Control-flow integrity in 5.13

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2021-05-27 04:30:02

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By Jonathan Corbet May 21, 2021 Among the many changes merged for the 5.13 kernel is support for the LLVM control-flow integrity (CFI) mechanism. CFI defends against exploits by ensuring that indirect function calls have not been redirected by an attacker. Quite a bit of work was needed to make this feature work well for the kernel, but the result appears to be production-ready and able to defend Linux systems from a range of attacks.

The kernel depends heavily on indirect function calls — calls where the destination address is not known at compile time. Device drivers, filesystems, and other kernel subsystems interface with the generic, core code by providing functions to be called to carry out specific actions. When the time comes to, for example, open a file (which may be a special file corresponding to a device), the core kernel will make an indirect call to the appropriate open() function defined in the file_operations structure for the file in question. Indirect function calls allow for a clean separation between generic and low-level code.