Subject: [PATCH] ARM: kprobes: check register usage for probed instruction

From: [email-masked] (Wang Nan)
Date: Mon, 19 Jan 2015 18:37:00 +0800

I think this patch is better than mo original one.

Thanks to Tixy.

On 2015/1/14 0:13, Jon Medhurst (Tixy) wrote:
> This patch utilizes the previously introduced checker to check
> register usage for probed ARM instruction and saves it in a mask.
> A further patch will use such information to avoid simulation or
> emulation.
> 
> Signed-off-by: Wang Nan <[email-masked]>
> Reviewed-by: Jon Medhurst <[email-masked]>
> Signed-off-by: Jon Medhurst <[email-masked]>
> ---
> 
> This patch applies my review comments on "[PATCH v19 10/11] ARM:
> kprobes: check register usage for probed instruction."
> 
> It is also rebased on top of the kprobes-opt branch at
> git://git.linaro.org/people/tixy/kernel.git
> 
>  arch/arm/include/asm/probes.h          |  1 +
>  arch/arm/probes/decode.c               |  7 +++
>  arch/arm/probes/kprobes/actions-arm.c  |  2 +-
>  arch/arm/probes/kprobes/checkers-arm.c | 93 ++++++++++++++++++++++++++++++++++
>  arch/arm/probes/kprobes/checkers.h     |  1 +
>  5 files changed, 103 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/probes.h b/arch/arm/include/asm/probes.h
> index cd9e815..b668e60 100644
> --- a/arch/arm/include/asm/probes.h
> +++ b/arch/arm/include/asm/probes.h
> @@ -41,6 +41,7 @@ struct arch_probes_insn {
>  	probes_insn_singlestep_t	*insn_singlestep;
>  	probes_insn_fn_t		*insn_fn;
>  	int				stack_space;
> +	unsigned long			register_usage_flags;
>  };
>  
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/arm/probes/decode.c b/arch/arm/probes/decode.c
> index f9d7c42..880ebe0 100644
> --- a/arch/arm/probes/decode.c
> +++ b/arch/arm/probes/decode.c
> @@ -435,6 +435,13 @@ probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
>  	 */
>  	asi->stack_space = 0;
>  
> +	/*
> +	 * Similarly to stack_space, register_usage_flags is filled by
> +	 * checkers. Its default value is set to ~0, which is 'all
> +	 * registers are used', to prevent any potential optimization.
> +	 */
> +	asi->register_usage_flags = ~0UL;
> +
>  	if (emulate)
>  		insn = prepare_emulated_insn(insn, asi, thumb);
>  
> diff --git a/arch/arm/probes/kprobes/actions-arm.c b/arch/arm/probes/kprobes/actions-arm.c
> index 06988ef..b9056d6 100644
> --- a/arch/arm/probes/kprobes/actions-arm.c
> +++ b/arch/arm/probes/kprobes/actions-arm.c
> @@ -341,4 +341,4 @@ const union decode_action kprobes_arm_actions[NUM_PROBES_ARM_ACTIONS] = {
>  	[PROBES_LDMSTM] = {.decoder = kprobe_decode_ldmstm}
>  };
>  
> -const struct decode_checker *kprobes_arm_checkers[] = {arm_stack_checker, NULL};
> +const struct decode_checker *kprobes_arm_checkers[] = {arm_stack_checker, arm_regs_checker, NULL};
> diff --git a/arch/arm/probes/kprobes/checkers-arm.c b/arch/arm/probes/kprobes/checkers-arm.c
> index f817663..7b98173 100644
> --- a/arch/arm/probes/kprobes/checkers-arm.c
> +++ b/arch/arm/probes/kprobes/checkers-arm.c
> @@ -97,3 +97,96 @@ const struct decode_checker arm_stack_checker[NUM_PROBES_ARM_ACTIONS] = {
>  	[PROBES_STORE] = {.checker = arm_check_stack},
>  	[PROBES_LDMSTM] = {.checker = arm_check_stack},
>  };
> +
> +static enum probes_insn __kprobes arm_check_regs_nouse(probes_opcode_t insn,
> +		struct arch_probes_insn *asi,
> +		const struct decode_header *h)
> +{
> +	asi->register_usage_flags = 0;
> +	return INSN_GOOD;
> +}
> +
> +static enum probes_insn arm_check_regs_normal(probes_opcode_t insn,
> +		struct arch_probes_insn *asi,
> +		const struct decode_header *h)
> +{
> +	u32 regs = h->type_regs.bits >> DECODE_TYPE_BITS;
> +	int i;
> +
> +	asi->register_usage_flags = 0;
