Information
Syscalls are special routines in the Linux kernel, which userspace applications ask to do privileged tasks. Invoking a system call is an expensive operation because the processor must interrupt the currently executing task and switch context to kernel mode and then back to userspace after the system call completes. Virtual Syscalls map into user space a page that contains some variables and the implementation of some system calls. This allows the system calls to be executed in userspace to alleviate the context switching expense.
Virtual Syscalls provide an opportunity of attack for a user who has control of the return instruction pointer. Disabling vsyscalls help to prevent return oriented programming (ROP) attacks via buffer overflows and overruns.
Satisfies: SRG-OS-000134-GPOS-00068, SRG-OS-000433-GPOS-00192
Solution
Configure RHEL 8 to disable vsyscalls with the following commands:
$ sudo grubby --update-kernel=ALL --args='vsyscall=none'
Add or modify the following line in '/etc/default/grub' to ensure the configuration survives kernel updates:
GRUB_CMDLINE_LINUX='vsyscall=none'