Subject: [PATCH 1/4] ARM: kprobes: fix instruction fetch order with <asm/opcodes.h>

From: [email-masked] (Ben Dooks)
Date: Wed, 31 Jul 2013 20:43:07 +0100

On 29/07/13 09:01, Jon Medhurst (Tixy) wrote:
> On Thu, 2013-07-25 at 22:08 +0100, Ben Dooks wrote:
>> If we are running BE8, the data and instruction endian-ness do not
>> match, so use<asm/opcodes.h>  to correctly translate memory accesses
>> into ARM instructions.
>>
>> Signed-off-by: Ben Dooks<[email-masked]>y
>> ---
>>   arch/arm/kernel/kprobes-common.c |   14 ++++++++------
>>   arch/arm/kernel/kprobes.c        |    9 +++++----
>>   2 files changed, 13 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/arm/kernel/kprobes-common.c b/arch/arm/kernel/kprobes-common.c
>> index 18a7628..c0b202e 100644
>> --- a/arch/arm/kernel/kprobes-common.c
>> +++ b/arch/arm/kernel/kprobes-common.c
>> @@ -14,6 +14,7 @@
>>   #include<linux/kernel.h>
>>   #include<linux/kprobes.h>
>>   #include<asm/system_info.h>
>> +#include<asm/opcodes.h>
>>
>>   #include "kprobes.h"
>>
>> @@ -305,7 +306,8 @@ kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_specific_insn *asi)
>>
>>   	if (handler) {
>>   		/* We can emulate the instruction in (possibly) modified form */
>> -		asi->insn[0] = (insn&  0xfff00000) | (rn<<  16) | reglist;
>> +		asi->insn[0] = __opcode_to_mem_arm((insn&  0xfff00000) |
>> +						   (rn<<  16) | reglist);
>>   		asi->insn_handler = handler;
>>   		return INSN_GOOD;
>>   	}
>> @@ -338,9 +340,9 @@ prepare_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
>>   		thumb_insn[2] = 0x4770; /* Thumb bx lr */
>
> The line above and the one before it not in this diff also need fixing
> by changing to __opcode_to_mem_thumb16(0x4770).

IIRC, these are then fixed by the set_emulated instruction, which is
also why the insn return is not swapped.

>>   		return insn;
>>   	}
>> -	asi->insn[1] = 0xe12fff1e; /* ARM bx lr */
>> +	asi->insn[1] = __opcode_to_mem_arm(0xe12fff1e); /* ARM bx lr */
>>   #else
>> -	asi->insn[1] = 0xe1a0f00e; /* mov pc, lr */
>> +	asi->insn[1] = __opcode_to_mem_arm(0xe1a0f00e); /* mov pc, lr */
>>   #endif
>>   	/* Make an ARM instruction unconditional */
>>   	if (insn<  0xe0000000)
>> @@ -360,12 +362,12 @@ set_emulated_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi,
>>   	if (thumb) {
>>   		u16 *ip = (u16 *)asi->insn;
>>   		if (is_wide_instruction(insn))
>> -			*ip++ = insn>>  16;
>> -		*ip++ = insn;
>> +			*ip++ = ___asm_opcode_to_mem_thumb16(insn>>  16);
>> +		*ip++ = ___asm_opcode_to_mem_thumb16(insn);
>
>
> Should these two ___asm_opcode_thumb32_compose() not be
> __opcode_thumb32_compose() ?

I decided to leave this as is.

>>   		return;
>>   	}
>>   #endif
>> -	asi->insn[0] = insn;
>> +	asi->insn[0] = __opcode_to_mem_arm(insn);
>>   }
>>
>>   /*
>> diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c
>> index 170e9f3..3775af1 100644
>> --- a/arch/arm/kernel/kprobes.c
>> +++ b/arch/arm/kernel/kprobes.c
>> @@ -26,6 +26,7 @@
>>   #include<linux/stop_machine.h>
>>   #include<linux/stringify.h>
>>   #include<asm/traps.h>
>> +#include<asm/opcodes.h>
>>   #include<asm/cacheflush.h>
>>
>>   #include "kprobes.h"
>> @@ -62,10 +63,10 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>>   #ifdef CONFIG_THUMB2_KERNEL
>>   	thumb = true;
>>   	addr&= ~1; /* Bit 0 would normally be set to indicate Thumb code */
>> -	insn = ((u16 *)addr)[0];
>> +	insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
>>   	if (is_wide_instruction(insn)) {
>> -		insn<<= 16;
>> -		insn |= ((u16 *)addr)[1];
>> +		u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
>> +		insn = ___asm_opcode_thumb32_compose(insn, inst2);
>
> Again, __opcode_thumb32_compose instead of
> ___asm_opcode_thumb32_compose
>
>>   		decode_insn = thumb32_kprobe_decode_insn;
>>   	} else
>>   		decode_insn = thumb16_kprobe_decode_insn;
>> @@ -73,7 +74,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
>>   	thumb = false;
>>   	if (addr&  0x3)
>>   		return -EINVAL;
>> -	insn = *p->addr;
>> +	insn = __mem_to_opcode_arm(*p->addr);
>>   	decode_insn = arm_kprobe_decode_insn;
>>   #endif
>>
>

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius