linux-kernel - Re: [PATCH v2 13/22] iommufd: Add mmap interface

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Message-ID: <aBzmW6A6mZAbcbze@nvidia.com>
Date: Thu, 8 May 2025 10:14:03 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: "Tian, Kevin" <kevin.tian@...el.com>, Pranjal Shrivastava
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Subject: Re: [PATCH v2 13/22] iommufd: Add mmap interface

On Thu, May 08, 2025 at 09:12:08AM -0300, Jason Gunthorpe wrote:
> On Thu, May 08, 2025 at 09:15:47AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Thursday, May 8, 2025 11:50 AM
> > > 
> > > On Wed, May 07, 2025 at 07:08:09PM -0300, Jason Gunthorpe wrote:
> > > > On Wed, May 07, 2025 at 02:09:31PM -0700, Nicolin Chen wrote:
> > > > > I have another question: while I don't think my code is handling
> > > > > this well either, how should we validate the input address is an
> > > > > allowed one?
> > > >
> > > > The pgoff to mmap? If it isn't in the maple tree it is not allowed, if
> > > > it isn't at the start of range it is not allowed, if the size is not
> > > > exactly the same as the range it is not allowed.
> > > 
> > > Kevin suggested to allow a partial mmap, i.e allow the size to be
> > > smaller than what the cookie describes. Yet, surely the mmap size
> > > should not above the allocated size.
> > > 
> > 
> > let me clarify - I didn't suggested it. Instead it's what the code 
> > does hence I suggested to make it explicit. 😊
> 
> It is probably reasonable to require the pgoff to be at the start but
> allow a shorter map, for forward compatability.
> 
> But also, you could add flags to the ioctl creating the mmap to
> request future bigger sizes.
> 
> There is some appeal to be more strict to make misuse less likely..

OK. Let's strict the size to be exact.

Thanks
Nicolin