Disable the 32-bit vDSO
Ensures the running kernel is built without CONFIG_COMPAT_VDSO, so the vDSO is randomized instead of mapped at a fixed legacy address.
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_COMPAT_VDSO=y maps the vDSO at a fixed, predictable address for compatibility with very old glibc versions. A fixed vDSO mapping defeats its randomization and gives attackers a reliable, known location of executable code in every process, a ready source of gadgets for ROP-style exploitation. It also hurts performance. Leaving it unset keeps the vDSO randomized (full ASLR) and removes that predictable code region.
What Pavois checks
Pavois reads the build-time config of the running kernel via /boot/config-$(uname -r) (fallback /proc/config.gz) and asserts the line is not CONFIG_COMPAT_VDSO=y. Keying on uname -r matches the exact booted image, more reliable than reading a random /boot/config-*.
describe command("C=/boot/config-$(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_COMPAT_VDSO=|PAVOIS_NO_KERNEL_CONFIG)'") do
its('stdout') { should_not match(/PAVOIS_NO_KERNEL_CONFIG/) }
its('stdout') { should_not match(/^CONFIG_COMPAT_VDSO=y$/) }
endHow to verify it is applied
Run grep -h '^CONFIG_COMPAT_VDSO=' /boot/config-$(uname -r) (or zcat /proc/config.gz | grep COMPAT_VDSO). Expected: # CONFIG_COMPAT_VDSO is not set or no output. You can see the vDSO mapping per process in cat /proc/self/maps (look for [vdso]); its address should vary between runs when randomized.
Inspect & investigate
Static kernel build option, no runtime log. Inspect with zcat /proc/config.gz | grep COMPAT_VDSO or grep COMPAT_VDSO /boot/config-$(uname -r). Observe the live vDSO placement with grep vdso /proc/self/maps across several runs.
Remediation
No automated remediation is shipped: this is a kernel compile-time option. Apply it by booting a kernel built without CONFIG_COMPAT_VDSO (the modern default), or rebuild the kernel. pavois harden apply cannot change it.
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
Risk if enabled: the vDSO sits at a fixed address in every process, providing attackers a predictable code region for ROP and weakening ASLR.
Precautions before changing it: the compat vDSO only matters for glibc older than ~2.3.3 (early 2000s); no modern userland depends on it, so disabling has effectively no functional impact. Changing kernels requires a reboot; keep the previous kernel in GRUB as a fallback and validate boot on a console.
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.