[RFC PATCH 5/7] static_call: use non-function types to refer to the trampolines

Ard Biesheuvel
2021-11-09T16:46:28Z

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