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

[Ben Dooks]

On 02/08/13 14:57, Dave Martin wrote:
> On Wed, Jul 31, 2013 at 08:43:07PM +0100, Ben Dooks wrote:
>> 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<ben.dooks at codethink.co.uk>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.
>
> Although the intent is not made as clear in the header as it could be,
> the ___asm() functions are not supposed to be used directly:
> __opcode_thumb32_compose() will map to the correct thing based on
> whether we are preprocessing assembler or C.
>
> In particular, ___asm_opcode_thumb32_compose() will give you inefficient
> swabbing if used directly in C.
>
>>>>   		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
>
> ditto, this should be changed.
>
> Cheers
> ---Dave

Yes, already fixed thanks.

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