linux-kernel - [RFC PATCH 7/7] static_call: add generic support for non-exported keys

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Message-Id: <20211109164549.1724710-8-ardb@kernel.org>
Date:   Tue,  9 Nov 2021 17:45:49 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>
Subject: [RFC PATCH 7/7] static_call: add generic support for non-exported keys

The static_call feature where only the static call target is exposed to
modules while access to the key is withheld is only implemented for the
inline and out-of-line varieties, but not for the generic indirect call
based variety.

Let's use static_call_query() to obtain the call target address if the
key is not exported. Note that this means we can do the converse as
well, i.e., implement static_call_query() in terms of the key struct if
the key is exported, so we only need to export one of the two.

Note that this adds an additional load and potentially a direct call to
the instantiations of static_call residing in module code.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 include/linux/static_call.h             | 4 ++--
 include/linux/static_call_types.h       | 3 +--
 tools/include/linux/static_call_types.h | 3 +--
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index 21929147879a..d88fd613f06d 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -302,8 +302,8 @@ static inline int static_call_text_reserved(void *start, void *end)
 	return 0;
 }
 
-#define EXPORT_STATIC_CALL(name)	EXPORT_SYMBOL(STATIC_CALL_KEY(name))
-#define EXPORT_STATIC_CALL_GPL(name)	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name))
+#define EXPORT_STATIC_CALL(name)	EXPORT_STATIC_CALL_QUERY(name,)
+#define EXPORT_STATIC_CALL_GPL(name)	EXPORT_STATIC_CALL_QUERY(name, _GPL)
 
 #define EXPORT_STATIC_CALL_FOR_UPDATE(name)	EXPORT_SYMBOL(STATIC_CALL_KEY(name))
 #define EXPORT_STATIC_CALL_FOR_UPDATE_GPL(name)	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name))
diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h
index eae11c5b015d..920828ad1d69 100644
--- a/include/linux/static_call_types.h
+++ b/include/linux/static_call_types.h
@@ -106,8 +106,7 @@ struct static_call_key {
 	void *func;
 };
 
-#define static_call(name)						\
-	((typeof(STATIC_CALL_QUERY(name)()))(STATIC_CALL_KEY(name).func))
+#define static_call(name)	static_call_query(name)
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
diff --git a/tools/include/linux/static_call_types.h b/tools/include/linux/static_call_types.h
index eae11c5b015d..920828ad1d69 100644
--- a/tools/include/linux/static_call_types.h
+++ b/tools/include/linux/static_call_types.h
@@ -106,8 +106,7 @@ struct static_call_key {
 	void *func;
 };
 
-#define static_call(name)						\
-	((typeof(STATIC_CALL_QUERY(name)()))(STATIC_CALL_KEY(name).func))
+#define static_call(name)	static_call_query(name)
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
-- 
2.30.2