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: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter 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

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 2eadff9b3b90..2768a925bafa 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -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;