linux-kernel - Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use extable type EX_TYPE_UACCESS_ERR

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Message-ID: <4371a7c9-8766-9fee-2558-e6f43f06ad19@huawei.com>
Date:   Sat, 18 Jun 2022 11:26:30 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     James Morse <james.morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Robin Murphy <robin.murphy@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Catalin Marinas" <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Alexander Viro" <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Xie XiuQi <xiexiuqi@...wei.com>,
        Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use
 extable type EX_TYPE_UACCESS_ERR_ZERO



在 2022/6/17 16:24, Mark Rutland 写道:
> On Sat, May 28, 2022 at 06:50:50AM +0000, Tong Tiangen wrote:
>> Currnetly, the extable type used by __arch_copy_from/to_user() is
>> EX_TYPE_FIXUP. In fact, It is more clearly to use meaningful
>> EX_TYPE_UACCESS_*.
>>
>> Suggested-by: Mark Rutland <mark.rutland@....com>
>> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
>> ---
>>   arch/arm64/include/asm/asm-extable.h |  8 ++++++++
>>   arch/arm64/include/asm/asm-uaccess.h | 12 ++++++------
>>   2 files changed, 14 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
>> index 56ebe183e78b..9c94ac1f082c 100644
>> --- a/arch/arm64/include/asm/asm-extable.h
>> +++ b/arch/arm64/include/asm/asm-extable.h
>> @@ -28,6 +28,14 @@
>>   	__ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
>>   	.endm
>>   
>> +/*
>> + * Create an exception table entry for uaccess `insn`, which will branch to `fixup`
>> + * when an unhandled fault is taken.
>> + * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
>> + */
>> +	.macro          _asm_extable_uaccess, insn, fixup
>> +	__ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
>> +	.endm
> 
> I'm not too keen on using `~0` here, since that also sets other bits in the
> data field, and its somewhat opaque.
> 
> How painful is it to generate the data fields as with the C version of this
> macro, so that we can pass in wzr explciitly for the two sub-fields?
> 
> Other than that, this looks good to me.
> 
> Thanks,
> Mark.

ok, will fix next version.

Thanks,
Tong.

> 
>>   /*
>>    * Create an exception table entry for `insn` if `fixup` is provided. Otherwise
>>    * do nothing.
>> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
>> index 0557af834e03..75b211c98dea 100644
>> --- a/arch/arm64/include/asm/asm-uaccess.h
>> +++ b/arch/arm64/include/asm/asm-uaccess.h
>> @@ -61,7 +61,7 @@ alternative_else_nop_endif
>>   
>>   #define USER(l, x...)				\
>>   9999:	x;					\
>> -	_asm_extable	9999b, l
>> +	_asm_extable_uaccess	9999b, l
>>   
>>   /*
>>    * Generate the assembly for LDTR/STTR with exception table entries.
>> @@ -73,8 +73,8 @@ alternative_else_nop_endif
>>   8889:		ldtr	\reg2, [\addr, #8];
>>   		add	\addr, \addr, \post_inc;
>>   
>> -		_asm_extable	8888b,\l;
>> -		_asm_extable	8889b,\l;
>> +		_asm_extable_uaccess	8888b, \l;
>> +		_asm_extable_uaccess	8889b, \l;
>>   	.endm
>>   
>>   	.macro user_stp l, reg1, reg2, addr, post_inc
>> @@ -82,14 +82,14 @@ alternative_else_nop_endif
>>   8889:		sttr	\reg2, [\addr, #8];
>>   		add	\addr, \addr, \post_inc;
>>   
>> -		_asm_extable	8888b,\l;
>> -		_asm_extable	8889b,\l;
>> +		_asm_extable_uaccess	8888b,\l;
>> +		_asm_extable_uaccess	8889b,\l;
>>   	.endm
>>   
>>   	.macro user_ldst l, inst, reg, addr, post_inc
>>   8888:		\inst		\reg, [\addr];
>>   		add		\addr, \addr, \post_inc;
>>   
>> -		_asm_extable	8888b,\l;
>> +		_asm_extable_uaccess	8888b, \l;
>>   	.endm
>>   #endif
>> -- 
>> 2.25.1
>>
> .