linux-kernel - [PATCH] docs: make kptr_restrict and hash

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Message-Id: <20251205-doc-hash-ptr-v1-1-573966cfa404@linux.intel.com>
Date: Fri, 05 Dec 2025 01:00:53 +0000
From: Marc Herbert <marc.herbert@...ux.intel.com>
To: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Rick Edgecombe <rick.p.edgecombe@...el.com>, 
 Marc Herbert <marc.herbert@...ux.intel.com>
Subject: [PATCH] docs: make kptr_restrict and hash_pointers reference each
 other

vsprintf.c uses a mix of the `kernel.kptr_restrict` sysctl and the
`hash_pointers` boot param to control pointer hashing. But that wasn't
possible to tell without looking at the source code.

They have a different focus and purpose. To avoid wasting the time of
users trying to use one instead of the other, simply have them reference
each other in the Documentation.

Signed-off-by: Marc Herbert <marc.herbert@...ux.intel.com>
---
(please just go ahead with any minor corrections; I mean do not ask
for my opinion)
---
 Documentation/admin-guide/kernel-parameters.txt | 3 +++
 Documentation/admin-guide/sysctl/kernel.rst     | 2 ++
 2 files changed, 5 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6c42061ca20e..b4305fa17a19 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1867,6 +1867,9 @@
 				 param "no_hash_pointers" is an alias for
 				 this mode.
 
+			For controlling hashing dynamically at runtime,
+			use the sysctl `kernel.kptr_restrict` instead.
+
 	hashdist=	[KNL,NUMA] Large hashes allocated during boot
 			are distributed across NUMA nodes.  Defaults on
 			for 64-bit NUMA, off otherwise.
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index f3ee807b5d8b..8833e1364ab9 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -576,6 +576,8 @@ if leaking kernel pointer values to unprivileged users is a concern.
 When ``kptr_restrict`` is set to 2, kernel pointers printed using
 %pK will be replaced with 0s regardless of privileges.
 
+For disabling these security restrictions early at boot time (and once
+for all), use the ``hash_pointers`` boot parameter instead.
 
 modprobe
 ========

---
base-commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449
change-id: 20251204-doc-hash-ptr-00e46e1a5398

Best regards,
--  
Marc Herbert <marc.herbert@...ux.intel.com>