On Wed, Jan 18, 2012 at 5:06 PM, Indan Zupancic <indan@xxxxxx> wrote: > On Wed, January 18, 2012 02:01, Andrew Lutomirski wrote: >> On Tue, Jan 17, 2012 at 4:56 PM, Indan Zupancic <indan@xxxxxx> wrote: >> I don't know what your ptrace jailer does. But a task can switch >> itself between 32-bit and 64-bit execution at will, and there's >> nothing the kernel can do about it. (That isn't quite true -- in >> theory the kernel could fiddle with the GDT, but that would be >> expensive and wouldn't work on Xen.) > > That's why we don't cache the CS value but check it for every system call. > But you said elsewhere that checking CS isn't always correct either. > I grepped arch/x86 for "user_64bit_mode", but couldn't find anything, > but maybe my kernel sources are too old, I haven't updated this system > for almost a year. The current code only handles 0x23 and 0x33 and kills > the jail if it encounters anything else. I think you're hosed on Xen, then. Xen regularly runs with a different Xen-specific cs value. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
