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Date: Fri, 28 Jun 2019 12:21:19 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org, peterz@...radead.org, linux-kernel@...r.kernel.org
Cc: Josh Poimboeuf <jpoimboe@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Jason Baron <jbaron@...mai.com>, Nadav Amit <namit@...are.com>,
Andy Lutomirski <luto@...nel.org>,
Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [RFC][PATCH 6/8] jump_label, x86: Add variable length patching support
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) <peterz@...radead.org>
---
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++;
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