Commit 73f44fe1 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

static_call: Allow module use without exposing static_call_key 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210127231837.ifddpn7rhwdaepiu@treble
parent e59e10f8

arch/x86/include/asm/static_call.h

+7 −0
Original line number Original line Diff line number Diff line
@@ -37,4 +37,11 @@ 
#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\

#define ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)			\

	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")

	__ARCH_DEFINE_STATIC_CALL_TRAMP(name, "ret; nop; nop; nop; nop")







#define ARCH_ADD_TRAMP_KEY(name)					\

	asm(".pushsection .static_call_tramp_key, \"a\"		\n"	\

	    ".long " STATIC_CALL_TRAMP_STR(name) " - .		\n"	\

	    ".long " STATIC_CALL_KEY_STR(name) " - .		\n"	\

	    ".popsection					\n")



#endif /* _ASM_STATIC_CALL_H */
 
#endif /* _ASM_STATIC_CALL_H */

include/asm-generic/vmlinux.lds.h

+4 −1
Original line number Original line Diff line number Diff line
@@ -393,7 +393,10 @@ 
	. = ALIGN(8);							\

	. = ALIGN(8);							\

	__start_static_call_sites = .;					\

	__start_static_call_sites = .;					\

	KEEP(*(.static_call_sites))					\

	KEEP(*(.static_call_sites))					\

	__stop_static_call_sites = .;

	__stop_static_call_sites = .;					\

	__start_static_call_tramp_key = .;				\

	KEEP(*(.static_call_tramp_key))					\

	__stop_static_call_tramp_key = .;





/*

/*

 * Allow architectures to handle ro_after_init data on their

 * Allow architectures to handle ro_after_init data on their

include/linux/static_call.h

+20 −2
Original line number Original line Diff line number Diff line
@@ -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 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_mod_init(struct module *mod);

extern int static_call_text_reserved(void *start, void *end);

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)					\

#define EXPORT_STATIC_CALL(name)					\

	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\

	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\

	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))

	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))



#define EXPORT_STATIC_CALL_GPL(name)					\

#define EXPORT_STATIC_CALL_GPL(name)					\

	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));			\

	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));			\

	EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(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)

#elif defined(CONFIG_HAVE_STATIC_CALL)





static inline int static_call_init(void) { return 0; }

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)					\

#define EXPORT_STATIC_CALL(name)					\

	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\

	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\

	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))

	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))



#define EXPORT_STATIC_CALL_GPL(name)					\

#define EXPORT_STATIC_CALL_GPL(name)					\

	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));			\

	EXPORT_SYMBOL_GPL(STATIC_CALL_KEY(name));			\

	EXPORT_SYMBOL_GPL(STATIC_CALL_TRAMP(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 */

#else /* Generic implementation */





static inline int static_call_init(void) { return 0; }

static inline int static_call_init(void) { return 0; }

include/linux/static_call_types.h

+25 −2
Original line number Original line Diff line number Diff line
@@ -10,6 +10,7 @@ 
#define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

#define STATIC_CALL_KEY_PREFIX_STR	__stringify(STATIC_CALL_KEY_PREFIX)

#define STATIC_CALL_KEY_PREFIX_LEN	(sizeof(STATIC_CALL_KEY_PREFIX_STR) - 1)

#define STATIC_CALL_KEY_PREFIX_LEN	(sizeof(STATIC_CALL_KEY_PREFIX_STR) - 1)

#define STATIC_CALL_KEY(name)		__PASTE(STATIC_CALL_KEY_PREFIX, name)

#define STATIC_CALL_KEY(name)		__PASTE(STATIC_CALL_KEY_PREFIX, name)

#define STATIC_CALL_KEY_STR(name)	__stringify(STATIC_CALL_KEY(name))





#define STATIC_CALL_TRAMP_PREFIX	__SCT__

#define STATIC_CALL_TRAMP_PREFIX	__SCT__

#define STATIC_CALL_TRAMP_PREFIX_STR	__stringify(STATIC_CALL_TRAMP_PREFIX)

#define STATIC_CALL_TRAMP_PREFIX_STR	__stringify(STATIC_CALL_TRAMP_PREFIX)
@@ -39,17 +40,39 @@ struct static_call_site { 




#ifdef CONFIG_HAVE_STATIC_CALL

#ifdef CONFIG_HAVE_STATIC_CALL





#define __raw_static_call(name)	(&STATIC_CALL_TRAMP(name))



#ifdef CONFIG_HAVE_STATIC_CALL_INLINE



/*

/*

 * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from

 * __ADDRESSABLE() is used to ensure the key symbol doesn't get stripped from

 * the symbol table so that objtool can reference it when it generates the

 * the symbol table so that objtool can reference it when it generates the

 * .static_call_sites section.

