From: Marc Zyngier <maz@kernel.org>
To: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Kees Cook <keescook@chromium.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Kristina Martsenko <kristina.martsenko@arm.com>,
Dave Martin <Dave.Martin@arm.com>,
Mark Brown <broonie@kernel.org>,
Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>,
Amit Kachhap <amit.kachhap@arm.com>,
Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 00/18] arm64: return address signing
Date: Thu, 12 Mar 2020 17:31:36 +0000 [thread overview]
Message-ID: <87945e6110511caaceeb3f1294b6f88f@kernel.org> (raw)
In-Reply-To: <bd76de32-12c5-fcbe-25d2-c501f9491bee@arm.com>
Hi James,
On 2020-03-12 17:26, James Morse wrote:
> Hi Amit, Marc,
>
> On 12/03/2020 15:05, Marc Zyngier wrote:
>> On 2020-03-12 13:21, Amit Kachhap wrote:
>>> On 3/12/20 6:17 PM, Marc Zyngier wrote:
>>>> On 2020-03-12 08:06, Amit Kachhap wrote:
>>>>> On 3/12/20 12:23 PM, Amit Kachhap wrote:
>>>>>> On 3/11/20 2:58 PM, James Morse wrote:
>>>>>>> On 3/6/20 6:35 AM, Amit Daniel Kachhap wrote:
>>>>>>>> This series improves function return address protection for the
>>>>>>>> arm64 kernel, by
>>>>>>>> compiling the kernel with ARMv8.3 Pointer Authentication
>>>>>>>> instructions (referred
>>>>>>>> ptrauth hereafter). This should help protect the kernel against
>>>>>>>> attacks using
>>>>>>>> return-oriented programming.
>>>>>>>
>>>>>>> (as it looks like there may be another version of this:)
>>>>>>>
>>>>>>> Am I right in thinking that after your patch 10 changing
>>>>>>> cpu_switch_to(), only the A key is live during kernel execution?
>>>>>>
>>>>>> Yes
>
>>>>>>> KVM is still save/restoring 4 extra keys around guest-entry/exit.
>>>>>>> As you
>>>>>>> restore all the keys on return to user-space, is this still
>>>>>>> necessary?
>>>>>>
>>>>>> Yes Its a good optimization to skip 4 non-A keys. I was wondering
>>>>>> whether to do it in
>>>>>> this series or send it separately.
>>>>>
>>>>> I suppose we can only skip non-A keys save/restore for host
>>>>> context. If
>>>>> we skip non-A keys for guest context then guest with old
>>>>> implementation
>>>>> will break. Let me know your opinion.
>>>>
>>>> I don't think you can skip anything as far as the guest is
>>>> concerned.
>>>> But being able to skip the B keys (which is what I expect you call
>>>> the
>>>> non-A keys) on the host would certainly be useful.
>
>> But if KVM doesn't save/restore the host's B-keys in the world switch,
>> then you must make sure that no host userspace can make use of them,
>> as they would be the guest's keys.
>
> Yes, the arch code entry.S changes cover this with
> ptrauth_keys_install_user. It restores
> 4 keys, and the generic key.
>
>
> We always need to save/restore all the guest keys (as we do today).
> But when ptrauth_restore_state restores the host keys, it only needs
> to restore the one
> the kernel uses. (possibly using the same macro's so it stays up to
> date?!)
>
> If we return to user-space, the arch code's entry code does the right
> thing.
> KVM's user-space peeking at the keys will see the saved values.
>
>
> My original question was more around: do we need to do this now, or
> can we clean it up in
> a later kernel version?
