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    SubjectRe: [PATCH v5 07/17] arm64: add basic pointer authentication support
    On Wed, Nov 14, 2018 at 06:11:39PM +0000, Will Deacon wrote:

    [...]

    > On Fri, Oct 19, 2018 at 12:24:04PM +0100, Will Deacon wrote:

    [...]

    > > FWIW: I think we should be entertaining a prctl() interface to use a new
    > > key on a per-thread basis. Obviously, this would need to be used with care
    > > (e.g. you'd fork(); use the prctl() and then you'd better not return from
    > > the calling function!).
    > >
    > > Assuming we want this (Kees -- I was under the impression that everything in
    > > Android would end up with the same key otherwise?), then the question is
    > > do we want:
    > >
    > > - prctl() get/set operations for the key, or
    > > - prctl() set_random_key operation, or
    > > - both of the above?
    > >
    > > Part of the answer to that may lie in the requirements of CRIU, where I
    > > strongly suspect they need explicit get/set operations, although these
    > > could be gated on CONFIG_CHECKPOINT_RESTORE=y.
    >
    > I managed to speak to the CRIU developers at LPC. The good news is that
    > their preference is for a ptrace()-based interface for getting and setting
    > the keys, so the only prctl() operation we need is to set a random key
    > (separately for A and B).

    That's good if it works for them, and it seems the cleaner approach.

    _If_ they run the new thread up to a checkpoint, restoring the memory
    and doing all the setup that requires in-thread syscalls, then stop it
    in ptrace to finally inject the regs, then it makes sense to set the
    keys at that stop -- i.e., you set the keys atomically* with the final
    setting of the thread's PC.

    (* with respect to the target thread)

    So long as you're confident they've understood the implications of
    ptrauth for CRIU, I guess this can work.


    (In other news, they will also need to do some work to support SVE, but
    that's unrelated to ptrauth.)

    Cheers
    ---Dave

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