netdev - Re: [PATCH rdma-next 3/6] RDMA/ucontext: Do not allow BAR mappings to be executable

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Date:   Thu, 18 Apr 2019 04:01:28 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Ruhl, Michael J" <michael.j.ruhl@...el.com>,
        Leon Romanovsky <leon@...nel.org>,
        Doug Ledford <dledford@...hat.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Feras Daoud <ferasda@...lanox.com>,
        Haggai Eran <haggaie@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next 3/6] RDMA/ucontext: Do not allow BAR mappings
 to be executable

On Thu, Apr 18, 2019 at 01:30:07AM -0500, Kees Cook wrote:

> Anything running with READ_IMPLIES_EXEC (i.e. a gnu stack marked WITH
> execute) should be considered broken. Now, the trouble is that this
> personality flag is carried across execve(), so if you have a launcher
> that doesn't fix up the personality for children, you'll see this
> spread all over your process tree. What is doing rdma mmap calls with
> an executable stack? That really feels to me like the real source of
> the problem.

Apparently the Fortran runtime forces the READ_IMPLIES_EXEC and
requires it for some real reason or another - Fortran and RDMA go
together in alot of cases.
 
> Is the file for the driver coming out of /dev? Seems like that should
> be mounted noexec and it would solve this too. (Though now I wonder
> why /dev isn't noexec by default? /dev/pts is noexec...

Yes - maybe?
 
> Regardless, if you wanted to add a "ignore READ_IMPLIES_EXEC" flag to
> struct file, maybe this bit could be populated by drivers?

This would solve our problem.. How about a flag in struct
file_operations?

Do you agree it is worth drivers banning VM_EXEC for these truely
non-executable pages?

Thanks,
Jason