>
> (and a sanity check that it doesn't lead to a correctness problem)
I think what we have now is sane, and doesn't seem to lead to any
issue (at least that I can see). We can always optimize this at a
later point.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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prev parent reply other threads:[~2020-03-12 17:31 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-06 6:35 [PATCH v6 00/18] arm64: return address signing Amit Daniel Kachhap
2020-03-06 6:35 ` [PATCH v6 01/18] arm64: cpufeature: Fix meta-capability cpufeature check Amit Daniel Kachhap
2020-03-10 10:59 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 02/18] arm64: cpufeature: add pointer auth meta-capabilities Amit Daniel Kachhap
2020-03-10 11:18 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 03/18] arm64: rename ptrauth key structures to be user-specific Amit Daniel Kachhap
2020-03-10 11:35 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 04/18] arm64: install user ptrauth keys at kernel exit time Amit Daniel Kachhap
2020-03-06 19:07 ` James Morse
2020-03-10 11:48 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 05/18] arm64: create macro to park cpu in an infinite loop Amit Daniel Kachhap
2020-03-10 12:02 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 06/18] arm64: ptrauth: Add bootup/runtime flags for __cpu_setup Amit Daniel Kachhap
2020-03-06 19:07 ` James Morse
2020-03-09 17:04 ` Catalin Marinas
2020-03-10 12:14 ` Vincenzo Frascino
2020-03-11 9:28 ` Amit Kachhap
2020-03-06 6:35 ` [PATCH v6 07/18] arm64: cpufeature: Move cpu capability helpers inside C file Amit Daniel Kachhap
2020-03-10 12:20 ` Vincenzo Frascino
2020-03-10 12:53 ` Amit Kachhap
2020-03-11 10:50 ` Catalin Marinas
2020-03-11 11:44 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 08/18] arm64: cpufeature: handle conflicts based on capability Amit Daniel Kachhap
2020-03-10 12:31 ` Vincenzo Frascino
2020-03-11 11:03 ` Catalin Marinas
2020-03-11 11:46 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 09/18] arm64: enable ptrauth earlier Amit Daniel Kachhap
2020-03-10 15:45 ` Vincenzo Frascino
2020-03-11 6:26 ` Amit Kachhap
2020-03-11 10:26 ` Vincenzo Frascino
2020-03-11 10:46 ` Amit Kachhap
2020-03-11 10:49 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 10/18] arm64: initialize and switch ptrauth kernel keys Amit Daniel Kachhap
2020-03-10 15:07 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 11/18] arm64: initialize ptrauth keys for kernel booting task Amit Daniel Kachhap
2020-03-10 15:09 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 12/18] arm64: mask PAC bits of __builtin_return_address Amit Daniel Kachhap
2020-03-06 19:07 ` James Morse
2020-03-09 12:27 ` Amit Kachhap
2020-03-06 6:35 ` [PATCH v6 13/18] arm64: unwind: strip PAC from kernel addresses Amit Daniel Kachhap
2020-03-09 19:03 ` James Morse
2020-03-10 12:28 ` Amit Kachhap
2020-03-10 17:37 ` James Morse
2020-03-11 6:07 ` Amit Kachhap
2020-03-11 9:09 ` James Morse
2020-03-06 6:35 ` [PATCH v6 14/18] arm64: __show_regs: strip PAC from lr in printk Amit Daniel Kachhap
2020-03-10 15:11 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 15/18] arm64: suspend: restore the kernel ptrauth keys Amit Daniel Kachhap
2020-03-10 15:18 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 16/18] kconfig: Add support for 'as-option' Amit Daniel Kachhap
2020-03-06 11:37 ` Masahiro Yamada
2020-03-06 11:49 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 17/18] arm64: compile the kernel with ptrauth return address signing Amit Daniel Kachhap
2020-03-10 15:20 ` Vincenzo Frascino
2020-03-06 6:35 ` [PATCH v6 18/18] lkdtm: arm64: test kernel pointer authentication Amit Daniel Kachhap
2020-03-10 15:59 ` [PATCH v6 00/18] arm64: return address signing Rémi Denis-Courmont
2020-03-11 9:28 ` James Morse
2020-03-12 6:53 ` Amit Kachhap
2020-03-12 8:06 ` Amit Kachhap
2020-03-12 12:47 ` [PATCH v6 00/18] (as long a Marc Zyngier
2020-03-12 13:21 ` Amit Kachhap
2020-03-12 15:05 ` [PATCH v6 00/18] arm64: return address signing Marc Zyngier
2020-03-12 17:26 ` James Morse
2020-03-12 17:31 ` Marc Zyngier [this message]
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