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From: Will Deacon <will.deacon@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	Andrew Jones <drjones@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Jacob Bramley <jacob.bramley@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Adam Wallis <awallis@codeaurora.org>,
	"Suzuki K . Poulose" <suzuki.poulose@arm.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	Kristina Martsenko <kristina.martsenko@arm.com>,
	Dave P Martin <Dave.Martin@arm.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>,
	Amit Kachhap <Amit.Kachhap@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v5 07/17] arm64: add basic pointer authentication support
Date: Fri, 19 Oct 2018 17:16:51 +0100
Message-ID: <20181019161651.GE16771@arm.com> (raw)
In-Reply-To: <CAGXu5jK8OK+430FQtztwVD8B95_SCjTWoysZXBdkZaDeSiV+ow@mail.gmail.com>

On Fri, Oct 19, 2018 at 09:05:57AM -0700, Kees Cook wrote:
> On Fri, Oct 19, 2018 at 8:49 AM, Will Deacon <will.deacon@arm.com> wrote:
> > On Fri, Oct 19, 2018 at 08:36:45AM -0700, Kees Cook wrote:
> >> On Fri, Oct 19, 2018 at 4:24 AM, Will Deacon <will.deacon@arm.com> 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.
> >>
> >> Oh CRIU. Yikes. I'd like the get/set to be gated by the CONFIG, yes.
> >> No reason to allow explicit access to the key (and selected algo) if
> >> we don't have to.
> >
> > Makes sense.
> >
> >> As for per-thread or not, having a "pick a new key now" prctl() sounds
> >> good, but I'd like to have an eye toward having it just be "automatic"
> >> on clone().
> >
> > I thought about that too, but we're out of clone() flags afaict and there's
> > no arch hook in there. We could add yet another clone syscall, but yuck (and
> > I reckon viro would kill us).
> >
> > Or are you saying that we could infer the behaviour from the existing set
> > of flags?
> 
> I mean if it's starting a new thread, it should get a new key
> automatically, just like the ssp canary happens in dup_task_struct().
> 
> (Or did I miss some context for why that's not possible?)

The problem with that is if the child thread (in userspace) returns from
the function that called fork(), then it will explode because the link
register will have been signed with the parent key.

Will

  reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-05  8:47 [PATCH 00/17] ARMv8.3 " Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 01/17] arm64: add pointer authentication register bits Kristina Martsenko
2018-10-11 16:28   ` Will Deacon
2018-10-12  8:53     ` Mark Rutland
2018-10-12  8:56       ` Will Deacon
2018-10-12  9:50         ` Mark Rutland
2018-10-05  8:47 ` [PATCH v5 02/17] arm64/kvm: consistently handle host HCR_EL2 flags Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 03/17] arm64/kvm: hide ptrauth from guests Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 04/17] arm64: Don't trap host pointer auth use to EL2 Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 05/17] arm64/cpufeature: detect pointer authentication Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 06/17] asm-generic: mm_hooks: allow hooks to be overridden individually Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 07/17] arm64: add basic pointer authentication support Kristina Martsenko
2018-10-11 16:00   ` Suzuki K Poulose
2018-10-19 11:15   ` Catalin Marinas
2018-10-19 11:24     ` Will Deacon
2018-10-19 15:36       ` Kees Cook
2018-10-19 15:49         ` Will Deacon
2018-10-19 16:05           ` Kees Cook
2018-10-19 16:16             ` Will Deacon [this message]
2018-10-19 15:54         ` Mark Rutland
2018-10-19 16:49       ` Cyrill Gorcunov
2018-11-14 18:11       ` Will Deacon
2018-11-15 10:25         ` Dave Martin
2018-10-23  8:36     ` Ramana Radhakrishnan
2018-10-23 10:20       ` Will Deacon
2018-10-05  8:47 ` [PATCH v5 08/17] arm64: expose user PAC bit positions via ptrace Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 09/17] arm64: perf: strip PAC when unwinding userspace Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 10/17] arm64: enable pointer authentication Kristina Martsenko
2018-10-05  8:47 ` [PATCH v5 11/17] arm64: docs: document " Kristina Martsenko
2018-10-05  9:04   ` Ramana Radhakrishnan
2018-10-16 16:14     ` Kristina Martsenko
2018-10-19 11:35       ` Catalin Marinas
2018-10-19 11:47         ` Marc Zyngier
2018-10-19 12:22         ` Will Deacon
2018-10-19 14:42         ` Kristina Martsenko
2018-10-19 15:10           ` Catalin Marinas
2018-10-19 17:45             ` Will Deacon
2018-11-02  6:02               ` Jon Masters
2018-10-24 10:56         ` Ramana Radhakrishnan
2018-10-15 22:35   ` Kees Cook
2018-11-02  9:46     ` Ramana Radhakrishnan
2018-10-05  8:47 ` [RFC 12/17] arm64: move ptrauth keys to thread_info Kristina Martsenko
2018-10-19 11:38   ` Catalin Marinas
2018-10-05  8:47 ` [RFC 13/17] arm64: install user ptrauth keys at kernel exit time Kristina Martsenko
2018-10-05  8:47 ` [RFC 14/17] arm64: unwind: strip PAC from kernel addresses Kristina Martsenko
2018-10-05  8:47 ` [RFC 15/17] arm64: enable ptrauth earlier Kristina Martsenko
2018-10-06 12:51   ` Amit Kachhap
2018-10-05  8:47 ` [RFC 16/17] arm64: initialize and switch ptrauth kernel keys Kristina Martsenko
2018-10-06 12:56   ` Amit Kachhap
2018-10-05  8:47 ` [RFC 17/17] arm64: compile the kernel with ptrauth -msign-return-address Kristina Martsenko
2018-10-05  9:01   ` Ramana Radhakrishnan
2018-10-11 14:00     ` Kristina Martsenko
2018-10-11 14:23   ` Vladimir Murzin
2018-10-15 22:38     ` Kees Cook
2018-10-15 22:42 ` [PATCH 00/17] ARMv8.3 pointer authentication support Kees Cook
2018-11-13 16:17   ` Kristina Martsenko
2018-11-13 23:09     ` Kees Cook
2018-11-14 15:54       ` Kristina Martsenko
2018-11-14 21:47       ` Mark Rutland
2018-11-14 22:48         ` Kees Cook
2018-10-19 12:36 ` Will Deacon
2018-10-23  8:39   ` Ramana Radhakrishnan

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