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    SubjectRe: [PATCH v5 07/17] arm64: add basic pointer authentication support
    Hi all,

    On Fri, Oct 19, 2018 at 12:24:04PM +0100, Will Deacon wrote:
    > On Fri, Oct 19, 2018 at 12:15:43PM +0100, Catalin Marinas wrote:
    > > On Fri, Oct 05, 2018 at 09:47:44AM +0100, Kristina Martsenko wrote:
    > > > diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
    > > > new file mode 100644
    > > > index 000000000000..2aefedc31d9e
    > > > --- /dev/null
    > > > +++ b/arch/arm64/include/asm/pointer_auth.h
    > > > @@ -0,0 +1,63 @@
    > > > +// SPDX-License-Identifier: GPL-2.0
    > > > +#ifndef __ASM_POINTER_AUTH_H
    > > > +#define __ASM_POINTER_AUTH_H
    > > > +
    > > > +#include <linux/random.h>
    > > > +
    > > > +#include <asm/cpufeature.h>
    > > > +#include <asm/sysreg.h>
    > > > +
    > > > +#ifdef CONFIG_ARM64_PTR_AUTH
    > > > +/*
    > > > + * Each key is a 128-bit quantity which is split across a pair of 64-bit
    > > > + * registers (Lo and Hi).
    > > > + */
    > > > +struct ptrauth_key {
    > > > + unsigned long lo, hi;
    > > > +};
    > > > +
    > > > +/*
    > > > + * We give each process its own instruction A key (APIAKey), which is shared by
    > > > + * all threads. This is inherited upon fork(), and reinitialised upon exec*().
    > > > + * All other keys are currently unused, with APIBKey, APDAKey, and APBAKey
    > > > + * instructions behaving as NOPs.
    > > > + */
    > >
    > > I don't remember the past discussions but I assume the tools guys are ok
    > > with a single key shared by multiple threads. Ramana, could you ack this
    > > part, FTR?
    > >
    > > (and it would help if someone from the Android and Chrome camps can
    > > confirm)
    >
    > 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).

    Will

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