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.law...@inria.fr>
Cc: Nicolas Palix <nicolas.pa...@imag.fr>
Cc: "Gustavo A. R. Silva" <gustavo...@kernel.org>
Cc: Justin Stitt <justinst...@google.com>
Cc: co...@inria.fr
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
.../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