 * .static_call_sites section.

 */

 */

#define __STATIC_CALL_ADDRESSABLE(name) \

	__ADDRESSABLE(STATIC_CALL_KEY(name))



#define __static_call(name)						\

#define __static_call(name)						\

({									\

({									\

	__ADDRESSABLE(STATIC_CALL_KEY(name));				\

	__STATIC_CALL_ADDRESSABLE(name);				\

	&STATIC_CALL_TRAMP(name);					\

	__raw_static_call(name);					\

})

})





#else /* !CONFIG_HAVE_STATIC_CALL_INLINE */



#define __STATIC_CALL_ADDRESSABLE(name)

#define __static_call(name)	__raw_static_call(name)



#endif /* CONFIG_HAVE_STATIC_CALL_INLINE */



#ifdef MODULE

#define __STATIC_CALL_MOD_ADDRESSABLE(name)

#define static_call_mod(name)	__raw_static_call(name)

#else

#define __STATIC_CALL_MOD_ADDRESSABLE(name) __STATIC_CALL_ADDRESSABLE(name)

#define static_call_mod(name)	__static_call(name)

#endif



#define static_call(name)	__static_call(name)

#define static_call(name)	__static_call(name)





#else

#else

kernel/static_call.c

+53 −2
Original line number Original line Diff line number Diff line
@@ -12,6 +12,8 @@ 




extern struct static_call_site __start_static_call_sites[],

extern struct static_call_site __start_static_call_sites[],

			       __stop_static_call_sites[];

			       __stop_static_call_sites[];

extern struct static_call_tramp_key __start_static_call_tramp_key[],

				    __stop_static_call_tramp_key[];





static bool static_call_initialized;

static bool static_call_initialized;
@@ -323,10 +325,59 @@ static int __static_call_mod_text_reserved(void *start, void *end) 
	return ret;

	return ret;

}

}





static unsigned long tramp_key_lookup(unsigned long addr)

{

	struct static_call_tramp_key *start = __start_static_call_tramp_key;

	struct static_call_tramp_key *stop = __stop_static_call_tramp_key;

	struct static_call_tramp_key *tramp_key;



	for (tramp_key = start; tramp_key != stop; tramp_key++) {

		unsigned long tramp;



		tramp = (long)tramp_key->tramp + (long)&tramp_key->tramp;

		if (tramp == addr)

			return (long)tramp_key->key + (long)&tramp_key->key;

	}



	return 0;

}



static int static_call_add_module(struct module *mod)

static int static_call_add_module(struct module *mod)

{

{

	return __static_call_init(mod, mod->static_call_sites,

	struct static_call_site *start = mod->static_call_sites;

				  mod->static_call_sites + mod->num_static_call_sites);

	struct static_call_site *stop = start + mod->num_static_call_sites;

	struct static_call_site *site;



	for (site = start; site != stop; site++) {

		unsigned long addr = (unsigned long)static_call_key(site);

		unsigned long key;



		/*

		 * Is the key is exported, 'addr' points to the key, which

		 * means modules are allowed to call static_call_update() on

		 * it.

		 *

		 * Otherwise, the key isn't exported, and 'addr' points to the

		 * trampoline so we need to lookup the key.

		 *

		 * We go through this dance to prevent crazy modules from

		 * abusing sensitive static calls.

		 */

		if (!kernel_text_address(addr))

			continue;



		key = tramp_key_lookup(addr);

		if (!key) {

			pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",

				static_call_addr(site));

			return -EINVAL;

		}



		site->key = (key - (long)&site->key) |

			    (site->key & STATIC_CALL_SITE_FLAGS);

	}



	return __static_call_init(mod, start, stop);

}

}





static void static_call_del_module(struct module *mod)

static void static_call_del_module(struct module *mod)