This allows the patching to to emit 2 byte JMP/NOP instruction in addition to the 5 byte JMP/NOP we already did. This allows for more compact code.
This code is not yet used, as we don't emit shorter code at compile time yet. Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- arch/x86/include/asm/jump_label.h | 6 +- arch/x86/include/asm/nops.h | 1 arch/x86/kernel/jump_label.c | 77 +++++++++++++++++++++++--------------- 3 files changed, 53 insertions(+), 31 deletions(-) --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -7,9 +7,11 @@ #define JUMP_LABEL_NOP_SIZE 5 #ifdef CONFIG_X86_64 -# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC +# define STATIC_KEY_NOP2 P6_NOP2 +# define STATIC_KEY_NOP5 P6_NOP5_ATOMIC #else -# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC +# define STATIC_KEY_NOP2 GENERIC_NOP2 +# define STATIC_KEY_NOP5 GENERIC_NOP5_ATOMIC #endif #include <asm/asm.h> --- a/arch/x86/include/asm/nops.h +++ b/arch/x86/include/asm/nops.h @@ -5,6 +5,7 @@ /* * Define nops for use with alternative() and for tracing. * + * *_NOP2 must be a single instruction * *_NOP5_ATOMIC must be a single instruction. */ --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -17,49 +17,67 @@ #include <asm/text-patching.h> union jump_code_union { - char code[JUMP_LABEL_NOP_SIZE]; + char code[JMP32_INSN_SIZE]; struct { - char jump; - int offset; + char opcode; + union { + s8 d8; + s32 d32; + }; } __attribute__((packed)); }; -static void __jump_label_set_jump_code(struct jump_entry *entry, - enum jump_label_type type, - union jump_code_union *code, - int init) +static inline bool __jump_disp_is_byte(s32 disp) { - const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; - const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; - unsigned char *ip = (void *)jump_entry_code(entry); + return false; +} + +static int __jump_label_set_jump_code(struct jump_entry *entry, + enum jump_label_type type, + union jump_code_union *code, + int init) +{ + static unsigned char default_nop2[] = { STATIC_KEY_NOP2 }; + static unsigned char default_nop5[] = { STATIC_KEY_NOP5 }; + s32 disp = jump_entry_target(entry) - jump_entry_code(entry); + void *ip = (void *)jump_entry_code(entry); + const unsigned char *nop; const void *expect; - int line; + int line, size; - code->jump = 0xe9; - code->offset = jump_entry_target(entry) - - (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); - - if (init) { - expect = default_nop; line = __LINE__; - } else if (type == JUMP_LABEL_JMP) { - expect = ideal_nop; line = __LINE__; + if (__jump_disp_is_byte(disp)) { + size = JMP8_INSN_SIZE; + code->opcode = JMP8_INSN_OPCODE; + code->d8 = disp - size; + nop = init ? default_nop2 : ideal_nops[2]; + } else { + size = JMP32_INSN_SIZE; + code->opcode = JMP32_INSN_OPCODE; + code->d32 = disp - size; + nop = init ? default_nop5 : ideal_nops[NOP_ATOMIC5]; + } + + if (init || type == JUMP_LABEL_JMP) { + expect = nop; line = __LINE__; } else { expect = code->code; line = __LINE__; } - if (memcmp(ip, expect, JUMP_LABEL_NOP_SIZE)) { + if (memcmp(ip, expect, size)) { /* * The location is not an op that we were expecting. * Something went wrong. Crash the box, as something could be * corrupting the kernel. */ - pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) line:%d init:%d type:%d\n", - ip, ip, ip, expect, line, init, type); + pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) line:%d init:%d size:%d type:%d\n", + ip, ip, ip, expect, line, init, size, type); BUG(); } if (type == JUMP_LABEL_NOP) - memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE); + memcpy(code, nop, size); + + return size; } static void __ref __jump_label_transform(struct jump_entry *entry, @@ -67,8 +85,9 @@ static void __ref __jump_label_transform int init) { union jump_code_union code; + int size; - __jump_label_set_jump_code(entry, type, &code, init); + size = __jump_label_set_jump_code(entry, type, &code, init); /* * As long as only a single processor is running and the code is still @@ -82,12 +101,11 @@ static void __ref __jump_label_transform * always nop being the 'currently valid' instruction */ if (init || system_state == SYSTEM_BOOTING) { - text_poke_early((void *)jump_entry_code(entry), &code, - JUMP_LABEL_NOP_SIZE); + text_poke_early((void *)jump_entry_code(entry), &code, size); return; } - text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL); + text_poke_bp((void *)jump_entry_code(entry), &code, size, NULL); } void arch_jump_label_transform(struct jump_entry *entry, @@ -107,6 +125,7 @@ bool arch_jump_label_transform_queue(str { struct text_poke_loc *tp; void *entry_code; + int size; if (system_state == SYSTEM_BOOTING) { /* @@ -143,10 +162,10 @@ bool arch_jump_label_transform_queue(str return false; } - __jump_label_set_jump_code(entry, type, + size = __jump_label_set_jump_code(entry, type, (union jump_code_union *)&tp->text, 0); - text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL); + text_poke_loc_init(tp, entry_code, NULL, size, NULL); tp_vec_nr++;
