[PATCH 05/82] cocci: Refactor open-coded arithmetic wrap-around

[Kees Cook]

In pursuit of gaining full kernel instrumentation for signed[1],
unsigned[2], and pointer[3] arithmetic overflow, we need to replace
the handful of instances in the kernel where we intentionally depend on
arithmetic wrap-around. Introduce Coccinelle script for finding these
and replacing them with the new add_would_overflow() helper, for this
common code pattern:

	if (VAR + OFFSET < VAR) ...

Link: https://github.com/KSPP/linux/issues/26 [1]
Link: https://github.com/KSPP/linux/issues/27 [2]
Link: https://github.com/KSPP/linux/issues/344 [3]
Cc: Julia Lawall <Julia.Lawall@xxxxxxxx>
Cc: Nicolas Palix <nicolas.palix@xxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
Cc: cocci@xxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 .../coccinelle/misc/add_would_overflow.cocci  | 70 +++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 scripts/coccinelle/misc/add_would_overflow.cocci

diff --git a/scripts/coccinelle/misc/add_would_overflow.cocci b/scripts/coccinelle/misc/add_would_overflow.cocci
new file mode 100644
index 000000000000..b9b67c9c3714
--- /dev/null
+++ b/scripts/coccinelle/misc/add_would_overflow.cocci
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: GPL-2.0-only
+///
+/// Replace intentional wrap-around addition with calls to
+/// check_add_overflow() and add_would_overflow(), see
+/// Documentation/process/deprecated.rst
+///
+//
+// Confidence: High
+// Comments:
+// Options: --no-includes --include-headers
+
+virtual context
+virtual report
+virtual org
+virtual patch
+
+@report_wrap_sum depends on !patch@
+type RESULT;
+RESULT VAR;
+expression OFFSET;
+@@
+
+ {
+        RESULT sum;
+        ...
+        (
+*       VAR + OFFSET < VAR
+        )
+        ...
+        (
+        VAR + OFFSET
+        )
+        ...
+ }
+
+@wrap_sum depends on patch@
+type RESULT;
+RESULT VAR;
+expression OFFSET;
+@@
+
+ {
++       RESULT sum;
+        ...
+        (
+-       VAR + OFFSET < VAR
++       check_add_overflow(VAR, OFFSET, &sum)
+        )
+        ...
+        (
+-       VAR + OFFSET
++       sum
+        )
+        ...
+ }
+
+@report_wrap depends on !patch && !report_wrap_sum@
+identifier PTR;
+expression OFFSET;
+@@
+
+*       PTR + OFFSET < PTR
+
+@patch_wrap depends on patch && !wrap_sum@
+identifier PTR;
+expression OFFSET;
+@@
+
+-       PTR + OFFSET < PTR
++       add_would_overflow(PTR, OFFSET)
-- 
2.34.1