linux-kernel - Re: [PATCH -next] riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit

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Date:   Fri, 15 Jul 2022 11:47:01 +0800
From:   chenlifu <chenlifu@...wei.com>
To:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <akira.tsukamoto@...il.com>,
        <jszhang@...nel.org>, <wangkefeng.wang@...wei.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <alankao@...estech.com>
Subject: Re: [PATCH -next] riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit

>> Since commit 5d8544e2d007 ("RISC-V: Generic library routines and 
>> assembly")
>> and commit ebcbd75e3962 ("riscv: Fix the bug in memory access fixup 
>> code"),
>> if __clear_user and __copy_user return from an fixup branch,
>> CSR_STATUS SR_SUM bit will be set, it is a vulnerability, so that
>> S-mode memory accesses to pages that are accessible by U-mode will 
>> success.
>> Disable S-mode access to U-mode memory should clear SR_SUM bit.
>>
>> Fixes: 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
>> Fixes: ebcbd75e3962 ("riscv: Fix the bug in memory access fixup code")
>>
>> Signed-off-by: Chen Lifu <chenlifu@...wei.com>
>> ---
>>   arch/riscv/lib/uaccess.S | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S
>> index 8c475f4da308..ec486e5369d9 100644
>> --- a/arch/riscv/lib/uaccess.S
>> +++ b/arch/riscv/lib/uaccess.S
>> @@ -173,11 +173,11 @@ ENTRY(__asm_copy_from_user)
>>       ret
>>       /* Exception fixup code */
>>   10:
>>       /* Disable access to user memory */
>> -    csrs CSR_STATUS, t6
>> +    csrc CSR_STATUS, t6
>>       mv a0, t5
>>       ret
>>   ENDPROC(__asm_copy_to_user)
>>   ENDPROC(__asm_copy_from_user)
>>   EXPORT_SYMBOL(__asm_copy_to_user)
>> @@ -225,10 +225,10 @@ ENTRY(__clear_user)
>>       j 3b
>>       /* Exception fixup code */
>>   11:
>>       /* Disable access to user memory */
>> -    csrs CSR_STATUS, t6
>> +    csrc CSR_STATUS, t6
>>       mv a0, a1
>>       ret
>>   ENDPROC(__clear_user)
>>   EXPORT_SYMBOL(__clear_user)
>>
> 
> friendly ping ...
> 

friendly ping ...

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> linux-riscv@...ts.infradead.org
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