Stas Sergeev wrote:
Hi,
Zachary Amsden wrote:
You need to get a #GP or #NP on the faulting iret. Several ways to
do that -
I do that much simpler - I provoke a SIGSEGV and in a signal handler
I put the wrong value to scp->cs or scp->ss, and that makes iret to
fault.
Ok, that's a new trick ;)
iret faults, but doesn't pop the user return frame.
But does it push the kernel frame after it or not?
If not - I don't understand how we go to a fixup.
If yes - I don't understand how the user's frame gets
accessed later, as it is above the kernel's frame.
Yes. The iret faults, the fault pushes a new kernel frame - and the
fault handler's iret returns, removing the kernel frame. So the kernel
frame is gone by the time the fixup runs.
safe limit is regs->esp + THREAD_SIZE*2... Well, may just I not do
that please? :)
For what, btw? There are no such a things for __KERNEL_DS or
anything, so
I just don't see the necessity.
It helps track down any bugs that could leak through otherwise and
corrupt random memory.
I think regs->esp + THREAD_SIZE*2 is already very permissive,
and I'd like to avoid messing with granularity. So unless you
really insist, I'll better not do that. :)
It's really hard to catch bugs that could otherwise happen when a
non-zero based stack gets used (for example, C code which uses %ebp with
-fomit-frame-pointer). Setting the limit to THREAD_SIZE should
guarantee that the non-zero based stack never is used to access anything
but the stack and current thread.
Zach
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