> +	for (i = 0; i < 5; regs >>= 4, insn >>= 4, i++)
> +		if (regs & 0xf)
> +			asi->register_usage_flags |= 1 << (insn & 0xf);
> +
> +	return INSN_GOOD;
> +}
> +
> +
> +static enum probes_insn arm_check_regs_ldmstm(probes_opcode_t insn,
> +		struct arch_probes_insn *asi,
> +		const struct decode_header *h)
> +{
> +	unsigned int reglist = insn & 0xffff;
> +	unsigned int rn = (insn >> 16) & 0xf;
> +	asi->register_usage_flags = reglist | (1 << rn);
> +	return INSN_GOOD;
> +}
> +
> +static enum probes_insn arm_check_regs_mov_ip_sp(probes_opcode_t insn,
> +		struct arch_probes_insn *asi,
> +		const struct decode_header *h)
> +{
> +	/* Instruction is 'mov ip, sp' i.e. 'mov r12, r13' */
> +	asi->register_usage_flags = (1 << 12) | (1<< 13);
> +	return INSN_GOOD;
> +}
> +
> +/*
> + *                                    | Rn |Rt/d|         | Rm |
> + * LDRD (register)      cccc 000x x0x0 xxxx xxxx xxxx 1101 xxxx
> + * STRD (register)      cccc 000x x0x0 xxxx xxxx xxxx 1111 xxxx
> + *                                    | Rn |Rt/d|         |imm4L|
> + * LDRD (immediate)     cccc 000x x1x0 xxxx xxxx xxxx 1101 xxxx
> + * STRD (immediate)     cccc 000x x1x0 xxxx xxxx xxxx 1111 xxxx
> + *
> + * Such instructions access Rt/d and its next register, so different
> + * from others, a specific checker is required to handle this extra
> + * implicit register usage.
> + */
> +static enum probes_insn arm_check_regs_ldrdstrd(probes_opcode_t insn,
> +		struct arch_probes_insn *asi,
> +		const struct decode_header *h)
> +{
> +	int rdt = (insn >> 12) & 0xf;
> +	arm_check_regs_normal(insn, asi, h);
> +	asi->register_usage_flags |= 1 << (rdt + 1);
> +	return INSN_GOOD;
> +}
> +
> +
> +const struct decode_checker arm_regs_checker[NUM_PROBES_ARM_ACTIONS] = {
> +	[PROBES_MRS] = {.checker = arm_check_regs_normal},
> +	[PROBES_SATURATING_ARITHMETIC] = {.checker = arm_check_regs_normal},
> +	[PROBES_MUL1] = {.checker = arm_check_regs_normal},
> +	[PROBES_MUL2] = {.checker = arm_check_regs_normal},
> +	[PROBES_MUL_ADD_LONG] = {.checker = arm_check_regs_normal},
> +	[PROBES_MUL_ADD] = {.checker = arm_check_regs_normal},
> +	[PROBES_LOAD] = {.checker = arm_check_regs_normal},
> +	[PROBES_LOAD_EXTRA] = {.checker = arm_check_regs_normal},
> +	[PROBES_STORE] = {.checker = arm_check_regs_normal},
> +	[PROBES_STORE_EXTRA] = {.checker = arm_check_regs_normal},
> +	[PROBES_DATA_PROCESSING_REG] = {.checker = arm_check_regs_normal},
> +	[PROBES_DATA_PROCESSING_IMM] = {.checker = arm_check_regs_normal},
> +	[PROBES_SEV] = {.checker = arm_check_regs_nouse},
> +	[PROBES_WFE] = {.checker = arm_check_regs_nouse},
> +	[PROBES_SATURATE] = {.checker = arm_check_regs_normal},
> +	[PROBES_REV] = {.checker = arm_check_regs_normal},
> +	[PROBES_MMI] = {.checker = arm_check_regs_normal},
> +	[PROBES_PACK] = {.checker = arm_check_regs_normal},
> +	[PROBES_EXTEND] = {.checker = arm_check_regs_normal},
> +	[PROBES_EXTEND_ADD] = {.checker = arm_check_regs_normal},
> +	[PROBES_BITFIELD] = {.checker = arm_check_regs_normal},
> +	[PROBES_LDMSTM] = {.checker = arm_check_regs_ldmstm},
> +	[PROBES_MOV_IP_SP] = {.checker = arm_check_regs_mov_ip_sp},
> +	[PROBES_LDRSTRD] = {.checker = arm_check_regs_ldrdstrd},
> +};
> diff --git a/arch/arm/probes/kprobes/checkers.h b/arch/arm/probes/kprobes/checkers.h
> index bddfa0e..cf6c9e7 100644
> --- a/arch/arm/probes/kprobes/checkers.h
> +++ b/arch/arm/probes/kprobes/checkers.h
> @@ -47,6 +47,7 @@ extern const union decode_action stack_check_actions[];
>  
>  #ifndef CONFIG_THUMB2_KERNEL
>  extern const struct decode_checker arm_stack_checker[];
> +extern const struct decode_checker arm_regs_checker[];
>  #else
>  #endif
>  extern const struct decode_checker t32_stack_checker[];
>