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    SubjectRe: [RFC][PATCH] Randomize kernel base address on boot
    On Fri, 2011-05-27 at 08:42 -0700, Linus Torvalds wrote:
    > On Thu, May 26, 2011 at 3:18 PM, Rafael J. Wysocki <> wrote:
    > >
    > > Well, as far as I can tell, this feature is going to break hibernation on
    > > both x86_32 and x86_64 at the moment, unless you can guarantee that the
    > > randomized kernel location will be the same for both the boot and the target
    > > kernels.
    > You know what? Maybe that guarantee is actually the *right* thing to do..
    > In other words, maybe we really really shouldn't randomize the kernel
    > load address at boot time at all.
    > Instead, what would be much better, is if we just had some way to
    > re-link distro kernels with some random text offset. Sure, the load
    > address wouldn't be "random" in any local sense any more, but I think
    > the real effort here was to avoid having the common distro kernels
    > having known text addresses.
    > If you compile your own kernel version, you're already home free, and
    > load-time randomization is pointless.
    > And load-time randomization has all these nasty problems with memory
    > maps etc, because we obviously have to shift the whole kernel around
    > by some fixed offset. But if there was some way to just re-link the
    > distro kernel easily, then it could be done by the kernel install
    > scripts, and it could potentially do more than just "shift up load
    > address by some random number".
    > Hmm?
    > Linus

    You know what...I'm surprised that I'm saying this, but given the number
    of non-trivial challenges that still need to be solved in order to
    implement load-time randomization, maybe this would be a better way

    We'd still need to go through the same effort to hide information about
    kernel text offsets, and we'd still need to do per-cpu IDTs, but neither
    of those items are as challenging as some of the other problems.

    I'm not ready to take load-time randomization off the table, but I'd
    certainly like to hear more discussion on this. There are clearly
    advantages to load-time randomization that this new option wouldn't
    have, but the question is really "is what we gain worth the effort?".


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