Re: [PATCH net-next] x86: bpf_jit_comp: secure bpf jit against sprayingattacks

[Daniel Borkmann]

On 05/20/2013 10:51 AM, David Laight wrote:
> > hpa bringed into my attention some security related issues
> > with BPF JIT on x86.
> >
> > This patch makes sure the bpf generated code is marked read only,
> > as other kernel text sections.
> >
> > It also splits the unused space (we vmalloc() and only use a fraction of
> > the page) in two parts, so that the generated bpf code not starts at a
> > known offset in the page, but a pseudo random one.
> ...
> > +static struct bpf_binary_header *bpf_alloc_binary(unsigned int proglen,
> > +						  u8 **image_ptr)
> ...
> > +	/* insert a random number of int3 instructions before BPF code */
> > +	*image_ptr = &header->image[prandom_u32() % hole];
> > +	return header;
> > +}
>
> Hmmm.... anyone looking to overwrite kernel code will then start
> looking for blocks of 0xcc bytes and know that what follows
> is the beginning of a function.
> That isn't any harder than random writes.
>
> Copying a random part of .rodata might be better - especially
> if you can find part of .rodata.str*.

Here seems also to be another approach ...

  http://grsecurity.net/~spender/jit_prot.diff

via: http://www.reddit.com/r/netsec/comments/13dzhx/linux_kernel_jit_spray_for_smep_kernexec_bypass/
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