[RFC PATCH tip/master V3 8/8] kprobes/x86: Consolidate insn decoder users for copying code

[Masami Hiramatsu]

Consolidate x86 instruction decoder users on the path of
copying original code for kprobes.

Kprobes decodes same instruction 3 times in maximum when
preparing instruction buffer. The first time for getting the
length of instruction, the 2nd for adjusting displacement,
and the 3rd for checking whether the instruction is boostable
or not. For each time, actually decoding target address is
slightly different (1st is original address or recovered
instruction buffer, 2nd and 3rd are copied buffer), but
basically those must have same instruction.
Thus, this patch also changes the target address to copied
buffer at first and reuses the decoded "insn" for displacement
adjusting and checking boostable.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 Changes in v2:
   - Fix several build errors.
---
 arch/x86/kernel/kprobes/common.h |    4 +-
 arch/x86/kernel/kprobes/core.c   |   66 ++++++++++++++++++--------------------
 arch/x86/kernel/kprobes/opt.c    |    5 ++-
 3 files changed, 36 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/kprobes/common.h b/arch/x86/kernel/kprobes/common.h
index d688826..db2182d 100644
--- a/arch/x86/kernel/kprobes/common.h
+++ b/arch/x86/kernel/kprobes/common.h
@@ -67,7 +67,7 @@
 #endif
 
 /* Ensure if the instruction can be boostable */
-extern int can_boost(kprobe_opcode_t *instruction, void *addr);
+extern int can_boost(struct insn *insn, void *orig_addr);
 /* Recover instruction if given address is probed */
 extern unsigned long recover_probed_instruction(kprobe_opcode_t *buf,
 					 unsigned long addr);
@@ -75,7 +75,7 @@ extern unsigned long recover_probed_instruction(kprobe_opcode_t *buf,
  * Copy an instruction and adjust the displacement if the instruction
  * uses the %rip-relative addressing mode.
  */
-extern int __copy_instruction(u8 *dest, u8 *src);
+extern int __copy_instruction(u8 *dest, u8 *src, struct insn *insn);
 
 /* Generate a relative-jump/call instruction */
 extern void synthesize_reljump(void *from, void *to);
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 722f544..19e1f2a 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -164,33 +164,29 @@ static kprobe_opcode_t *skip_prefixes(kprobe_opcode_t *insn)
 NOKPROBE_SYMBOL(skip_prefixes);
 
 /*
- * Returns non-zero if opcode is boostable.
+ * Returns non-zero if INSN is boostable.
  * RIP relative instructions are adjusted at copying time in 64 bits mode
  */
-int can_boost(kprobe_opcode_t *opcodes, void *addr)
+int can_boost(struct insn *insn, void *addr)
 {
-	struct insn insn;
 	kprobe_opcode_t opcode;
 
 	if (search_exception_tables((unsigned long)addr))
 		return 0;	/* Page fault may occur on this address. */
 
-	kernel_insn_init(&insn, (void *)opcodes, MAX_INSN_SIZE);
-	insn_get_opcode(&insn);
-
 	/* 2nd-byte opcode */
-	if (insn.opcode.nbytes == 2)
-		return test_bit(insn.opcode.bytes[1],
+	if (insn->opcode.nbytes == 2)
+		return test_bit(insn->opcode.bytes[1],
 				(unsigned long *)twobyte_is_boostable);
 
-	if (insn.opcode.nbytes != 1)
+	if (insn->opcode.nbytes != 1)
 		return 0;
 
 	/* Can't boost Address-size override prefix */
-	if (unlikely(inat_is_address_size_prefix(insn.attr)))
+	if (unlikely(inat_is_address_size_prefix(insn->attr)))
 		return 0;
 
-	opcode = insn.opcode.bytes[0];
+	opcode = insn->opcode.bytes[0];
 
 	switch (opcode & 0xf0) {
 	case 0x60:
@@ -351,35 +347,31 @@ static int is_IF_modifier(kprobe_opcode_t *insn)
  * addressing mode.
  * This returns the length of copied instruction, or 0 if it has an error.
  */
-int __copy_instruction(u8 *dest, u8 *src)
+int __copy_instruction(u8 *dest, u8 *src, struct insn *insn)
 {
-	struct insn insn;
 	kprobe_opcode_t buf[MAX_INSN_SIZE];
-	int length;
 	unsigned long recovered_insn =
 		recover_probed_instruction(buf, (unsigned long)src);
 
