Vulnerability Discussion

System calls 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 system calls 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 system calls provide an opportunity of attack for a user who has control of the return instruction pointer. Disabling virtual system calls help to prevent return-oriented programming attacks via buffer overflows and overruns.

Check

Verify RHEL 10 is configured so that the current GRUB 2 configuration disables virtual system calls with the following command:

$ sudo grubby --info=ALL | grep args | grep -v 'vsyscall=none'

If any output is returned, this is a finding.

Check that virtual system calls are disabled by default to persist in kernel updates with the following command:

$ sudo grep vsyscall /etc/default/grub
GRUB_CMDLINE_LINUX="vsyscall=none"

If "vsyscall" is not set to "none", is missing or commented out, and is not documented with the information system security officer as an operational requirement, this is a finding.

Fix

Configure RHEL 10 to disable virtual system calls with the following command:

$ sudo grubby --update-kernel=ALL --args="vsyscall=none"