Subject: [PATCH v3 1/7] arm64: introduce basic aarch64 instruction decoding helpers

From: [email-masked] (Jiang Liu)
Date: Thu, 17 Oct 2013 01:14:50 +0800

On 10/16/2013 11:36 PM, Jiang Liu wrote:
> On 10/16/2013 06:51 PM, Will Deacon wrote:
>> On Wed, Oct 16, 2013 at 04:18:06AM +0100, Jiang Liu wrote:
>>> From: Jiang Liu <[email-masked]>
>>>
>>> Introduce basic aarch64 instruction decoding helper
>>> aarch64_get_insn_class() and aarch64_insn_hotpatch_safe().
>>>
>>> Signed-off-by: Jiang Liu <[email-masked]>
>>> Cc: Jiang Liu <[email-masked]>
>>> ---
>>>  arch/arm64/include/asm/insn.h | 53 ++++++++++++++++++++++++++
>>>  arch/arm64/kernel/Makefile    |  2 +-
>>>  arch/arm64/kernel/insn.c      | 86 +++++++++++++++++++++++++++++++++++++++++++
>>>  3 files changed, 140 insertions(+), 1 deletion(-)
>>>  create mode 100644 arch/arm64/include/asm/insn.h
>>>  create mode 100644 arch/arm64/kernel/insn.c
>>>
>>> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
>>> new file mode 100644
>>> index 0000000..e7d1bc8
>>> --- /dev/null
>>> +++ b/arch/arm64/include/asm/insn.h
>>> @@ -0,0 +1,53 @@
>>> +/*
>>> + * Copyright (C) 2013 Huawei Ltd.
>>> + * Author: Jiang Liu <[email-masked]>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License version 2 as
>>> + * published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License
>>> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>> + */
>>> +#ifndef	_ASM_ARM64_INSN_H
>>> +#define	_ASM_ARM64_INSN_H
>>> +#include <linux/types.h>
>>> +
>>> +enum aarch64_insn_class {
>>> +	AARCH64_INSN_CLS_UNKNOWN,	/* UNALLOCATED */
>>> +	AARCH64_INSN_CLS_DP_IMM,	/* Data processing - immediate */
>>> +	AARCH64_INSN_CLS_DP_REG,	/* Data processing - register */
>>> +	AARCH64_INSN_CLS_DP_FPSIMD,	/* Data processing - SIMD and FP */
>>> +	AARCH64_INSN_CLS_LDST,		/* Loads and stores */
>>> +	AARCH64_INSN_CLS_BR_SYS,	/* Branch, exception generation and
>>> +					 * system instructions */
>>> +};
>>
>> Strictly speaking, these are encoding groups, not instruction classes.
> Hi Will,
> 	Thanks for review.
> Will change it to "aarch64_insn_encoding_class.
> 
>>
>>> +
>>> +#define	__AARCH64_INSN_FUNCS(abbr, mask, val)	\
>>> +static __always_inline bool aarch64_insn_is_##abbr(u32 code) \
>>> +{ return (code & (mask)) == (val); }	\
>>> +static __always_inline u32 aarch64_insn_get_##abbr##_mask(void) \
>>> +{ return (mask); } \
>>> +static __always_inline u32 aarch64_insn_get_##abbr##_value(void) \
>>> +{ return (val); }
>>> +
>>> +__AARCH64_INSN_FUNCS(b,		0xFC000000, 0x14000000)
>>> +__AARCH64_INSN_FUNCS(bl,	0xFC000000, 0x94000000)
>>> +__AARCH64_INSN_FUNCS(svc,	0xFFE0001F, 0xD4000001)
>>> +__AARCH64_INSN_FUNCS(hvc,	0xFFE0001F, 0xD4000002)
>>> +__AARCH64_INSN_FUNCS(smc,	0xFFE0001F, 0xD4000003)
>>> +__AARCH64_INSN_FUNCS(brk,	0xFFE0001F, 0xD4200000)
>>> +__AARCH64_INSN_FUNCS(nop,	0xFFFFFFFF, 0xD503201F)
>>> +
>>> +#undef	__AARCH64_INSN_FUNCS
>>> +
>>> +enum aarch64_insn_class aarch64_get_insn_class(u32 insn);
>>> +
>>> +bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);
>>> +
>>> +#endif	/* _ASM_ARM64_INSN_H */
>>> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
>>> index 7b4b564..9af6cb3 100644
>>> --- a/arch/arm64/kernel/Makefile
>>> +++ b/arch/arm64/kernel/Makefile
>>> @@ -9,7 +9,7 @@ AFLAGS_head.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)
>>>  arm64-obj-y		:= cputable.o debug-monitors.o entry.o irq.o fpsimd.o	\
>>>  			   entry-fpsimd.o process.o ptrace.o setup.o signal.o	\
>>>  			   sys.o stacktrace.o time.o traps.o io.o vdso.o	\
>>> -			   hyp-stub.o psci.o
>>> +			   hyp-stub.o psci.o insn.o
>>>  
>>>  arm64-obj-$(CONFIG_COMPAT)		+= sys32.o kuser32.o signal32.o 	\
>>>  					   sys_compat.o
>>> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
>>> new file mode 100644
>>> index 0000000..1be4d11
>>> --- /dev/null
>>> +++ b/arch/arm64/kernel/insn.c
>>> @@ -0,0 +1,86 @@
>>> +/*
>>> + * Copyright (C) 2013 Huawei Ltd.
>>> + * Author: Jiang Liu <[email-masked]>
>>> + *
