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

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
......@@ -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);
}
......
......@@ -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 */
......@@ -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
......
......@@ -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();
}
......
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