On Mon, Mar 04, 2019 at 04:38:18PM +0530, Amit Daniel Kachhap wrote:
>
> Hi Dave,
>
> On 3/1/19 4:54 PM, Dave P Martin wrote:
> >On Fri, Mar 01, 2019 at 10:37:54AM +0000, Amit Daniel Kachhap wrote:
> >>Hi,
> >>
> >>On 2/21/19 9:24 PM, Dave Martin wrote:
> >>>On Tue, Feb 19, 2019 at 02:54:31PM +0530, Amit Daniel Kachhap wrote:
> >
> >[...]
> >
> >>>>diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
> >>>>index 04be43d..2074684 100644
> >>>>--- a/arm/aarch64/include/kvm/kvm-config-arch.h
> >>>>+++ b/arm/aarch64/include/kvm/kvm-config-arch.h
> >>>>@@ -8,7 +8,9 @@
> >>>> "Create PMUv3 device"), \
> >>>> OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed, \
> >>>> "Specify random seed for Kernel Address Space " \
> >>>>- "Layout Randomization (KASLR)"),
> >>>>+ "Layout Randomization (KASLR)"), \
> >>>>+ OPT_BOOLEAN('\0', "ptrauth", &(cfg)->has_ptrauth, \
> >>>>+ "Enable address authentication"),
> >>>
> >>>Nit: doesn't this enable address *and* generic authentication? The
> >>>discussion on what capababilities and enables the ABI exposes probably
> >>>needs to conclude before we can finalise this here.
> >>ok.
> >>>
> >>>However, I would recommend that we provide a single option here that
> >>>turns both address authentication and generic authentication on, even
> >>>if the ABI treats them independently. This is expected to be the common
> >>>case by far.
> >>ok
> >>>
> >>>We can always add more fine-grained options later if it turns out to be
> >>>necessary.
> >>Mark suggested to provide 2 flags [1] for Address and Generic
> >>authentication so I was thinking of adding 2 features like,
> >>
> >>+#define KVM_ARM_VCPU_PTRAUTH_ADDR 4 /* CPU uses pointer address
> >>authentication */
> >>+#define KVM_ARM_VCPU_PTRAUTH_GENERIC 5 /* CPU uses pointer generic
> >>authentication */
> >>
> >>And supply both of them concatenated in VCPU_INIT stage. Kernel KVM
> >>would expect both feature requested together.
> >
> >Seems reasonable. Do you mean the kernel would treat it as an error if
> >only one of these flags is passed to KVM_ARM_VCPU_INIT, or would KVM
> >simply treat them as independent?
> If both flags are passed together then only start using ptrauth otherwise
> keep ptrauth disabled. This is just to finalize the user side abi as of now
> and KVM can be updated later.
If just flag is passed, I think KVM_ARM_VCPU_INIT should just fail.
Otherwise we risk userspace becoming accidentally reliant on behaviour
that may change in the future.
Cheers
---Dave
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