Re: [PATCH kvmtool v3 5/9] KVM: arm/arm64: Add a vcpu feature for pointer authentication

Andre Przywara
2019-05-31T17:04:30Z

On Thu, 30 May 2019 16:13:10 +0100
Dave Martin <Dave.Martin@arm.com> wrote:

> From: Amit Daniel Kachhap <amit.kachhap@arm.com>
>
> This patch adds a runtime capabality for KVM tool to enable Arm64 8.3
> Pointer Authentication in guest kernel. Two vcpu features
> KVM_ARM_VCPU_PTRAUTH_[ADDRESS/GENERIC] are supplied together to enable
> Pointer Authentication in KVM guest after checking the capability.
>
> Command line options --enable-ptrauth and --disable-ptrauth are added
> to use this feature. However, if those options are not provided then
> also this feature is enabled if host supports this capability.

I don't really get the purpose of two options, I think that's quite confusing. Should the first one either be dropped at all or called something with "force"?
I guess the idea is to fail if pointer auth isn't available, but the option is supplied?

Or maybe have one option with parameters?
--ptrauth[,=enable,=disable]

> The macros defined in the headers are not in sync and should be replaced
> from the upstream.

This is no longer true, I guess?

Cheers,
Andre.

> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com> [merge new kernel heaers]
> ---
> arm/aarch32/include/kvm/kvm-cpu-arch.h | 2 ++
> arm/aarch64/include/kvm/kvm-config-arch.h | 6 +++++-
> arm/aarch64/include/kvm/kvm-cpu-arch.h | 3 +++
> arm/include/arm-common/kvm-config-arch.h | 2 ++
> arm/kvm-cpu.c | 20 ++++++++++++++++++--
> 5 files changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/arm/aarch32/include/kvm/kvm-cpu-arch.h b/arm/aarch32/include/kvm/kvm-cpu-arch.h
> index d28ea67..3ec6f03 100644
> --- a/arm/aarch32/include/kvm/kvm-cpu-arch.h
> +++ b/arm/aarch32/include/kvm/kvm-cpu-arch.h
> @@ -13,4 +13,6 @@
> #define ARM_CPU_ID 0, 0, 0
> #define ARM_CPU_ID_MPIDR 5
>
> +#define ARM_VCPU_PTRAUTH_FEATURE 0
> +
> #endif /* KVM__KVM_CPU_ARCH_H */
> diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
> index 04be43d..0279b13 100644
> --- a/arm/aarch64/include/kvm/kvm-config-arch.h
> +++ b/arm/aarch64/include/kvm/kvm-config-arch.h
> @@ -8,7 +8,11 @@
> "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', "enable-ptrauth", &(cfg)->enable_ptrauth, \
> + "Enables pointer authentication"), \
> + OPT_BOOLEAN('\0', "disable-ptrauth", &(cfg)->disable_ptrauth, \
> + "Disables pointer authentication"),
>
> #include "arm-common/kvm-config-arch.h"
>
> diff --git a/arm/aarch64/include/kvm/kvm-cpu-arch.h b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> index a9d8563..9fa99fb 100644
> --- a/arm/aarch64/include/kvm/kvm-cpu-arch.h
> +++ b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> @@ -17,4 +17,7 @@
> #define ARM_CPU_CTRL 3, 0, 1, 0
> #define ARM_CPU_CTRL_SCTLR_EL1 0
>
> +#define ARM_VCPU_PTRAUTH_FEATURE ((1UL << KVM_ARM_VCPU_PTRAUTH_ADDRESS) \
> + | (1UL << KVM_ARM_VCPU_PTRAUTH_GENERIC))
> +
> #endif /* KVM__KVM_CPU_ARCH_H */
> diff --git a/arm/include/arm-common/kvm-config-arch.h b/arm/include/arm-common/kvm-config-arch.h
> index 5734c46..1b4287d 100644
> --- a/arm/include/arm-common/kvm-config-arch.h
> +++ b/arm/include/arm-common/kvm-config-arch.h
> @@ -10,6 +10,8 @@ struct kvm_config_arch {
> bool aarch32_guest;
> bool has_pmuv3;
> u64 kaslr_seed;
> + bool enable_ptrauth;
> + bool disable_ptrauth;
> enum irqchip_type irqchip;
> u64 fw_addr;
> };
> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
> index 7780251..acd1d5f 100644
> --- a/arm/kvm-cpu.c
> +++ b/arm/kvm-cpu.c
> @@ -68,6 +68,18 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
> vcpu_init.features[0] |= (1UL << KVM_ARM_VCPU_PSCI_0_2);
> }
>
> + /* Check Pointer Authentication command line arguments. */
> + if (kvm->cfg.arch.enable_ptrauth && kvm->cfg.arch.disable_ptrauth)
> + die("Both enable-ptrauth and disable-ptrauth option cannot be present");
> + /*
> + * Always enable Pointer Authentication if system supports
> + * this extension unless disable-ptrauth option is present.
> + */
> + if (kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> + kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC) &&
> + !kvm->cfg.arch.disable_ptrauth)
> + vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
> +
> /*
> * If the preferred target ioctl is successful then
> * use preferred target else try each and every target type
> @@ -106,8 +118,12 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
> die("Unable to find matching target");
> }
>
> - if (err || target->init(vcpu))
> - die("Unable to initialise vcpu");
> + if (err || target->init(vcpu)) {
> + if (kvm->cfg.arch.enable_ptrauth)
> + die("Unable to initialise vcpu with pointer authentication feature");
> + else
> + die("Unable to initialise vcpu");
> + }
>
> coalesced_offset = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION,
> KVM_CAP_COALESCED_MMIO);