Subject: [patch V5 09/12] [RFC] coccinelle: misc: Add scoped_masked_$MODE_access() checker script

From: Thomas Gleixner <[email-masked]>
Date: Mon, 27 Oct 2025 09:43:58 +0100 (CET)

A common mistake in user access code is that the wrong access mode is
selected for starting the user access section. As most architectures map
Read and Write modes to ReadWrite this goes often unnoticed for quite some
time.

Aside of that the scoped user access mechanism requires that the same
pointer is used for the actual accessor macros that was handed in to start
the scope because the pointer can be modified by the scope begin mechanism
if the architecture supports masking.

Add a basic (and incomplete) coccinelle script to check for the common
issues. The error output is:

kernel/futex/futex.h:303:2-17: ERROR: Invalid pointer for unsafe_put_user(p) in scoped_masked_user_write_access(to)
kernel/futex/futex.h:292:2-17: ERROR: Invalid access mode unsafe_get_user() in scoped_masked_user_write_access()

Not-Yet-Signed-off-by: Thomas Gleixner <[email-masked]>
Cc: Julia Lawall <[email-masked]>
Cc: Nicolas Palix <[email-masked]>
---
 scripts/coccinelle/misc/scoped_uaccess.cocci |  108 +++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)

--- /dev/null
+++ b/scripts/coccinelle/misc/scoped_uaccess.cocci
@@ -0,0 +1,108 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Validate scoped_masked_user*access() scopes
+///
+// Confidence: Zero
+// Options: --no-includes --include-headers
+
+virtual context
+virtual report
+virtual org
+
+@initialize:python@
+@@
+
+scopemap = {
+  'scoped_user_read_access_size'  : 'scoped_user_read_access',
+  'scoped_user_write_access_size' : 'scoped_user_write_access',
+  'scoped_user_rw_access_size'    : 'scoped_user_rw_access',
+}
+
+# Most common accessors. Incomplete list
+noaccessmap = {
+  'scoped_user_read_access'       : ('unsafe_put_user', 'unsafe_copy_to_user'),
+  'scoped_user_write_access'      : ('unsafe_get_user', 'unsafe_copy_from_user'),
+}
+
+# Most common accessors. Incomplete list
+ptrmap = {
+  'unsafe_put_user'			 : 1,
+  'unsafe_get_user'			 : 1,
+  'unsafe_copy_to_user'		 	 : 0,
+  'unsafe_copy_from_user'		 : 0,
+}
+
+print_mode = None
+
+def pr_err(pos, msg):
+   if print_mode == 'R':
+      coccilib.report.print_report(pos[0], msg)
+   elif print_mode == 'O':
+      cocci.print_main(msg, pos)
+
+@r0 depends on report || org@
+iterator name scoped_user_read_access,
+	      scoped_user_read_access_size,
+	      scoped_user_write_access,
+	      scoped_user_write_access_size,
+	      scoped_user_rw_access,
+	      scoped_user_rw_access_size;
+iterator scope;
+statement S;
+@@
+
+(
+(
+scoped_user_read_access(...) S
+|
+scoped_user_read_access_size(...) S
+|
+scoped_user_write_access(...) S
+|
+scoped_user_write_access_size(...) S
+|
+scoped_user_rw_access(...) S
+|
+scoped_user_rw_access_size(...) S
+)
+&
+scope(...) S
+)
+
+@script:python depends on r0 && report@
+@@
+print_mode = 'R'
+
+@script:python depends on r0 && org@
+@@
+print_mode = 'O'
+
+@r1@
+expression sp, a0, a1;
+iterator r0.scope;
+identifier ac;
+position p;
+@@
+
+  scope(sp,...) {
+    <...
+    ac@p(a0, a1, ...);
+    ...>
+  }
+
+@script:python@
+pos << r1.p;
+scope << r0.scope;
+ac << r1.ac;
+sp << r1.sp;
+a0 << r1.a0;
+a1 << r1.a1;
+@@
+
+scope = scopemap.get(scope, scope)
+if ac in noaccessmap.get(scope, []):
+   pr_err(pos, 'ERROR: Invalid access mode %s() in %s()' %(ac, scope))
+
+if ac in ptrmap:
+   ap = (a0, a1)[ptrmap[ac]]
+   if sp != ap.lstrip('&').split('->')[0].strip():
+      pr_err(pos, 'ERROR: Invalid pointer for %s(%s) in %s(%s)' %(ac, ap, scope, sp))