Re: [PATCH] kprobe: kprobe-2byte-booster

[Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>]

On Wed, Apr 12, 2006 at 07:10:30PM +0900, Masami Hiramatsu wrote:
> 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.

Masami,

Few comments below (I am not too well versed with IA32 internals to
comment on the intricacies).

Ananth

> 
> 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
> +};

Please fix codingstyle per what Roland's rip-relative instruction
support code in arch/x86_64/kernel/kprobes.c

> +
> +/*
>   * 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;

CodingStyle

> +	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;
>