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

From: Jason Gunthorpe <[email-masked]>
Date: Thu, 18 Apr 2019 04:01:28 -0300

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