-	if (!recovered_insn)
+	if (!recovered_insn || !insn)
 		return 0;
-	kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
-	insn_get_length(&insn);
-	length = insn.length;
 
-	/* Another subsystem puts a breakpoint, failed to recover */
-	if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
+	/* This can access kernel text if given address is not recovered */
+	if (probe_kernel_read(dest, (void *)recovered_insn, MAX_INSN_SIZE))
 		return 0;
 
-	/* This can access kernel text if given address is not recovered */
-	if (kernel_probe_read(dest, insn.kaddr, length))
+	kernel_insn_init(insn, dest, MAX_INSN_SIZE);
+	insn_get_length(insn);
+
+	/* Another subsystem puts a breakpoint, failed to recover */
+	if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 		return 0;
 
 #ifdef CONFIG_X86_64
 	/* Only x86_64 has RIP relative instructions */
-	if (insn_rip_relative(&insn)) {
+	if (insn_rip_relative(insn)) {
 		s64 newdisp;
 		u8 *disp;
-		kernel_insn_init(&insn, dest, length);
-		insn_get_displacement(&insn);
 		/*
 		 * The copied instruction uses the %rip-relative addressing
 		 * mode.  Adjust the displacement for the difference between
@@ -392,29 +384,32 @@ int __copy_instruction(u8 *dest, u8 *src)
 		 * extension of the original signed 32-bit displacement would
 		 * have given.
 		 */
-		newdisp = (u8 *) src + (s64) insn.displacement.value - (u8 *) dest;
+		newdisp = (u8 *) src + (s64) insn->displacement.value
+			  - (u8 *) dest;
 		if ((s64) (s32) newdisp != newdisp) {
 			pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
-			pr_err("\tSrc: %p, Dest: %p, old disp: %x\n", src, dest, insn.displacement.value);
+			pr_err("\tSrc: %p, Dest: %p, old disp: %x\n",
+				src, dest, insn->displacement.value);
 			return 0;
 		}
-		disp = (u8 *) dest + insn_offset_displacement(&insn);
+		disp = (u8 *) dest + insn_offset_displacement(insn);
 		*(s32 *) disp = (s32) newdisp;
 	}
 #endif
-	return length;
+	return insn->length;
 }
 
 /* Prepare reljump right after instruction to boost */
-static void prepare_boost(struct kprobe *p, int length)
+static void prepare_boost(struct kprobe *p, struct insn *insn)
 {
-	if (can_boost(p->ainsn.insn, p->addr) &&
-	    MAX_INSN_SIZE - length >= RELATIVEJUMP_SIZE) {
+	if (can_boost(insn, p->addr) &&
+	    MAX_INSN_SIZE - insn->length >= RELATIVEJUMP_SIZE) {
 		/*
 		 * These instructions can be executed directly if it
 		 * jumps back to correct address.
 		 */
-		synthesize_reljump(p->ainsn.insn + length, p->addr + length);
+		synthesize_reljump(p->ainsn.insn + insn->length,
+				   p->addr + insn->length);
 		p->ainsn.boostable = true;
 	} else {
 		p->ainsn.boostable = false;
@@ -423,12 +418,13 @@ static void prepare_boost(struct kprobe *p, int length)
 
 static int arch_copy_kprobe(struct kprobe *p)
 {
+	struct insn insn;
 	int len;
 
 	set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
 
 	/* Copy an instruction with recovering if other optprobe modifies it.*/
-	len = __copy_instruction(p->ainsn.insn, p->addr);
+	len = __copy_instruction(p->ainsn.insn, p->addr, &insn);
 	if (!len)
 		return -EINVAL;
 
@@ -436,7 +432,7 @@ static int arch_copy_kprobe(struct kprobe *p)
 	 * __copy_instruction can modify the displacement of the instruction,
 	 * but it doesn't affect boostable check.
 	 */
-	prepare_boost(p, len);
+	prepare_boost(p, &insn);
 
 	set_memory_ro((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
 
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 5b52334..9aadff3 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -177,11 +177,12 @@ NOKPROBE_SYMBOL(optimized_callback);
 
 static int copy_optimized_instructions(u8 *dest, u8 *src)
 {
+	struct insn insn;
 	int len = 0, ret;
 
 	while (len < RELATIVEJUMP_SIZE) {
-		ret = __copy_instruction(dest + len, src + len);
-		if (!ret || !can_boost(dest + len, src + len))
+		ret = __copy_instruction(dest + len, src + len, &insn);
+		if (!ret || !can_boost(&insn, src + len))
 			return -EINVAL;
 		len += ret;
 	}