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Message-ID: <0127a542-3f93-7bd0-e00d-4a0e49846c8f@kernel.dk>
Date: Mon, 26 Oct 2020 18:09:06 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Kyle Huey <me@...ehuey.com>,
open list <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@....de>,
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Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [REGRESSION] mm: process_vm_readv testcase no longer works after
compat_prcoess_vm_readv removed
On 10/26/20 6:05 PM, Al Viro wrote:
> On Mon, Oct 26, 2020 at 05:56:11PM -0600, Jens Axboe wrote:
>> On 10/26/20 4:55 PM, Kyle Huey wrote:
>>> A test program from the rr[0] test suite, vm_readv_writev[1], no
>>> longer works on 5.10-rc1 when compiled as a 32 bit binary and executed
>>> on a 64 bit kernel. The first process_vm_readv call (on line 35) now
>>> fails with EFAULT. I have bisected this to
>>> c3973b401ef2b0b8005f8074a10e96e3ea093823.
>>>
>>> It should be fairly straightforward to extract the test case from our
>>> repository into a standalone program.
>>
>> Can you check with this applied?
>>
>> 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());
>
> _ouch_
>
> There's a bug, all right, but I'm not sure that this is all there is
> to it. For now it's probably the right fix, but... Consider the fun
> trying to use that from 32bit process to access the memory of 64bit
> one. IOW, we might want to add an explicit flag for "force 64bit
> addresses/sizes in rvec".
Ouch yes good point, nice catch.
--
Jens Axboe
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