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Subject: Re: [PATCH] Fix compat regression in process_vm_rw()
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>, Kyle Huey <me@kylehuey.com>
References: <f69575e0-5170-2d51-8d74-8b3453723aa3@kernel.dk>
 <20201027191920.GA262123@centos.familie-tometzki.de>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <43252884-dcf2-fe13-23ce-765f97e86579@kernel.dk>
Date:   Tue, 27 Oct 2020 13:32:30 -0600
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On 10/27/20 1:19 PM, damian wrote:
> On Mo, 26. Okt 18:03, Jens Axboe wrote:
>> The removal of compat_process_vm_{readv,writev} didn't change
>> process_vm_rw(), which always assumes it's not doing a compat syscall.
>> Instead of passing in 'false' unconditionally for 'compat', make it
>> conditional on in_compat_syscall().
>>
>> Fixes: c3973b401ef2 ("mm: remove compat_process_vm_{readv,writev}")
>> Reported-by: Kyle Huey <me@kylehuey.com>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> ---
>>
>> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
>> index fd12da80b6f2..05676722d9cd 100644
>> --- a/mm/process_vm_access.c
>> +++ b/mm/process_vm_access.c
>> @@ -273,7 +273,8 @@ static ssize_t process_vm_rw(pid_t pid,
>>  		return rc;
>>  	if (!iov_iter_count(&iter))
>>  		goto free_iov_l;
>> -	iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r, false);
>> +	iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
>> +				in_compat_syscall());
>>  	if (IS_ERR(iov_r)) {
>>  		rc = PTR_ERR(iov_r);
>>  		goto free_iov_l;
>>
>> -- 
>> Jens Axboe
>>
> Hello Jens,
> 
> i got the following error when i try to build. 
> 
> m/process_vm_access.c: In Funktion »process_vm_rw«:
> mm/process_vm_access.c:277:5: Fehler: Implizite Deklaration der Funktion »in_compat_syscall«; meinten Sie »in_ia32_syscall«? [-Werror=implicit-function-declaration]
>   277 |     in_compat_syscall());
>       |     ^~~~~~~~~~~~~~~~~
>       |     in_ia32_syscall

Yeah, sorry about that. Geert sent out a fix:

https://lore.kernel.org/lkml/20201027182246.651908-1-geert+renesas@glider.be/

-- 
Jens Axboe