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Subject[PATCH] kprobe: boost 2byte-opcodes on i386
Hi, Andrew

Here is a patch of kprobe-booster enhancement on i386
This patch can be applied against 2.6.17-rc2.

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

Signed-off-by: Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp>

kprobes.c | 78 +++++++++++++++++++++++++++++++++++++++++++++++++++-----------
1 files changed, 65 insertions(+), 13 deletions(-)
diff -Narup a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
--- a/arch/i386/kernel/kprobes.c 2006-04-21 12:23:45.000000000 +0900
+++ b/arch/i386/kernel/kprobes.c 2006-04-21 21:27:08.000000000 +0900
@@ -57,30 +57,82 @@ static inline void set_jmp_op(void *from
/*
* 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 ) {
+#define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf) \
+ (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) | \
+ (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) | \
+ (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) | \
+ (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf)) \
+ << (row % 32))
+ /*
+ * Undefined/reserved opcodes, conditional jump, Opcode Extension
+ * Groups, and some special opcodes can not be boost.
+ */
+ static const unsigned long twobyte_is_boostable[256 / 32] = {
+ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
+ /* ------------------------------- */
+ W(0x00, 0,0,1,1,0,0,1,0,1,1,0,0,0,0,0,0)| /* 00 */
+ W(0x10, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 10 */
+ W(0x20, 1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0)| /* 20 */
+ W(0x30, 0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 30 */
+ W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 40 */
+ W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 50 */
+ W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,0,0,1,1)| /* 60 */
+ W(0x70, 0,0,0,0,1,1,1,1,0,0,0,0,0,0,1,1), /* 70 */
+ W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 80 */
+ W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1), /* 90 */
+ W(0xa0, 1,1,0,1,1,1,0,0,1,1,0,1,1,1,0,1)| /* a0 */
+ W(0xb0, 1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1), /* b0 */
+ W(0xc0, 1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1)| /* c0 */
+ W(0xd0, 0,1,1,1,0,1,0,0,1,1,0,1,1,1,0,1), /* d0 */
+ W(0xe0, 0,1,1,0,0,1,0,0,1,1,0,1,1,1,0,1)| /* e0 */
+ W(0xf0, 0,1,1,1,0,1,0,0,1,1,1,0,1,1,1,0) /* f0 */
+ /* ------------------------------- */
+ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
+ };
+#undef W
+ kprobe_opcode_t opcode;
+ kprobe_opcode_t *orig_opcodes = opcodes;
+retry:
+ if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
+ return 0;
+ opcode = *(opcodes++);
+
+ /* 2nd-byte opcode */
+ if (opcode == 0x0f) {
+ if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
+ return 0;
+ return test_bit(*opcodes, twobyte_is_boostable);
+ }
+
+ 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 +161,7 @@ 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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