x86/jump_table: Use relative references

Similar to the arm64 case, 64-bit x86 can benefit from using relative
references rather than absolute ones when emitting struct jump_entry
instances. Not only does this reduce the memory footprint of the entries
themselves by 33%, it also removes the need for carrying relocation
metadata on relocatable builds (i.e., for KASLR) which saves a fair
chunk of .init space as well (although the savings are not as dramatic
as on arm64)

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/20180919065144.25010-7-ard.biesheuvel@linaro.org

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1a0be02..603f374 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -119,6 +119,7 @@ config X86
        select HAVE_ARCH_AUDITSYSCALL
        select HAVE_ARCH_HUGE_VMAP              if X86_64 || X86_PAE
        select HAVE_ARCH_JUMP_LABEL
+       select HAVE_ARCH_JUMP_LABEL_RELATIVE
        select HAVE_ARCH_KASAN                  if X86_64
        select HAVE_ARCH_KGDB
        select HAVE_ARCH_MMAP_RND_BITS          if MMU

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 8c0de42..21efc9d 100644 (file)
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -37,7 +37,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
                ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
                ".pushsection __jump_table,  \"aw\" \n\t"
                _ASM_ALIGN "\n\t"
-               _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
+               ".long 1b - ., %l[l_yes] - . \n\t"
+               _ASM_PTR "%c0 + %c1 - .\n\t"
                ".popsection \n\t"
                : :  "i" (key), "i" (branch) : : l_yes);
 
@@ -53,7 +54,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
                "2:\n\t"
                ".pushsection __jump_table,  \"aw\" \n\t"
                _ASM_ALIGN "\n\t"
-               _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
+               ".long 1b - ., %l[l_yes] - . \n\t"
+               _ASM_PTR "%c0 + %c1 - .\n\t"
                ".popsection \n\t"
                : :  "i" (key), "i" (branch) : : l_yes);
 
@@ -62,18 +64,6 @@ l_yes:
        return true;
 }
 
-#ifdef CONFIG_X86_64
-typedef u64 jump_label_t;
-#else
-typedef u32 jump_label_t;
-#endif
-
-struct jump_entry {
-       jump_label_t code;
-       jump_label_t target;
-       jump_label_t key;
-};
-
 #else  /* __ASSEMBLY__ */
 
 .macro STATIC_JUMP_IF_TRUE target, key, def
@@ -88,7 +78,8 @@ struct jump_entry {
        .endif
        .pushsection __jump_table, "aw"
        _ASM_ALIGN
-       _ASM_PTR        .Lstatic_jump_\@, \target, \key
+       .long           .Lstatic_jump_\@ - ., \target - .
+       _ASM_PTR        \key - .
        .popsection
 .endm
 
@@ -104,7 +95,8 @@ struct jump_entry {
        .endif
        .pushsection __jump_table, "aw"
        _ASM_ALIGN
-       _ASM_PTR        .Lstatic_jump_\@, \target, \key + 1
+       .long           .Lstatic_jump_\@ - ., \target - .
+       _ASM_PTR        \key + 1 - .
        .popsection
 .endm
 

diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index 84f001d..50af4e1 100644 (file)
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -30,9 +30,9 @@
 #define EX_ORIG_OFFSET         0
 #define EX_NEW_OFFSET          4
 
-#define JUMP_ENTRY_SIZE                24
+#define JUMP_ENTRY_SIZE                16
 #define JUMP_ORIG_OFFSET       0
-#define JUMP_NEW_OFFSET                8
+#define JUMP_NEW_OFFSET                4
 
 #define ALT_ENTRY_SIZE         13
 #define ALT_ORIG_OFFSET                0