw () QITS NET AU>
Date: Wed, 24 Jan 2001 14:07:19 +1000

From: Peter W [mailto:peterw () USA NET]

Bits _never_ get written to the disk? Guaranteed never to use 
swap space?

The GnuPG FAQ (http://www.gnupg.org/faq.html#q6.1) suggests that it is
not possible to make a Windows program insist on physical RAM 
the way a
program can in Open Systems. Does EFS really use only physical RAM? If
so, is there some win32 API that can be used by other 
application designers
who want to guarantee that certain blocks of allocated memory 
are *never*
swapped out to disk? The most likely candidate I've come across is
VirtualLock() which, unfortunately, "does not mean that the 
page will not be
paged to disk" 
(http://msdn.microsoft.com/library/techart/msdn_virtmm.htm).


This is certainly possible as EFS is a kernel mode device driver and not
a Win32 application.  Non pageable memory can be easily allocated from
the non-paged pool by a device driver (and is one of the fundamental
concepts in writing a Win2000 driver).  

The EFS driver communicates with the local security authority (lsass) to
allow the use of CryptoAPI for encryption of the data, but as lsass is a
Native applciation (not Win32) then it may have access to other
(undocumented) functions, or simply pass a pointer to the non-paged
memory it has allocated for the encryption buffers.

Note that the PGP implementation uses a device driver (PGPmemlock.sys)
to lock pages into memory and prevent them from being swapped out.  I am
unsure as to the motives of the GPG team if they have not implemented a
similar feature, but smells like FUD to me.

John Wiltshire


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  • Re: win32/memory locking (Re: Reply to EFS note on Bugtraq) John Wiltshire (Jan 24)
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