Another classic and powerful method of infecting the kernel is by infecting the kernel's VFS layer. This technique is wonderful and quite stealthy since it technically modifies the data segment in the memory and not the text segment, where discrepancies are easier to detect. The VFS layer is very object-oriented and contains a variety of structs with function pointers. These function pointers are filesystem operations such as open, read, write, readdir, and so on. If an attacker can patch these function pointers, then they can take control of these operations in any way that they see fit.
There are probably several techniques out there for detecting this type of infection. The general idea, however, is to validate the function pointer addresses and confirm that they are pointing to the expected functions. In most cases, these should be pointing to functions within the kernel and not to functions that exist in LKMs. One quick approach to detecting...