Windows 7 Architectural and Internal Security Improvements - Required Driver Signing

Drivers typically run as part of the kernel, which gives them almost unprotected access to system resources. As a result, drivers that have bugs or are poorly written, or malware drivers specifically written to abuse these privileges, can significantly affect a computer’s reliability and security.

To help reduce the impact of drivers, Microsoft introduced driver signing beginning with Microsoft Windows 2000. Signed drivers have a digital signature that indicates they have been approved by Microsoft and are likely to be free from major weaknesses that might affect system reliability. Administrators can configure Windows 2000 and later operating systems to block all unsigned drivers, which can dramatically decrease the risk of driver-related problems.

However, the large number of unsigned 32-bit drivers has made blocking unsigned drivers impractical for most organizations. As a result, most existing Windows computers allow unsigned drivers to be installed.

With 64-bit versions of Windows Vista and Windows 7, all kernel-mode drivers must be digitally signed. A kernel module that is corrupt or has been subject to tampering will not load. Any driver that is not properly signed cannot enter the kernel space and will fail to load. Although a signed driver is not a guarantee of security, it does help identify and prevent many malicious attacks while allowing Microsoft to help developers improve the overall quality of drivers and reduce the number of driver-related crashes.

Mandatory driver signing also helps improve the reliability of Windows Vista and Windows 7 because many system crashes result from vulnerabilities in kernel-mode drivers. Requiring the authors of these drivers to identify themselves makes it easier for Microsoft to determine the cause of system crashes and work with the responsible vendor to resolve the issue. System administrators also benefit from digitally signed and identified drivers because they get additional visibility into software inventory and install state on client computers. From a compatibility perspective, existing Windows Hardware Quality Labs–certified x64 kernel drivers are considered validly signed in Windows Vista and Windows 7.

Source of Information : Windows 7 Resource Kit 2009 Microsoft Press

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