Commit 50ff18ab authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Thomas Gleixner
Browse files

jump_label: Implement generic support for relative references 



To reduce the size taken up by absolute references in jump label
entries themselves and the associated relocation records in the
.init segment, add support for emitting them as relative references
instead.

Note that this requires some extra care in the sorting routine, given
that the offsets change when entries are moved around in the jump_entry
table.

Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-s390@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jessica Yu <jeyu@kernel.org>
Link: https://lkml.kernel.org/r/20180919065144.25010-3-ard.biesheuvel@linaro.org
parent 9ae033ac

arch/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -359,6 +359,9 @@ config HAVE_PERF_USER_STACK_DUMP 
config HAVE_ARCH_JUMP_LABEL

	bool



config HAVE_ARCH_JUMP_LABEL_RELATIVE

	bool



config HAVE_RCU_TABLE_FREE

	bool

include/linux/jump_label.h

+28 −0
Original line number Diff line number Diff line
@@ -121,6 +121,32 @@ struct static_key { 
#include <asm/jump_label.h>



#ifndef __ASSEMBLY__

#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE



struct jump_entry {

	s32 code;

	s32 target;

	long key;	// key may be far away from the core kernel under KASLR

};



static inline unsigned long jump_entry_code(const struct jump_entry *entry)

{

	return (unsigned long)&entry->code + entry->code;

}



static inline unsigned long jump_entry_target(const struct jump_entry *entry)

{

	return (unsigned long)&entry->target + entry->target;

}



static inline struct static_key *jump_entry_key(const struct jump_entry *entry)

{

	long offset = entry->key & ~1L;



	return (struct static_key *)((unsigned long)&entry->key + offset);

}



#else



static inline unsigned long jump_entry_code(const struct jump_entry *entry)

{
@@ -137,6 +163,8 @@ static inline struct static_key *jump_entry_key(const struct jump_entry *entry) 
	return (struct static_key *)((unsigned long)entry->key & ~1UL);

}



#endif



static inline bool jump_entry_is_branch(const struct jump_entry *entry)

{

	return (unsigned long)entry->key & 1UL;

kernel/jump_label.c

+21 −1
Original line number Diff line number Diff line
@@ -47,14 +47,34 @@ static int jump_label_cmp(const void *a, const void *b) 
	return 0;

}



static void jump_label_swap(void *a, void *b, int size)

{

	long delta = (unsigned long)a - (unsigned long)b;

	struct jump_entry *jea = a;

	struct jump_entry *jeb = b;

	struct jump_entry tmp = *jea;



	jea->code	= jeb->code - delta;

	jea->target	= jeb->target - delta;

	jea->key	= jeb->key - delta;



	jeb->code	= tmp.code + delta;

	jeb->target	= tmp.target + delta;

	jeb->key	= tmp.key + delta;

}



static void

jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)

{

	unsigned long size;

	void *swapfn = NULL;



	if (IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE))

		swapfn = jump_label_swap;



	size = (((unsigned long)stop - (unsigned long)start)

					/ sizeof(struct jump_entry));

	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);

	sort(start, size, sizeof(struct jump_entry), jump_label_cmp, swapfn);

}



static void jump_label_update(struct static_key *key);

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