Limit sampling frequency of the Perf system

An XCCDF Rule

Description

To set the runtime status of the kernel.perf_event_max_sample_rate kernel parameter, run the following command:

$ sudo sysctl -w kernel.perf_event_max_sample_rate=1

To make sure that the setting is persistent, add the following line to a file in the directory /etc/sysctl.d:

kernel.perf_event_max_sample_rate = 1

Rationale

The kernel.perf_event_max_sample_rate parameter configures maximum frequency of collecting of samples for the Perf system. It is expressed in samples per second. Restricting usage of Perf system decreases risk of potential availability problems.

ID: xccdf_org.ssgproject.content_rule_sysctl_kernel_perf_event_max_sample_rate
Severity: Medium
References: CCE-91259-2

R9
Updated: 5 days ago

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - CCE-91259-2
  - disable_strategy  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_perf_event_max_sample_rate

- name: List /etc/sysctl.d/*.conf files
  find:
    paths:
    - /run/sysctl.d/
    - /etc/sysctl.d/
    - /usr/local/lib/sysctl.d/
    - /lib/sysctl.d/
    contains: ^[\s]*kernel.perf_event_max_sample_rate.*$
    patterns: '*.conf'
    file_type: any
  register: find_sysctl_d
  when: '"kernel-default" in ansible_facts.packages'
  tags:
  - CCE-91259-2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_perf_event_max_sample_rate

- name: Comment out any occurrences of kernel.perf_event_max_sample_rate from config
    files
  replace:
    path: '{{ item.path }}'
    regexp: ^[\s]*kernel.perf_event_max_sample_rate
    replace: '#kernel.perf_event_max_sample_rate'
  loop: '{{ find_sysctl_d.files }}'
  when: '"kernel-default" in ansible_facts.packages'
  tags:
  - CCE-91259-2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_perf_event_max_sample_rate

- name: Comment out any occurrences of kernel.perf_event_max_sample_rate from /etc/sysctl.conf
  replace:
    path: /etc/sysctl.conf
    regexp: ^[\s]*kernel.perf_event_max_sample_rate
    replace: '#kernel.perf_event_max_sample_rate'
  when: '"kernel-default" in ansible_facts.packages'
  tags:
  - CCE-91259-2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_perf_event_max_sample_rate

- name: Ensure sysctl kernel.perf_event_max_sample_rate is set to 1
  sysctl:
    name: kernel.perf_event_max_sample_rate
    value: '1'
    sysctl_file: /etc/sysctl.d/kernel_perf_event_max_sample_rate.conf
    state: present
    reload: true
  when: '"kernel-default" in ansible_facts.packages'
  tags:
  - CCE-91259-2
  - disable_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - reboot_required
  - sysctl_kernel_perf_event_max_sample_rate

# Remediation is applicable only in certain platforms
if rpm --quiet -q kernel-default; then

# Comment out any occurrences of kernel.perf_event_max_sample_rate from /etc/sysctl.d/*.conf files

for f in /etc/sysctl.d/*.conf /run/sysctl.d/*.conf /usr/local/lib/sysctl.d/*.conf /lib/sysctl.d/*.conf; do

  # skip systemd-sysctl symlink (/etc/sysctl.d/99-sysctl.conf -> /etc/sysctl.conf)
  if [[ "$(readlink -f "$f")" == "/etc/sysctl.conf" ]]; then continue; fi

  matching_list=$(grep -P '^(?!#).*[\s]*kernel.perf_event_max_sample_rate.*$' $f | uniq )
  if ! test -z "$matching_list"; then
    while IFS= read -r entry; do
      escaped_entry=$(sed -e 's|/|\\/|g' <<< "$entry")
      # comment out "kernel.perf_event_max_sample_rate" matches to preserve user data
      sed -i --follow-symlinks "s/^${escaped_entry}$/# &/g" $f
    done <<< "$matching_list"
  fi
done

#
# Set sysctl config file which to save the desired value
#

SYSCONFIG_FILE='/etc/sysctl.d/kernel_perf_event_max_sample_rate.conf'


#
# Set runtime for kernel.perf_event_max_sample_rate
#
/sbin/sysctl -q -n -w kernel.perf_event_max_sample_rate="1"

#
# If kernel.perf_event_max_sample_rate present in /etc/sysctl.conf, change value to "1"
#	else, add "kernel.perf_event_max_sample_rate = 1" to /etc/sysctl.conf
#

sed -i "/^$SYSCONFIG_VAR/d" /etc/sysctl.conf

# Strip any search characters in the key arg so that the key can be replaced without
# adding any search characters to the config file.
stripped_key=$(sed 's/[\^=\$,;+]*//g' <<< "^kernel.perf_event_max_sample_rate")

# shellcheck disable=SC2059
printf -v formatted_output "%s = %s" "$stripped_key" "1"

# If the key exists, change it. Otherwise, add it to the config_file.
# We search for the key string followed by a word boundary (matched by \>),
# so if we search for 'setting', 'setting2' won't match.
if LC_ALL=C grep -q -m 1 -i -e "^kernel.perf_event_max_sample_rate\\>" "${SYSCONFIG_FILE}"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^kernel.perf_event_max_sample_rate\\>.*/$escaped_formatted_output/gi" "${SYSCONFIG_FILE}"
else
    if [[ -s "${SYSCONFIG_FILE}" ]] && [[ -n "$(tail -c 1 -- "${SYSCONFIG_FILE}" || true)" ]]; then
        LC_ALL=C sed -i --follow-symlinks '$a'\\ "${SYSCONFIG_FILE}"
    fi
    cce="CCE-91259-2"
    printf '# Per %s: Set %s in %s\n' "${cce}" "${formatted_output}" "${SYSCONFIG_FILE}" >> "${SYSCONFIG_FILE}"
    printf '%s\n' "$formatted_output" >> "${SYSCONFIG_FILE}"
fi

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

Limit sampling frequency of the Perf system

Description

Rationale

Remediation - Ansible

Remediation - Shell Script