Exploit Methods/Function pointer overwrite

Details

When an attacker has a write primitive, they can overwrite function pointers to redirect execution. Function pointers exist in a large number of places in the kernel ranging from function pointer tables (e.g. fops), to vector and descriptor tables.

Examples

• security_operations overwrite
• IDT, timer_list_fops, or security_operations overwrite

Mitigations

• mark function pointer tables "const" when they can be statically assigned, making them read-only for the entire kernel runtime.
• use __ro_after_init on function pointer tables that are only written during __init so they are read-only during the rest of the kernel runtime.
• make all function pointer tables read-only at compile time (e.g. PAX_CONSTIFY_PLUGIN).
• make sensitive targets that need only occasional updates only writable during rare updates (e.g. PAX_KERNEXEC).