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SubjectRe: [RFC PATCH -next V2 4/7] arm64: add copy_from_user to machine check safe
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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@huawei.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@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> .

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