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Date: Sun, 10 Apr 2022 21:34:17 +0200
From: Peter Gerber <peter@...tirary.ch>
To: kernel-hardening@...ts.openwall.com
Cc: linux-hardening@...r.kernel.org
Subject: Kernel Self Protection Project: slub_debug=ZF
Hello,
The Kernel Self Protection Project, on their Recommended Settings [1]
page, suggests the following:
# Enable SLUB redzoning and sanity checking (slow; requires
CONFIG_SLUB_DEBUG=y above).
slub_debug=ZF
On recent kernels, I see the following in dmesg when this option is set:
**********************************************************
** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
** **
** This system shows unhashed kernel memory addresses **
** via the console, logs, and other interfaces. This **
** might reduce the security of your system. **
** **
** If you see this message and you are not debugging **
** the kernel, report this immediately to your system **
** administrator! **
** **
** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
**********************************************************
A bit of digging tells me that this is caused by "slub: force on
no_hash_pointers when slub_debug is enabled" [2]. Assuming the
performance impact is acceptable, is this option still recommend? Should
there perhaps be a way to explicitly disable no_hash_pointers (e.g. via
no_hash_pointers=off)?
Regards,
Peter
[1]:
https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings
[2]:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=792702911f581f7793962fbeb99d5c3a1b28f4c3
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