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From:   Ard Biesheuvel <ardb@kernel.org>
To:     linux-kernel@vger.kernel.org
Cc:     linux-arm-kernel@lists.infradead.org,
        Ard Biesheuvel <ardb@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jason Baron <jbaron@akamai.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Kees Cook <keescook@chromium.org>
Subject: [RFC PATCH 5/7] static_call: use non-function types to refer to the trampolines
Date:   Tue,  9 Nov 2021 17:45:47 +0100
Message-Id: <20211109164549.1724710-6-ardb@kernel.org>
In-Reply-To: <20211109164549.1724710-1-ardb@kernel.org>
References: <20211109164549.1724710-1-ardb@kernel.org>
MIME-Version: 1.0
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In order to prevent CFI enabled code from grabbing a jump table entry
that jumps to the trampoline, rather than the trampoline itself, use an
incomplete non-function type for the trampoline, and cast it to the
right type only when invoking it.

Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 include/linux/static_call.h             | 2 +-
 include/linux/static_call_types.h       | 6 +++---
 tools/include/linux/static_call_types.h | 6 +++---
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/static_call.h b/include/linux/static_call.h
index 391f737496eb..6b261fe96ba3 100644
--- a/include/linux/static_call.h
+++ b/include/linux/static_call.h
@@ -144,7 +144,7 @@ extern void arch_static_call_transform(void *site, void *tramp, void *func, bool
 
 #define static_call_update(name, func)					\
 ({									\
-	typeof(&STATIC_CALL_TRAMP(name)) __F = (func);			\
+	typeof(STATIC_CALL_QUERY(name)()) __F = (func);			\
 	__static_call_update(&STATIC_CALL_KEY(name),			\
 			     STATIC_CALL_TRAMP_ADDR(name), __F);	\
 })
diff --git a/include/linux/static_call_types.h b/include/linux/static_call_types.h
index 2fce9aa8a995..eae11c5b015d 100644
--- a/include/linux/static_call_types.h
+++ b/include/linux/static_call_types.h
@@ -47,7 +47,7 @@ struct static_call_site {
 	extern __weak struct static_call_key STATIC_CALL_KEY(name);	\
 	extern __weak struct static_call_key *STATIC_CALL_GETKEY(name)(void);\
 	extern __weak typeof(func) *STATIC_CALL_QUERY(name)(void);	\
-	extern typeof(func) STATIC_CALL_TRAMP(name)
+	extern struct static_call_tramp STATIC_CALL_TRAMP(name)
 
 #define __static_call_query(name)					\
 	((typeof(STATIC_CALL_QUERY(name)()))READ_ONCE(STATIC_CALL_KEY(name).func))
@@ -66,7 +66,7 @@ struct static_call_site {
 #define static_call(name)						\
 ({									\
 	__STATIC_CALL_ADDRESSABLE(name);				\
-	(&STATIC_CALL_TRAMP(name));					\
+	((typeof(STATIC_CALL_QUERY(name)()))&STATIC_CALL_TRAMP(name));	\
 })
 
 #ifdef CONFIG_HAVE_STATIC_CALL_INLINE
@@ -107,7 +107,7 @@ struct static_call_key {
 };
 
 #define static_call(name)						\
-	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+	((typeof(STATIC_CALL_QUERY(name)()))(STATIC_CALL_KEY(name).func))
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
diff --git a/tools/include/linux/static_call_types.h b/tools/include/linux/static_call_types.h
index 2fce9aa8a995..eae11c5b015d 100644
--- a/tools/include/linux/static_call_types.h
+++ b/tools/include/linux/static_call_types.h
@@ -47,7 +47,7 @@ struct static_call_site {
 	extern __weak struct static_call_key STATIC_CALL_KEY(name);	\
 	extern __weak struct static_call_key *STATIC_CALL_GETKEY(name)(void);\
 	extern __weak typeof(func) *STATIC_CALL_QUERY(name)(void);	\
-	extern typeof(func) STATIC_CALL_TRAMP(name)
+	extern struct static_call_tramp STATIC_CALL_TRAMP(name)
 
 #define __static_call_query(name)					\
 	((typeof(STATIC_CALL_QUERY(name)()))READ_ONCE(STATIC_CALL_KEY(name).func))
@@ -66,7 +66,7 @@ struct static_call_site {
 #define static_call(name)						\
 ({									\
 	__STATIC_CALL_ADDRESSABLE(name);				\
-	(&STATIC_CALL_TRAMP(name));					\
+	((typeof(STATIC_CALL_QUERY(name)()))&STATIC_CALL_TRAMP(name));	\
 })
 
 #ifdef CONFIG_HAVE_STATIC_CALL_INLINE
@@ -107,7 +107,7 @@ struct static_call_key {
 };
 
 #define static_call(name)						\
-	((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
+	((typeof(STATIC_CALL_QUERY(name)()))(STATIC_CALL_KEY(name).func))
 
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
-- 
2.30.2