linux-kernel - Re: [RFC PATCH -next V2 4/7] arm64: add copy_from_user to machine check safe

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Date:   Thu, 7 Apr 2022 22:28:02 +0800
From:   Tong Tiangen <tongtiangen@...wei.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [RFC PATCH -next V2 4/7] arm64: add copy_from_user to machine
 check safe

在 2022/4/6 19:19, Mark Rutland 写道:
> On Wed, Apr 06, 2022 at 09:13:08AM +0000, Tong Tiangen wrote:
>> Add scenarios copy_from_user to machine check safe.
>>
>> The data copied is user data and is machine check safe, so just kill
>> the user process and isolate the error page, not necessary panic.
>>
>> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
>> ---
>>   arch/arm64/include/asm/asm-uaccess.h | 16 ++++++++++++++++
>>   arch/arm64/lib/copy_from_user.S      | 11 ++++++-----
>>   2 files changed, 22 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
>> index 0557af834e03..f31c8978e1af 100644
>> --- a/arch/arm64/include/asm/asm-uaccess.h
>> +++ b/arch/arm64/include/asm/asm-uaccess.h
>> @@ -92,4 +92,20 @@ alternative_else_nop_endif
>>   
>>   		_asm_extable	8888b,\l;
>>   	.endm
>> +
>> +	.macro user_ldp_mc l, reg1, reg2, addr, post_inc
>> +8888:		ldtr	\reg1, [\addr];
>> +8889:		ldtr	\reg2, [\addr, #8];
>> +		add	\addr, \addr, \post_inc;
>> +
>> +		_asm_extable_mc	8888b, \l;
>> +		_asm_extable_mc	8889b, \l;
>> +	.endm
>> +
>> +	.macro user_ldst_mc l, inst, reg, addr, post_inc
>> +8888:		\inst		\reg, [\addr];
>> +		add		\addr, \addr, \post_inc;
>> +
>> +		_asm_extable_mc	8888b, \l;
>> +	.endm
>>   #endif
>> diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
>> index 34e317907524..d9d7c5291871 100644
>> --- a/arch/arm64/lib/copy_from_user.S
>> +++ b/arch/arm64/lib/copy_from_user.S
>> @@ -21,7 +21,7 @@
>>    */
>>   
>>   	.macro ldrb1 reg, ptr, val
>> -	user_ldst 9998f, ldtrb, \reg, \ptr, \val
>> +	user_ldst_mc 9998f, ldtrb, \reg, \ptr, \val
>>   	.endm
>>   
>>   	.macro strb1 reg, ptr, val
>> @@ -29,7 +29,7 @@
>>   	.endm
>>   
>>   	.macro ldrh1 reg, ptr, val
>> -	user_ldst 9997f, ldtrh, \reg, \ptr, \val
>> +	user_ldst_mc 9997f, ldtrh, \reg, \ptr, \val
>>   	.endm
>>   
>>   	.macro strh1 reg, ptr, val
>> @@ -37,7 +37,7 @@
>>   	.endm
>>   
>>   	.macro ldr1 reg, ptr, val
>> -	user_ldst 9997f, ldtr, \reg, \ptr, \val
>> +	user_ldst_mc 9997f, ldtr, \reg, \ptr, \val
>>   	.endm
>>   
>>   	.macro str1 reg, ptr, val
>> @@ -45,7 +45,7 @@
>>   	.endm
>>   
>>   	.macro ldp1 reg1, reg2, ptr, val
>> -	user_ldp 9997f, \reg1, \reg2, \ptr, \val
>> +	user_ldp_mc 9997f, \reg1, \reg2, \ptr, \val
>>   	.endm
>>   
>>   	.macro stp1 reg1, reg2, ptr, val
>> @@ -62,7 +62,8 @@ SYM_FUNC_START(__arch_copy_from_user)
>>   	ret
>>   
>>   	// Exception fixups
>> -9997:	cmp	dst, dstin
>> +9997:	cbz	x0, 9998f			// Check machine check exception
>> +	cmp	dst, dstin
>>   	b.ne	9998f
> 
> If you look at the copy template, you'd see that `dstin` *is* x0.
> 
> Consier if we took a non-SEA fault. The the fixup handler will overwrite x0,
> it's likely `dst` != `dstin`, and we'll branch to the byte-by-byte copy. Or if
> we're doing something odd and mmap_min_addr is 0, we can do the wrong thing the
> other way around and *not* branch to the byte-by-byte copy when we should.
> 
> So this is at best confusing, but likely broken too.
> 
> Thanks,
> Mark.

OK, missing that, will be fixed in next verison.

Thanks,
Tong.

> 
>>   	// Before being absolutely sure we couldn't copy anything, try harder
>>   USER(9998f, ldtrb tmp1w, [srcin])
>> -- 
>> 2.18.0.huawei.25
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> .

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