[tip: objtool/core] objtool/klp: Add test for rejecting changed data

[tip-bot2 for Puranjay Mohan]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     6a73fa640753cbf93163771c7fc70b06a165de3e
Gitweb:        https://git.kernel.org/tip/6a73fa640753cbf93163771c7fc70b06a165de3e
Author:        Puranjay Mohan <puranjay@xxxxxxxxxx>
AuthorDate:    Wed, 16 Sep 2026 11:43:05 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 16 Sep 2026 17:13:27 -07:00

objtool/klp: Add test for rejecting changed data

Livepatching replaces functions.  Nothing can swap a variable which live
code already refers to, so a patch which changes one has to be refused
rather than applied with the old value left in place.

Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@xxxxxxxxxx>
Link: https://patch.msgid.link/20260916184351.2720310-13-song@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/tests/generic/fixtures/changed_data.c | 16 +++++++++++-
 tools/objtool/tests/generic/test-changed-data.sh    | 18 ++++++++++++-
 2 files changed, 34 insertions(+)
 create mode 100644 tools/objtool/tests/generic/fixtures/changed_data.c
 create mode 100755 tools/objtool/tests/generic/test-changed-data.sh

diff --git a/tools/objtool/tests/generic/fixtures/changed_data.c b/tools/objtool/tests/generic/fixtures/changed_data.c
new file mode 100644
index 0000000..b524618
--- /dev/null
+++ b/tools/objtool/tests/generic/fixtures/changed_data.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Data whose value differs between the two builds. */
+
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+
+#ifdef PATCHED
+int klp_test_data = 2;
+#else
+int klp_test_data = 1;
+#endif
+
+int target(int x)
+{
+	return x + klp_test_data;
+}
diff --git a/tools/objtool/tests/generic/test-changed-data.sh b/tools/objtool/tests/generic/test-changed-data.sh
new file mode 100755
index 0000000..c5c7381
--- /dev/null
+++ b/tools/objtool/tests/generic/test-changed-data.sh
@@ -0,0 +1,18 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Livepatching replaces functions, not data.  A changed data symbol must be
+# rejected.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair changed_data.c
+run_diff 255
+
+diff_log | grep -q 'changed data: klp_test_data' ||
+	fail "expected rejection, got: $(diff_log | tail -1)"
+[ -e "$workdir/out.o" ] &&
+	fail "output object produced for a rejected input"
+
+pass "changed data symbol rejected"