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Re: RFC: Longjmp vs LD_POINTER_GUARD revisited
On Sun, Nov 15, 2009 at 10:29:33AM -0800, Paul Pluzhnikov wrote:
> On Sun, Nov 15, 2009 at 9:34 AM, Daniel Jacobowitz <drow@false.org> wrote:
>
> > * Where the jmp_buf contents are obfuscated, as done by glibc, which
> > "encrypts" them using a canary stored in the thread TCB.
>
> FWIW, I never understood the point of this obfuscation: the program
> (and any rogue code injected into it) can trivially discover the value
> of canary:
>
> call sigsetjmp
> a_label:
> ... canary = sigjmp_buf.__jmpbuf[JB_PC] - &a_label
>
> I think GDB could also perform such discovery, and that would allow it
> work with non-debug glibc (debug glibc (I believe) is exception rather
> the rule outside of {gdb,glibc,gcc} developers).
There's a rotate and an xor involved; I don't believe this would work
as written... sure, we could "discover" it from disassembling key
functions automatically...
--
Daniel Jacobowitz
CodeSourcery