[tip: objtool/core] objtool/klp: Add test for rejecting references to init code/data

[tip-bot2 for Puranjay Mohan]

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

Commit-ID:     f5e03560bd71922003384a2e24154b1d08bead1c
Gitweb:        https://git.kernel.org/tip/f5e03560bd71922003384a2e24154b1d08bead1c
Author:        Puranjay Mohan <puranjay@xxxxxxxxxx>
AuthorDate:    Wed, 16 Sep 2026 11:43:16 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 16 Sep 2026 17:13:28 -07:00

objtool/klp: Add test for rejecting references to init code/data

Init code and data are freed once boot finishes, so a klp relocation
against them can never resolve.

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/20260916184351.2720310-24-song@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/tests/generic/fixtures/init_reference.c | 17 ++++++-
 tools/objtool/tests/generic/test-init-reference.sh    | 29 ++++++++++-
 2 files changed, 46 insertions(+)
 create mode 100644 tools/objtool/tests/generic/fixtures/init_reference.c
 create mode 100755 tools/objtool/tests/generic/test-init-reference.sh

diff --git a/tools/objtool/tests/generic/fixtures/init_reference.c b/tools/objtool/tests/generic/fixtures/init_reference.c
new file mode 100644
index 0000000..9e59bdf
--- /dev/null
+++ b/tools/objtool/tests/generic/fixtures/init_reference.c
@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Patched function referencing data in an .init section. */
+
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=vmlinux";
+
+/* volatile so the read cannot be folded into a constant, leaving no reference */
+static volatile int init_only __attribute__((section(".init.data"), used)) = 5;
+
+int target(int x)
+{
+#ifdef PATCHED
+	return x + init_only + 1;
+#else
+	return x + init_only;
+#endif
+}
diff --git a/tools/objtool/tests/generic/test-init-reference.sh b/tools/objtool/tests/generic/test-init-reference.sh
new file mode 100755
index 0000000..921cf49
--- /dev/null
+++ b/tools/objtool/tests/generic/test-init-reference.sh
@@ -0,0 +1,29 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Init code and data are freed after boot, so a klp relocation against them can
+# never resolve.  Such a patch must be rejected.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair init_reference.c
+
+# The rejection can only happen if the patched build really does reference the
+# init symbol.  The fixture makes init_only volatile so the read cannot be
+# folded away, and this checks that it worked: without a relocation klp diff
+# would succeed, and the failure below would read as a missing check rather
+# than as a fixture which stopped posing the question.
+# Either spelling will do.  A file-local variable is reached through its
+# section symbol -- .init.data -- and a global one by name; which of the two
+# the compiler picks is its business, and the reference is what matters.
+in_relocs "$patched_obj" |
+	awk '$5 == ".init.data" || $5 == "init_only"' | grep -q . ||
+	fail "patched object has no reference into .init.data; the fixture tests nothing"
+
+run_diff 255
+
+diff_log | grep -q "can't patch or reference init code/data" ||
+	fail "expected rejection, got: $(diff_log | tail -1)"
+
+pass "reference to init data rejected"