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[PATCH] kprobe: kprobe-2byte-booster


Hi,

Here is a patch of kprobe-booster enhancement on i386
This patch can be applied to 2.6.17-rc1.

Previous kprobe-booster patch has not handled any 2byte opcodes
and prefixes. I checked whole IA32 opcode map and classified it.

This patch enables kprobe to boost those 2byte opcodes and prefixes.

Best regards,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: hiramatu@sdl.hitachi.co.jp


 kprobes.c |   63 +++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 50 insertions(+), 13 deletions(-)
diff -Narup a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
--- a/arch/i386/kernel/kprobes.c	2006-04-03 18:30:59.000000000 +0900
+++ b/arch/i386/kernel/kprobes.c	2006-04-03 19:41:54.000000000 +0900
@@ -55,32 +55,69 @@ static inline void set_jmp_op(void *from
 }

 /*
+ * Undefined/reserved opcodes, conditional jump, Opcode Extension Groups,
+ * and some special opcodes can not be boost.
+ */
+static char boostable_2nd_opcode[256] = {
+0,0,1,1,0,0,1,0,1,1,0,0,0,0,0,0,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,
+0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+1,1,1,1,1,1,1,1,1,1,1,1,0,0,1,1,
+0,0,0,0,1,1,1,1,0,0,0,0,0,0,1,1,
+0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+1,1,0,1,1,1,0,0,1,1,0,1,1,1,0,1,
+1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1,
+1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1,
+0,1,1,1,0,1,0,0,1,1,0,1,1,1,0,1,
+0,1,1,0,0,1,0,0,1,1,0,1,1,1,0,1,
+0,1,1,1,0,1,0,0,1,1,1,0,1,1,1,0
+};
+
+/*
  * returns non-zero if opcodes can be boosted.
  */
-static inline int can_boost(kprobe_opcode_t opcode)
+static inline int can_boost(kprobe_opcode_t *opcodes)
 {
-	switch (opcode & 0xf0 ) {
+	kprobe_opcode_t opcode;
+	kprobe_opcode_t *orig_opcodes = opcodes;
+retry:
+	if (opcodes - orig_opcodes > MAX_INSN_SIZE) return 0;
+	opcode = *(opcodes++);
+	/* 2nd-byte opcode */
+	if (opcode == 0x0f)
+		return boostable_2nd_opcode[*opcodes];
+	
+	switch (opcode & 0xf0) {
+	case 0x60:
+		if (0x63 < opcode && opcode < 0x67)
+			goto retry; /* prefixes */
+		/* can't boost Address-size override and bound */
+		return (opcode != 0x62 && opcode != 0x67);
 	case 0x70:
 		return 0; /* can't boost conditional jump */
-	case 0x90:
-		/* can't boost call and pushf */
-		return opcode != 0x9a && opcode != 0x9c;
 	case 0xc0:
-		/* can't boost undefined opcodes and soft-interruptions */
-		return (0xc1 < opcode && opcode < 0xc6) ||
-			(0xc7 < opcode && opcode < 0xcc) || opcode == 0xcf;
+		/* can't boost software-interruptions */
+		return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
 	case 0xd0:
 		/* can boost AA* and XLAT */
 		return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
 	case 0xe0:
-		/* can boost in/out and (may be) jmps */
-		return (0xe3 < opcode && opcode != 0xe8);
+		/* can boost in/out and absolute jmps */
+		return ((opcode & 0x04) || opcode == 0xea);
 	case 0xf0:
+		if ((opcode & 0x0c) == 0 && opcode != 0xf1)
+			goto retry; /* lock/rep(ne) prefix */
 		/* clear and set flags can be boost */
 		return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
 	default:
-		/* currently, can't boost 2 bytes opcodes */
-		return opcode != 0x0f;
+		if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
+			goto retry; /* prefixes */
+		/* can't boost CS override and call */
+		return (opcode != 0x2e && opcode != 0x9a);
 	}
 }

@@ -109,7 +146,7 @@ int __kprobes arch_prepare_kprobe(struct

 	memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 	p->opcode = *p->addr;
-	if (can_boost(p->opcode)) {
+	if (can_boost(p->addr)) {
 		p->ainsn.boostable = 0;
 	} else {
 		p->ainsn.boostable = -1;



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