Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate" eBPF instruction
From: Alexei Starovoitov <hidden>
Date: 2014-08-13 21:56:48
Also in:
linux-api, lkml
On Wed, Aug 13, 2014 at 2:38 PM, Alexei Starovoitov [off-list ref] wrote:
On Wed, Aug 13, 2014 at 2:27 PM, H. Peter Anvin [off-list ref] wrote:quoted
On 08/13/2014 02:23 PM, Andy Lutomirski wrote:quoted
On Wed, Aug 13, 2014 at 2:21 PM, H. Peter Anvin [off-list ref] wrote:quoted
One thing about this that may be a serious concern: allowing the user to control 8 contiguous bytes of kernel memory may be a security hazard.I'm confused. What kind of memory? I can control a lot more than 8 bytes of stack very easily. Or are you concerned about 8 contiguous bytes of *executable* memory?Yes. Useful for some kinds of ROP custom gadgets.I don't get it. What is ROP ? What is the concern about 8 bytes ?
looked it up. too many abbreviations now days. x64 jit spraying was fixed by Eric some time ago, so JIT emitting movabsq doesn't increase attack surface. various movs of 32-bit immediates can be used for 'custom gadget' just as well. Worst case JIT won't be enabled. In classic BPF we allow junk to be stored in used fields of 'struct sock_filter' and so far that wasn't a problem. eBPF is more paranoid regarding verification.