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Commit c4b2c0c5 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by David S. Miller
Browse files

static_key: WARN on usage before jump_label_init was called 



Usage of the static key primitives to toggle a branch must not be used
before jump_label_init() is called from init/main.c. jump_label_init
reorganizes and wires up the jump_entries so usage before that could
have unforeseen consequences.

Following primitives are now checked for correct use:
* static_key_slow_inc
* static_key_slow_dec
* static_key_slow_dec_deferred
* jump_label_rate_limit

The x86 architecture already checks this by testing if the default_nop
was already replaced with an optimal nop or with a branch instruction. It
will panic then. Other architectures don't check for this.

Because we need to relax this check for the x86 arch to allow code to
transition from default_nop to the enabled state and other architectures
did not check for this at all this patch introduces checking on the
static_key primitives in a non-arch dependent manner.

All checked functions are considered slow-path so the additional check
does no harm to performance.

The warnings are best observed with earlyprintk.

Based on a patch from Andi Kleen.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b50026b5

include/linux/jump_label.h

+10 −0
Original line number Diff line number Diff line
@@ -48,6 +48,13 @@ 


#include <linux/types.h>

#include <linux/compiler.h>

#include <linux/bug.h>



extern bool static_key_initialized;



#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized,		      \

				    "%s used before call to jump_label_init", \

				    __func__)



#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
@@ -128,6 +135,7 @@ struct static_key { 


static __always_inline void jump_label_init(void)

{

	static_key_initialized = true;

}



static __always_inline bool static_key_false(struct static_key *key)
@@ -146,11 +154,13 @@ static __always_inline bool static_key_true(struct static_key *key) 


static inline void static_key_slow_inc(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();

	atomic_inc(&key->enabled);

}



static inline void static_key_slow_dec(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();

	atomic_dec(&key->enabled);

}

include/linux/jump_label_ratelimit.h

+2 −0
Original line number Diff line number Diff line
@@ -23,12 +23,14 @@ struct static_key_deferred { 
};

static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)

{

	STATIC_KEY_CHECK_USE();

	static_key_slow_dec(&key->key);

}

static inline void

jump_label_rate_limit(struct static_key_deferred *key,

		unsigned long rl)

{

	STATIC_KEY_CHECK_USE();

}

#endif	/* HAVE_JUMP_LABEL */

#endif	/* _LINUX_JUMP_LABEL_RATELIMIT_H */

init/main.c

+7 −0
Original line number Diff line number Diff line
@@ -135,6 +135,13 @@ static char *static_command_line; 
static char *execute_command;

static char *ramdisk_execute_command;



/*

 * Used to generate warnings if static_key manipulation functions are used

 * before jump_label_init is called.

 */

bool static_key_initialized __read_mostly = false;

EXPORT_SYMBOL_GPL(static_key_initialized);



/*

 * If set, this is an indication to the drivers that reset the underlying

 * device before going ahead with the initialization otherwise driver might

kernel/jump_label.c

+5 −0
Original line number Diff line number Diff line
@@ -58,6 +58,7 @@ static void jump_label_update(struct static_key *key, int enable); 


void static_key_slow_inc(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();

	if (atomic_inc_not_zero(&key->enabled))

		return;
@@ -103,12 +104,14 @@ static void jump_label_update_timeout(struct work_struct *work) 


void static_key_slow_dec(struct static_key *key)

{

	STATIC_KEY_CHECK_USE();

	__static_key_slow_dec(key, 0, NULL);

}

EXPORT_SYMBOL_GPL(static_key_slow_dec);



void static_key_slow_dec_deferred(struct static_key_deferred *key)

{

	STATIC_KEY_CHECK_USE();

	__static_key_slow_dec(&key->key, key->timeout, &key->work);

}

EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
@@ -116,6 +119,7 @@ EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred); 
void jump_label_rate_limit(struct static_key_deferred *key,

		unsigned long rl)

{

	STATIC_KEY_CHECK_USE();

	key->timeout = rl;

	INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);

}
@@ -212,6 +216,7 @@ void __init jump_label_init(void) 
		key->next = NULL;

#endif

	}

	static_key_initialized = true;

	jump_label_unlock();

}