Strong Stack Protector
Requires the kernel to be built with CONFIG_STACKPROTECTOR_STRONG=y, extending canary coverage to many more functions.
Checked against the resolved running state (e.g. sshd -T, sysctl, systemctl show), catches drop-ins and Includes a file read would miss. Caveat: runtime ≠ persistence; a value correct now may not survive a reboot.
Pavois asserts the effective configuration, the live, resolved state, not a file. File-based scanners (OVAL/SCAP, Lynis) miss Includes, drop-ins and runtime defaults; this check sees what is actually applied.
A mapping is a cross-reference to where each standard places this requirement, anchored and cross-validated, not a claim of equivalence. A passing check is evidence toward these references, how to read it.
Why this rule matters
CONFIG_STACKPROTECTOR_STRONG=y extends the basic stack-protector by emitting a canary for a much broader set of functions, any function with local array variables, references to local frame addresses, or certain register-spilling patterns, not just those with large char buffers. This closes the gap where the basic protector left many overflow-prone functions unguarded, while keeping a sensible balance between coverage and performance.
What Pavois checks
Pavois reads the build configuration of the running kernel via /boot/config-$(uname -r) or /proc/config.gz and confirms CONFIG_STACKPROTECTOR_STRONG=y. Reading the effective config of the booted kernel proves the stronger canary coverage is compiled into the kernel actually in use.
describe command("C=/boot/config-$(uname -r); if [ -r \"$C\" ]; then cat \"$C\"; elif zcat /proc/config.gz 2>/dev/null | head -1 | grep -q .; then zcat /proc/config.gz; else echo PAVOIS_NO_KERNEL_CONFIG; fi | grep -E '^(CONFIG_STACKPROTECTOR_STRONG=|PAVOIS_NO_KERNEL_CONFIG)'") do
its('stdout') { should_not match(/PAVOIS_NO_KERNEL_CONFIG/) }
its('stdout') { should match(/^CONFIG_STACKPROTECTOR_STRONG=y$/) }
endHow to verify it is applied
grep '^CONFIG_STACKPROTECTOR_STRONG=' /boot/config-$(uname -r) || zcat /proc/config.gz | grep '^CONFIG_STACKPROTECTOR_STRONG='
Expected output: CONFIG_STACKPROTECTOR_STRONG=y.
Inspect & investigate
Like the basic protector, a detected canary corruption produces a fatal kernel message, look in dmesg or journalctl -k for stack-protector: Kernel stack is corrupted in: .... Otherwise there is no routine log output; confirm the option with the grep command above.
Remediation
No automated remediation is shipped: CONFIG_STACKPROTECTOR_STRONG is a compile-time kernel option and cannot be enabled at runtime. The fix is to boot a kernel built with it enabled, the stock distribution kernels for the supported OSes already do. For a custom kernel, set CONFIG_STACKPROTECTOR_STRONG=y and rebuild.
Pavois applies this with its own harden engine, the plan below, not a shell script:
| resource | kernel_build |
|---|
pavois harden plan localwhere the target is local, a user@host SSH alias, or a container , Docs
Impact & precautions
With only the basic protector (or none), many overflow-prone kernel functions ship without a canary, leaving stack-smashing paths exploitable. Precautions: remediation means a kernel change and a reboot, schedule a maintenance window and keep the prior kernel in GRUB as a fallback. The added coverage costs a small, well-characterized overhead (typically low single-digit percent) that is acceptable for virtually all systems.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R15 | direct | 2.0 | high |
Each reference is a cross-reference anchored in the upstream benchmark and cross-validated against the SCAP Security Guide and ansible-lockdown, not a claim of equivalence. Direct = a prescriptive, line-level requirement; supporting = an abstract control family (NIST) the check provides evidence toward. How to read a mapping.