linux-kernel - Re: [Xen-devel] [PATCH] xen/privcmd: fix static checker warning

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Date:   Thu, 7 Jun 2018 16:03:05 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Paul Durrant <Paul.Durrant@...rix.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [Xen-devel] [PATCH] xen/privcmd: fix static checker warning

On 07/06/18 13:23, Paul Durrant wrote:
>> -----Original Message-----
>> From: Andrew Cooper
>> Sent: 07 June 2018 11:28
>> To: Paul Durrant <Paul.Durrant@...rix.com>; xen-devel@...ts.xenproject.org;
>> linux-kernel@...r.kernel.org
>> Cc: Juergen Gross <jgross@...e.com>; Boris Ostrovsky
>> <boris.ostrovsky@...cle.com>; Dan Carpenter
>> <dan.carpenter@...cle.com>
>> Subject: Re: [Xen-devel] [PATCH] xen/privcmd: fix static checker warning
>>
>> On 07/06/18 11:21, Paul Durrant wrote:
>>> Commit 3ad0876554ca ("xen/privcmd: add
>> IOCTL_PRIVCMD_MMAP_RESOURCE")
>>> introduced a static checker warning:
>>>
>>>   drivers/xen/privcmd.c:827 privcmd_ioctl_mmap_resource()
>>>   warn: passing casted pointer 'pfns' to 'xen_remap_domain_mfn_array()'
>>>         64 vs 32.
>>>
>>> caused by this cast:
>>>
>>>    827  num = xen_remap_domain_mfn_array(vma,
>>>    828                                   kdata.addr & PAGE_MASK,
>>>    829                                   pfns, kdata.num, (int *)pfns,
>>>                                                           ^^^^^^^^^^^
>>>
>>> The reason for the cast is that xen_remap_domain_mfn_array() requires
>> an
>>> array of ints to store error codes. It is actually safe to re-use the
>>> pfns array for this purpose but it does look odd (as well as leading to
>>> the warning). It would also be easy for a future implementation change
>>> to make this re-use unsafe so this patch modifies privcmd to use a
>>> separately allocated array for error codes.
>>>
>>> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
>>> Signed-off-by: Paul Durrant <paul.durrant@...rix.com>
>>
>> It may be safe to reuse pfns[] as the storage space for the errs array,
>> but code is incorrect when sizeof(pfn) != sizeof(int).  In such a case,
>> you skip over every other err, and second half of pfns[] is junk from
>> the point of view of the errs loop.
>>
> 
> Yep, that is indeed what happens without this patch.

Can you please update the commit message accordingly?


Juergen