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static_call: Allow module use without exposing static_call_key

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When exporting static_call_key; with EXPORT_STATIC_CALL*(), the module
can use static_call_update() to change the function called.  This is
not desirable in general.

Not exporting static_call_key however also disallows usage of
static_call(), since objtool needs the key to construct the
static_call_site.

Solve this by allowing objtool to create the static_call_site using
the trampoline address when it builds a module and cannot find the
static_call_key symbol. The module loader will then try and map the
trampole back to a key before it constructs the normal sites list.

Doing this requires a trampoline -> key associsation, so add another
magic section that keeps those.

Originally-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210127231837.ifddpn7rhwdaepiu@treble
This commit is contained in:
Josh Poimboeuf
2021-01-27 17:18:37 -06:00
committed by Ingo Molnar
parent e59e10f8ef
commit 73f44fe19d
7 changed files with 149 additions and 11 deletions
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22
include/linux/static_call.h
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@@ -138,6 +138,12 @@ struct static_call_key {
};
};
/* For finding the key associated with a trampoline */
struct static_call_tramp_key {
s32 tramp;
s32 key;
};
extern void __static_call_update(struct static_call_key *key, void *tramp, void *func);
extern int static_call_mod_init(struct module *mod);
extern int static_call_text_reserved(void *start, void *end);
@@ -165,11 +171,18 @@ extern long __static_call_return0(void);
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
/* Leave the key unexported, so modules can't change static call targets: */
#define EXPORT_STATIC_CALL_TRAMP(name) \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name)); \
ARCH_ADD_TRAMP_KEY(name)
#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name)); \
ARCH_ADD_TRAMP_KEY(name)
#elif defined(CONFIG_HAVE_STATIC_CALL)
static inline int static_call_init(void) { return 0; }
@@ -216,11 +229,16 @@ static inline long __static_call_return0(void)
#define EXPORT_STATIC_CALL(name) \
EXPORT_SYMBOL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name)); \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
/* Leave the key unexported, so modules can't change static call targets: */
#define EXPORT_STATIC_CALL_TRAMP(name) \
EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))
#define EXPORT_STATIC_CALL_TRAMP_GPL(name) \
EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(name))
#else /* Generic implementation */
static inline int static_call_init(void) { return 0; }