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

From: [email-masked] (Jiang Liu)
Date: Wed, 16 Oct 2013 23:36:25 +0800

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()?

> 
> 	- 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