[PATCH v4 32/58] objtool/klp: Add test for EXPORT_SYMBOL_FOR_MODULES references

[Song Liu <song@kernel.org>]

A symbol exported with EXPORT_SYMBOL_FOR_MODULES() is reachable only by the
modules named in its namespace, and a livepatch module is never one of
them. So a reference to it cannot be an ordinary relocation resolved by the
module loader; it has to be a klp relocation applied at patch time.

Getting this wrong is silent.  The module links, loads, and reads the wrong
thing, or fails to load for a reason that does not name the cause.

This tests the behavior of commit 4cd3cfb8b54f ("objtool/klp: Fix
relocations for EXPORT_SYMBOL_FOR_MODULES() symbols").  Which object the
resulting relocation is filed under is a separate question, and one this
test cannot ask: the patched object here is vmlinux, so the vmlinux section
is the one produced either way.  That is covered by the module case, in
"objtool/klp: Add test for vmlinux relocs in a patched module".

Assisted-by: Claude:claude-opus-4
Based-on-test-by: Joe Lawrence <joe.lawrence@redhat.com>
Assisted-by: Claude:claude-opus-5
Signed-off-by: Song Liu <song@kernel.org>
---
 .../generic/test-export-symbol-for-modules.sh | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100755 tools/objtool/tests/generic/test-export-symbol-for-modules.sh

diff --git a/tools/objtool/tests/generic/test-export-symbol-for-modules.sh b/tools/objtool/tests/generic/test-export-symbol-for-modules.sh
new file mode 100755
index 000000000000..7e7bdde6a7ac
--- /dev/null
+++ b/tools/objtool/tests/generic/test-export-symbol-for-modules.sh
@@ -0,0 +1,39 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# EXPORT_SYMBOL_FOR_MODULES() puts a vmlinux symbol in a "module:<names>"
+# namespace, and the module loader grants access by matching the importing
+# module's name against that list.  A livepatch module is never on the list, so
+# referencing such a symbol with a normal relocation fails modpost, and if that
+# is silenced, fails to load with "Unknown symbol".  It needs a klp relocation,
+# the same as an unexported symbol.
+#
+# Ordinary namespaces are not affected: copy_import_ns() propagates the patched
+# object's import tags to the patch module, so a normal relocation works.
+
+. "$(dirname "$0")/../lib.sh"
+
+setup
+build_pair cross_module.c
+
+sym=other_mod_func
+
+# Plain vmlinux export: a normal relocation is what we want.
+export_syms "$sym"
+run_diff
+assert_no_klp_sym "$sym"
+
+# Ordinary namespace: still a normal relocation.
+export_syms
+add_exports_ns vmlinux MY_NS "$sym"
+run_diff
+assert_no_klp_sym "$sym"
+
+# module: namespace: has to become a klp relocation.
+export_syms
+add_exports_ns vmlinux module:kvm "$sym"
+run_diff
+assert_klp_sym "$sym" vmlinux
+assert_section __klp_relocs.vmlinux
+
+pass "EXPORT_SYMBOL_FOR_MODULES symbol referenced with a klp relocation"
-- 
2.53.0-Meta