netdev - Re: [PATCH net-next] x86: bpf_jit_comp: can call module

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Date:	Fri, 17 May 2013 18:29:35 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, viro@...IV.linux.org.uk
Subject: Re: [PATCH net-next] x86: bpf_jit_comp: can call module_free()
 from any context

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 17 May 2013 15:22:46 -0700

> I am considering adding ReadOnly protection to the pages containing BPF
> generated code, like we do for modules text if
> CONFIG_DEBUG_SET_MODULE_RONX=y
> 
> Should we have an option to configure this, driven by HAVE_BPF_JIT_RO,
> or should we do the RO thing in all cases (ie not adding yet another
> Kconfig stuff)

I think we should do this unconditionally, it'll be noise as far as
overhead during filter compilation.

> Another ongoing work is to add some protection against BPF JIT spraying
> attacks
> ( http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html )
> 
> My idea would be to have a hole of random size before the code, filled
> with 0xcc (int3) opcodes. Since we allocate a multiple of PAGE_SIZE
> anyway, we have plenty of available space to play with.

This sounds like a good idea too.
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