#Win32k sys blue screen windows 7 driver#
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#Win32k sys blue screen windows 7 software#

It should be noted, however, that not allВ non-guarded accesses to user-mode memory are dangerous by definition: regions previously secured by the MmSecureVirtualMemoryВ API andВ special areas such as TEB or PEB are not affected. If there are no exception records present, or all of them have their TryLevel fields set to 0xFFFFFFFE, then an exception occurring right at that moment could potentially bring the operating system down. Therefore, the Bochs instrumentation can iterate through the SEH chain, determine which handlers are enabled and which functions they correspond to.

PAGE:00671D02 mov, 0FFFFFFFEhД¬onsequently, the overall callstack at the time of any user-mode memory access may look similarly to the following: Below is an example of a try/except block encapsulating the writing a single DWORD value into user-mode memory: PAGE:00671CF3 mov, 1 ThereвЂ™s also an example on the Handling Exceptions MSDN page: try blocks are denoted by writing their 0-based indexes into the TryLevel fields, and later overwriting them with -2 (0xFFFFFFFE) when the blocks are closed and exception handling is disabled.

#Win32k sys blue screen windows 7 driver#

Note that subsequent accesses by the driver to the user-mode buffer must also be encapsulated within a try/except block: a malicious application could have another thread deleting, substituting, or changing the protection of user address ranges at any time (even after or during a call to ProbeForRead or ProbeForWrite). If the routine raises an exception, the driver should complete the IRP with the appropriate error. As the documentation of the Windows ProbeForRead function states:Дrivers must call ProbeForRead inside a try/except block. One intuitive example of such pattern is the lack of exception handling being set up at the time of accessing ring-3 memory area. Specifically, one of my goals was to develop more patterns (based on memory accesses or other events) which could signal problems in kernel-mode code other than just double fetches.

#Win32k sys blue screen windows 7 full#

We believe it also played a significant role in popularizing the double-fetch vulnerability class and the concept ofВ using system-wide instrumentation for security, as several other fruitful projects ensued as a result, probably most notable of which is Xenpwn.ДЄfter all this time, I decided to get back onВ the subject of full system instrumentation and analyzing various execution traces in search of indicators ofВ potential vulnerabilities. The project was called Bochspwn (or kfetch-toolkit on Github) and was largely successful, leading to the discovery of several dozen serious vulnerabilities in the Windows kernel. The purpose of the emulation (and our custom embedded instrumentation) was to capture detailed information about accesses to user-mode memory originating from the kernel, so that we could later run analysis tools to discover multiple references to single memory addresses within the scope of one system call, and produce meaningful reports.

#Win32k sys blue screen windows 7 software#

Back in 2013, Gynvael and I published the results of our research into discovering so-called double fetch vulnerabilities in operating system kernels, by running them in full software emulation mode inside of an IA-32В emulator called Bochs.