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Merged
adrelanos merged 1 commit into from
Oct 10, 2025
Merged

Docs detailing future improvements to slab_debug #325

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1 change: 1 addition & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@ Kernel space:

- Enable sanity checks and red zoning via slab debugging. This will implicitly
disable kernel pointer hashing, leaking very sensitive information to root.
Re-enabling hashed pointers will be possible when using Linux kernel >= 6.17.

- Enable memory zeroing at both allocation and free time, which mitigates some
use-after-free vulnerabilities by erasing sensitive information in memory.
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10 changes: 7 additions & 3 deletions etc/default/grub.d/40_kernel_hardening.cfg#security-misc-shared
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Expand Up @@ -39,18 +39,22 @@ kver="$(dpkg-query --show --showformat='${Version}' "$kpkg")" 2>/dev/null || tru
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX slab_nomerge"

## Enable sanity checks and red zoning of slabs via debugging options to detect corruption.
## As a by product of debugging, this will implicitly disabling kernel pointer hashing.
## Enabling will therefore leak exact and all kernel memory addresses to root.
## As a by product of debugging, this will implicitly disabling kernel pointer hashing unless manually re-enabled.
## Enabling this (for now) will therefore leak exact and all kernel memory addresses to root.
## Has the potential to cause a noticeable performance decrease.
##
## https://www.kernel.org/doc/html/latest/mm/slub.html
## https://lore.kernel.org/all/20210601182202.3011020-5-swboyd@chromium.org/T/#u
## https://gitlab.tails.boum.org/tails/tails/-/issues/19613
## https://github.com/Kicksecure/security-misc/issues/253
##
## KSPP=yes
## KSPP=partial
## KSPP sets the kernel parameters and CONFIG_SLUB_DEBUG.
##
## TODO: Debian 14
## The first parameter is applicable when using Linux kernel >= 6.17 (retained here for future-proofing and completeness).
##
#GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX hash_pointers=always"
GRUB_CMDLINE_LINUX="$GRUB_CMDLINE_LINUX slab_debug=FZ"

## Zero memory at allocation time and free time.
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