2008/10/28 Vlad Tsyrklevich <[EMAIL PROTECTED]>:
> I have been looking at Opty2Nop recently and I made a couple of changes.
>
> 1) Fixed a minor bug, sometimes Opty2 would generate C1 /6 instructions
> which most processors will execute but which are not technically valid (they
> would exist for SAL but SAL is an alias for SHL so it is defined as C1 /4).

Did you find any processors that wouldn't execute it?  I remember this
case, and I realized it was technically invalid, although I couldn't
find a processor that cared (and when you think about it, there is no
reason to care).

> 2) I changed the 0x90 nop instruction so that it is no longer considered
> that 0x90 changes the eax register.

Oh yeah, it's xchg eax, eax, I autogenerated those tables :\  Btw, has
anyone seen the original table generation code laying around?

> 3) Removed o16/0x66 prepend byte from 0x0f, this is currently unused anyways
> but might prevent some poor person from debugging it in the future.

Oh yeah, good catch

> 4) Previously short jumps would only make positive jumps, I added the
> capability for them to make a "-1" jump which would basically just start
> executing at the offset byte. For example it could generate something like
> EB FF XX YY ... where EB FF jumps to FF XX YY ...

Oh dang, smart.  And by positive I think you mean non-negative, since
it would generate for 0.

> 5) I added support for the instructions mov reg, segreg (8C), mov reg,
> imm8/imm32 (C6/C7), and lea reg, mem (8D). I implemented LEA so that it only
> allows memory references to be in ModR/M form and not be in SIB form (I
> don't think it's possible to allow SIB in the way Opty2 works at the
> moment).

Yeah, I don't think so either, the pivot tables are all based on 1
byte of context, and you would need 2 bytes of context for the SIB
byte.

>
> I tested this just running about 50,000 bytes worth of nops with different
> save register settings and it ran as expected.I believe that this should be
> good to go though I haven't actually tested this with any exploit modules!
> The svn diff of the opty2_tables.rb file is attached.

Word mannnn.  Nice work.  Thanks.

>
>  - Vlad Tsyrklevich
>
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