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License version 2 as
>>> + * published by the Free Software Foundation.
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + *
>>> + * You should have received a copy of the GNU General Public License
>>> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>> + */
>>> +#include <linux/compiler.h>
>>> +#include <linux/kernel.h>
>>> +#include <asm/insn.h>
>>> +
>>> +/*
>>> + * ARM Architecture Reference Manual ARMv8, Section C3.1
>>> + * AARCH64 main encoding table
>>
>> AArch64.
> Fix it in next version.
> 
>>
>>> + *  Bit position
>>> + *   28 27 26 25	Encoding Group
>>> + *   0  0  -  -		Unallocated
>>> + *   1  0  0  -		Data processing, immediate
>>> + *   1  0  1  -		Branch, exception generation and system instructions
>>> + *   -  1  -  0		Loads and stores
>>> + *   -  1  0  1		Data processing - register
>>> + *   0  1  1  1		Data processing - SIMD and floating point
>>> + *   1  1  1  1		Data processing - SIMD and floating point
>>> + * "-" means "don't care"
>>> + */
>>
>> This comment would probably be better off in the header file, along with the
>> mask/value pairs you use there. Failing that, the table below should at
>> least live alongside the enum type and mask/value stuff.
> Will move it into insn.h
> 
>>
>>> +static int aarch64_insn_cls[] = {
>>> +	AARCH64_INSN_CLS_UNKNOWN,
>>> +	AARCH64_INSN_CLS_UNKNOWN,
>>> +	AARCH64_INSN_CLS_UNKNOWN,
>>> +	AARCH64_INSN_CLS_UNKNOWN,
>>> +	AARCH64_INSN_CLS_LDST,
>>> +	AARCH64_INSN_CLS_DP_REG,
>>> +	AARCH64_INSN_CLS_LDST,
>>> +	AARCH64_INSN_CLS_DP_FPSIMD,
>>> +	AARCH64_INSN_CLS_DP_IMM,
>>> +	AARCH64_INSN_CLS_DP_IMM,
>>> +	AARCH64_INSN_CLS_BR_SYS,
>>> +	AARCH64_INSN_CLS_BR_SYS,
>>> +	AARCH64_INSN_CLS_LDST,
>>> +	AARCH64_INSN_CLS_DP_REG,
>>> +	AARCH64_INSN_CLS_LDST,
>>> +	AARCH64_INSN_CLS_DP_FPSIMD,
>>> +};
>>> +
>>> +enum aarch64_insn_class __kprobes aarch64_get_insn_class(u32 insn)
>>> +{
>>> +	return aarch64_insn_cls[(insn >> 25) & 0xf];
>>> +}
>>> +
>>> +static bool __kprobes __aarch64_insn_hotpatch_safe(u32 insn)
>>> +{
>>> +	if (aarch64_get_insn_class(insn) != AARCH64_INSN_CLS_BR_SYS)
>>> +		return false;
>>> +
>>> +	return	aarch64_insn_is_b(insn) ||
>>> +		aarch64_insn_is_bl(insn) ||
>>> +		aarch64_insn_is_svc(insn) ||
>>> +		aarch64_insn_is_hvc(insn) ||
>>> +		aarch64_insn_is_smc(insn) ||
>>> +		aarch64_insn_is_brk(insn) ||
>>> +		aarch64_insn_is_nop(insn);
>>> +}
>>> +
>>> +/*
>>> + * ARMv8-A Section B2.6.5:
>>> + * Concurrent modification and execution of instructions can lead to the
>>> + * resulting instruction performing any behavior that can be achieved by
>>> + * executing any sequence of instructions that can be executed from the
>>> + * same Exception level, except where the instruction before modification
>>> + * and the instruction after modification is a B, BL, NOP, BKPT, SVC, HVC,
>>> + * or SMC instruction.
>>> + */
>>> +bool __kprobes aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn)
>>> +{
>>> +	return __aarch64_insn_hotpatch_safe(old_insn) &&
>>> +	       __aarch64_insn_hotpatch_safe(new_insn);
>>
>> Take care here:
>>
>> 	- This doesn't guarantee that CPUs exclusively see new_insn (they
>> 	  may see old_insn, even after patching)
> Good point. Still need some synchronization mechanism lighter than
> stop_machine(). How about kick_all_cpus_sync(), which should be lighter
> than stop_machine()?
For jump label, x86 uses three smp_call_function() to replace a
stop_machine(). Seems it's valuable for us to use just one
kick_all_cpus_sync() to avoid a stop_machine().

Thanks!
Gerry

> 
>>
>> 	- If you patch a conditional branch and change both the target address
>> 	  *and* the condition, you can get combinations of target/condition
>> 	  between old_insn and new_insn.
>>
>> Then again, the jump_label code should always be patching between B and NOP
>> instructions, right?
> Yeah, should be safe for jump label because it only uses unconditional
> B and NOP.
> 
>>
>> Will
>>
>