[PATCH v4 21/58] objtool/klp: Add test for rejecting module-owned static call keys

[Song Liu <song@kernel.org>]

From: Puranjay Mohan <puranjay@kernel.org>

Static calls carry the same constraint as static branches.  Check that a
vmlinux-owned key is accepted and a module-owned one is refused.

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
---
 .../tests/generic/fixtures/static_call.c      | 59 +++++++++++++++++++
 .../generic/test-static-call-module-key.sh    | 36 +++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 tools/objtool/tests/generic/fixtures/static_call.c
 create mode 100755 tools/objtool/tests/generic/test-static-call-module-key.sh

diff --git a/tools/objtool/tests/generic/fixtures/static_call.c b/tools/objtool/tests/generic/fixtures/static_call.c
new file mode 100644
index 000000000000..4a0c4c25321e
--- /dev/null
+++ b/tools/objtool/tests/generic/fixtures/static_call.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Static call site in a patched function, laid out by hand as for
+ * jump_label.c.  MODNAME selects whether the key belongs to vmlinux or a
+ * module.
+ *
+ * objtool's check pass would emit the site, and klp-write-tests.txt says to
+ * let it.  Not here: it does not emit the ANNOTATE_DATA_SPECIAL describing
+ * the entry boundaries -- in the kernel that comes from the static_call
+ * macros -- and NO_ANNOTATE below has to be able to take it away.  A fixture
+ * which varies the annotation has to write the entry that goes with it.
+ *
+ * NO_ANNOTATE drops the ANNOTATE_DATA_SPECIAL block from the patched build,
+ * leaving .static_call_sites with no annotation to describe its entry
+ * boundaries.  The section carries no entsize either, so klp diff has to fall
+ * back on the annotations it can still see -- and when the patched object is
+ * the only one that lost them, the two sides disagree about how the section is
+ * divided up.
+ *
+ * NEW_CALL puts the call site behind PATCHED, so the patch introduces one
+ * where the original had none.  The .static_call_sites entry is then new, with
+ * nothing in the original to correlate it against.
+ */
+
+#ifndef MODNAME
+#define MODNAME "vmlinux"
+#endif
+
+static const char __modinfo[]
+	__attribute__((section(".modinfo"), used, aligned(1))) = "\0name=" MODNAME;
+
+long __SCK__klp_test_call;
+
+int target(int x)
+{
+#if defined(NEW_CALL) && !defined(PATCHED)
+	/* The original has no static call at all. */
+	return x + 1;
+#else
+	__asm__ volatile(
+		"1:	nop\n\t"
+		".pushsection	.static_call_sites, \"aw\"\n\t"
+		".balign	8\n\t"
+		"912:\n\t"
+#if !(defined(PATCHED) && defined(NO_ANNOTATE))
+		".pushsection	.discard.annotate_data, \"M\", @progbits, 8\n\t"
+		".long		912b - ., 1\n\t"
+		".popsection\n\t"
+#endif
+		".long		1b - ., %c0 - .\n\t"
+		".popsection\n\t"
+		:: "i" (&__SCK__klp_test_call));
+#endif
+#ifdef PATCHED
+	return x + 2;
+#else
+	return x + 1;
+#endif
+}
diff --git a/tools/objtool/tests/generic/test-static-call-module-key.sh b/tools/objtool/tests/generic/test-static-call-module-key.sh
new file mode 100755
index 000000000000..260c4af72e05
--- /dev/null
+++ b/tools/objtool/tests/generic/test-static-call-module-key.sh
@@ -0,0 +1,36 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# As for static branches, a static call key owned by a module must be rejected
+# while a vmlinux-owned one is accepted.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair static_call.c
+
+has_input_section orig.o .static_call_sites ||
+	probe_skip "fixture produced no .static_call_sites on this arch"
+
+run_diff
+assert_patched target
+
+# The accepted half has to show the entry was carried, not just that the
+# function was: dropping the section silently would leave the patched call
+# unregistered, and "target was cloned" cannot tell the two apart.
+assert_section .static_call_sites
+assert_reloc_sym .static_call_sites target
+
+rm -f "$workdir/out.o"
+build_pair static_call.c -DMODNAME='"klp_testmod"'
+run_diff 255
+
+diff_log | grep -q 'unsupported static call key __SCK__klp_test_call' ||
+	fail "expected rejection, got: $(diff_log | tail -1)"
+
+# A rejection has to leave nothing behind.  out.o was removed above, so
+# anything here was written by the run which was supposed to refuse.
+[ -e "$workdir/out.o" ] &&
+	fail "output object produced for a rejected input"
+
+pass "module-owned static call key rejected, vmlinux-owned accepted"
-- 
2.53.0-Meta