Force initialization of variables containing userspace addresses
Requires the kernel to be built with CONFIG_GCC_PLUGIN_STRUCTLEAK=y, a GCC plugin that forces zero-initialization of local structures that may carry userspace data.
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
Initializing structures from userspace can prevent some classes of information exposure.
What Pavois checks
Pavois reads the effective build flag of the running kernel via /boot/config-$(uname -r) or /proc/config.gz, keyed on $(uname -r), so it reflects the booted image rather than a stray .config a fixed-path file scan might match.
describe command("grep -hE '^(CONFIG_GCC_PLUGIN_STRUCTLEAK|CONFIG_INIT_STACK_ALL_ZERO)=y' /boot/config-$(uname -r) 2>/dev/null; zcat /proc/config.gz 2>/dev/null | grep -E '^(CONFIG_GCC_PLUGIN_STRUCTLEAK|CONFIG_INIT_STACK_ALL_ZERO)=y'") do
its('stdout') { should match(/=y$/) }
endHow to verify it is applied
Run grep '^CONFIG_GCC_PLUGIN_STRUCTLEAK=' /boot/config-$(uname -r) (or zcat /proc/config.gz | grep '^CONFIG_GCC_PLUGIN_STRUCTLEAK='). Expected output: CONFIG_GCC_PLUGIN_STRUCTLEAK=y. Absent or # ... is not set is a failure.
Inspect & investigate
This plugin is a compile-time transformation with no dedicated runtime log; its effect is the absence of info leaks. Confirm the flag with zcat /proc/config.gz | grep STRUCTLEAK.
Remediation
No automated remediation is shipped: a kernel build option cannot be set by editing a file. Apply it manually by installing and booting a kernel compiled with CONFIG_GCC_PLUGIN_STRUCTLEAK=y.
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
When the kernel copies a structure back to userspace, any field or padding byte left uninitialized carries whatever was previously on the stack, leftover kernel pointers or secrets, producing an information leak that helps defeat KASLR and stage further attacks. The structleak plugin forces zero-initialization of local structures that can reach userspace, so no stale stack content escapes. The basic mode targets structures with userspace-bound data; the stricter BYREF_ALL variant covers more. Without it, a class of uninitialized-structure info leaks remains exploitable. This is a build-time option needing GCC plugin support, set only by booting a kernel compiled with it. Precautions: there is a modest runtime cost from the extra zeroing; switching to a hardened kernel changes module ABI, so validate driver loading off production before deploying. No reboot risk beyond a normal kernel swap.
Standards mapping
| Standard | Reference | Type | Version | Confidence |
|---|---|---|---|---|
| ANSSI BP-028 | R21 | 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.