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jump_label: Implement generic support for relative references

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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: Ard Biesheuvel <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Arnd Bergmann <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Jessica Yu <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
This commit is contained in:
Ard Biesheuvel 2018-09-18 23:51:37 -07:00 • committed by Thomas Gleixner
commit 50ff18ab49
3 changed files with 52 additions and 1 deletions
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3
arch/Kconfig
View file

@ -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

28
include/linux/jump_label.h
View file

@ -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;

22
kernel/jump_label.c
View file

@ -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);