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

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Date:	Fri, 17 May 2013 15:22:46 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
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

On Fri, 2013-05-17 at 14:19 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Thu, 16 May 2013 22:45:30 -0700
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > It looks like we can call module_free()/vfree() from softirq context,
> > so no longer need a wrapper and a work_struct.
> > 
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> 
> Applied.

Thanks David

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)



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.



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