linux-kernel - [PATCH] admin-guide/hw-vuln/core-scheduling: fix return type of PR_SCHED_CORE

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Message-Id: <20240423-core-scheduling-cookie-v1-1-5753a35f8dfc@weissschuh.net>
Date: Tue, 23 Apr 2024 12:34:25 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, 
 Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>, 
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
 Jonathan Corbet <corbet@....net>, 
 "Joel Fernandes (Google)" <joel@...lfernandes.org>, 
 Chris Hyser <chris.hyser@...cle.com>, Josh Don <joshdon@...gle.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] admin-guide/hw-vuln/core-scheduling: fix return type of
 PR_SCHED_CORE_GET

sched_core_share_pid() copies the cookie to userspace with
put_user(id, (u64 __user *)uaddr), expecting 64 bits of space.
The "unsigned long" datatype that is documented in core-scheduling.rst
however is only 32 bits large on 32 bit architectures.

Document "unsigned long long" as the correct data type that is always
64bits large.

This matches what the selftest cs_prctl_test.c has been doing all along.

Fixes: 0159bb020ca9 ("Documentation: Add usecases, design and interface for core scheduling")
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/util-linux/df7a25a0-7923-4f8b-a527-5e6f0064074d@t-8ch.de/
Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 Documentation/admin-guide/hw-vuln/core-scheduling.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/core-scheduling.rst b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
index cf1eeefdfc32..a92e10ec402e 100644
--- a/Documentation/admin-guide/hw-vuln/core-scheduling.rst
+++ b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
@@ -67,8 +67,8 @@ arg4:
     will be performed for all tasks in the task group of ``pid``.
 
 arg5:
-    userspace pointer to an unsigned long for storing the cookie returned by
-    ``PR_SCHED_CORE_GET`` command. Should be 0 for all other commands.
+    userspace pointer to an unsigned long long for storing the cookie returned
+    by ``PR_SCHED_CORE_GET`` command. Should be 0 for all other commands.
 
 In order for a process to push a cookie to, or pull a cookie from a process, it
 is required to have the ptrace access mode: `PTRACE_MODE_READ_REALCREDS` to the

---
base-commit: 71b1543c83d65af8215d7558d70fc2ecbee77dcf
change-id: 20240423-core-scheduling-cookie-b0551c40b086

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>