SV-257792r1184289: RHEL 9 must disable virtual system calls. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 9 must disable virtual system calls.

Description

Discussion Text

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 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 user space 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. Satisfies: SRG-OS-000480-GPOS-00227, SRG-OS-000134-GPOS-00068

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-001084

References

DPMS Target Red Hat Enterprise Linux 9 DISA DPMS Target Red Hat Enterprise Linux 9 5551

Checks

DISA STIG (Manual Reference)

Verify 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 (ISSO) as an operational requirement, this is a finding.

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

#!/bin/bash
# Reconstructed from oval:mil.disa.stig.rhel9os:def:257792
# RHEL 9 must disable virtual system calls.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (grep -rhP --include='*.conf' '^options\s+(.*)$' '/boot/loader/entries' | sed -En 's/^options\s+(.*)$/\1/p') | grep -Pq '(^|\s)vsyscall=none(\s|$)'
}
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^GRUB_CMDLINE_LINUX="(.*)"/\1/p' '/etc/default/grub') | grep -Pq '(^|\s)vsyscall=none(\s|$)'
}

if ( test_1 && test_2 ); then
  echo "PASS"
else
  echo "FAIL"
fi

Assessment Script Powered by AISandbox-executed

A standalone Shell script to assess this control automatically. Review before running it in your environment.

Syntax-checked and actually executed in an isolated sandbox (not the real system this checks) — confirmed to run without errors.

#!/bin/sh
# DISA STIG RHEL 9 must disable virtual system calls (oval:mil.disa.stig.rhel9os:def:257792)

if grep -q '(^|\s)vsyscall=none(\s|$)' /boot/loader/entries/*conf; then
    if grep -q '(^|\s)vsyscall=none(\s|$)' /etc/default/grub; then
        echo "PASS"
        exit 0
    fi
fi
echo "FAIL"
exit 1

Remediation

Document the use of virtual system calls with the ISSO as an operational requirement or disable them with the following command:

$ 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"