Message-ID: <1428931781.22575.232.camel@opteya.com>
Date:	Mon, 13 Apr 2015 15:29:41 +0200
From:	Yann Droneaud <ydroneaud@...eya.com>
To:	Haggai Eran <haggaie@...lanox.com>
Cc:	Shachar Raindel <raindel@...lanox.com>,
	Sagi Grimberg <sagig@...lanox.com>, linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: CVE-2014-8159 kernel: infiniband: uverbs: unprotected physical
 memory access

Hi,

Le jeudi 02 avril 2015 à 18:12 +0000, Haggai Eran a écrit :
> On Thursday, April 2, 2015 7:44 PM, Shachar Raindel wrote:
> >> -----Original Message-----
> >> From: Yann Droneaud [mailto:ydroneaud@...eya.com]
> >> Le jeudi 02 avril 2015 à 18:18 +0300, Haggai Eran a écrit :
> >> > On 02/04/2015 16:30, Yann Droneaud wrote:
> >> >> Le jeudi 02 avril 2015 à 10:52 +0000, Shachar Raindel a écrit :
> >> >>>> -----Original Message-----
> >> >>>> From: Yann Droneaud [mailto:ydroneaud@...eya.com]
> >> >>>> Sent: Thursday, April 02, 2015 1:05 PM
> >> >>>> Le mercredi 18 mars 2015 à 17:39 +0000, Shachar Raindel a écrit :
> >> >>
> >> >>>>> +      /*
> >> >>>>> +       * If the combination of the addr and size requested for this
> >> >>>> memory
> >> >>>>> +       * region causes an integer overflow, return error.
> >> >>>>> +       */
> >> >>>>> +      if ((PAGE_ALIGN(addr + size) <= size) ||
> >> >>>>> +          (PAGE_ALIGN(addr + size) <= addr))
> >> >>>>> +              return ERR_PTR(-EINVAL);
> >> >>>>> +
> >> >>>>
> >> >>>> Can access_ok() be used here ?
> >> >>>>
> >> >>>>          if (!access_ok(writable ? VERIFY_WRITE : VERIFY_READ,
> >> >>>>                         addr, size))
> >> >>>>                   return ERR_PTR(-EINVAL);
> >> >>>>
> >> >>>
> >> >>> No, this will break the current ODP semantics.
> >> >>>
> >> >>> ODP allows the user to register memory that is not accessible yet.
> >> >>> This is a critical design feature, as it allows avoiding holding
> >> >>> a registration cache. Adding this check will break the behavior,
> >> >>> forcing memory to be all accessible when registering an ODP MR.
> >> >>>
> >> >>
> >> >> Where's the check for the range being in userspace memory space,
> >> >> especially for the ODP case ?
> >> >>
> >> >> For non ODP case (eg. plain old behavior), does get_user_pages()
> >> >> ensure the requested pages fit in userspace region on all
> >> >> architectures ? I think so.
> >> >
> >> > Yes, get_user_pages will return a smaller amount of pages than
> >> requested
> >> > if it encounters an unmapped region (or a region without write
> >> > permissions for write requests). If this happens, the loop in
> >> > ib_umem_get calls get_user_pages again with the next set of pages, and
> >> > this time if it the first page still cannot be mapped an error is
> >> returned.
> >> >
> >> >>
> >> >> In ODP case, I'm not sure such check is ever done ?
> >> >
> >> > In ODP, we also call get_user_pages, but only when a page fault occurs
> >> > (see ib_umem_odp_map_dma_pages()). This allows the user to pre-
> >> register
> >> > a memory region that contains unmapped virtual space, and then mmap
> >> > different files into that area without needing to re-register.
> >> >
> >>
> >> OK, thanks for the description.
> >>
> >> ...
> >>
> >> Another related question: as the large memory range could be registered
> >> by user space with ibv_reg_mr(pd, base, size, IB_ACCESS_ON_DEMAND),
> >> what's prevent the kernel to map a file as the result of mmap(0, ...)
> >> in this  region, making it available remotely through IBV_WR_RDMA_READ /
> >> IBV_WR_RDMA_WRITE ?
> >>
> > 
> > This is not a bug. This is a feature.
> > 
> > Exposing a file through RDMA, using ODP, can be done exactly like this.
> > Given that the application explicitly requested this behavior, I don't
> > see why it is a problem. Actually, some of our tests use such flows.
> > The mmu notifiers mechanism allow us to do this safely. When the page is
> > written back to disk, it is removed from the ODP mapping. When it is
> > accessed by the HCA, it is brought back to RAM.
> > 
> 
> I want to add that we would like to see users registering a very large
> memory region (perhaps the entire process address space) for local
> access, and then enabling remote access only to specific regions using
> memory windows. However, this isn't supported yet by our driver.

In such scheme, the registration must still be handled "manually":
one has to create a memory window to get a rkey to be exchanged with
a peer, so why one would want to register such a large memory region
(the whole process space) ?

I guess creating the memory window is faster than registering memory
region. I'd rather say this is not an excuse to register a larger 
memory region (up to the whole process space, current and future) as it 
sounds like a surprising optimisation: let the HCA known too many
pages just to be sure it already knows some when the process want to 
use them. It seems it would become difficult to handle if there's too
many processes.

I would prefer creating memory region becoming costless (through ODP :).

>  Still, there are valid cases where you would still want the results
> of an mmap(0,...) call to be remotely accessible, in cases where there
> is enough trust between the local process and the remote process.

mmap(0, ...., fd) let the kernel choose where to put the file in 
process virtual memory space, so it may, may not, partially, end up in 
an ODP pre registered memory region for a range unallocated/unused yet.

I don't think one want such to happen.

>  It may help a middleware communication library register a large
> portion of the address space in advance, and still work with random
> pointers given to it by another application module.
> 

But as said in the beginnig of your message, the middleware would have
bind a memory window before posting work request / exposing rkey for
the "random pointers".

So I fail to understand how could be used ODP when it comes to 
registering a memory region not yet backed by something.

Regards.

-- 
Yann Droneaud
OPTEYA


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