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Subject: Re: [PATCH 5/5] arm64/vdso: Restrict splitting VVAR VMA
To:     Andrei Vagin <avagin@gmail.com>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Dmitry Safonov <dima@arista.com>
References: <20200204175913.74901-1-avagin@gmail.com>
 <20200204175913.74901-6-avagin@gmail.com>
 <df8fa53c-5c21-b620-0254-ffefdd3a8834@arm.com>
 <20200223233013.GB349924@gmail.com>
From:   Vincenzo Frascino <vincenzo.frascino@arm.com>
Message-ID: <248ddd41-d3b3-05f2-4e49-177236726209@arm.com>
Date:   Mon, 24 Feb 2020 10:08:08 +0000
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Hi Andrei,

On 2/23/20 11:30 PM, Andrei Vagin wrote:
[...]

> 
> Hmmm. I have read the code of special_mapping_mremap() and I don't see where
> it restricts splitting the vvar mapping.
> 
> Here is the code what I see in the source:
> 
> static int special_mapping_mremap(struct vm_area_struct *new_vma)
> {
>         struct vm_special_mapping *sm = new_vma->vm_private_data;
> 
>         if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
>                 return -EFAULT;
> 
>         if (sm->mremap)
>                 return sm->mremap(sm, new_vma);
> 
>         return 0;
> }
> 
> And I have checked that without this patch, I can remap only one page of
> the vvar mapping.
>

I checked it a second time and I agree. The check on new_size is required in
this case.

> Thanks,
> Andrei
> 

-- 
Regards,
Vincenzo