Re: [kvmtool PATCH v9 5/5] KVM: arm/arm64: Add a vcpu feature for pointer authentication

[Dave Martin]

On Fri, Apr 12, 2019 at 08:50:36AM +0530, Amit Daniel Kachhap wrote:
> 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.
> 
> The macros defined in the headers are not in sync and should be replaced
> from the upstream.
> 
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
> ---
> Changes since v8:
> *  Added option --enable-ptrauth and --disable-ptrauth to use ptrauth. Also
>    enable ptrauth if no option provided and Host supports ptrauth. [Dave Martin]
> * The macro definition are not linear as the kvmtool is not synchronised with the
>   kernel changes present in kvmarm/next tree.
> 
>  arm/aarch32/include/kvm/kvm-cpu-arch.h    |  1 +
>  arm/aarch64/include/asm/kvm.h             |  2 ++
>  arm/aarch64/include/kvm/kvm-config-arch.h |  6 +++++-
>  arm/aarch64/include/kvm/kvm-cpu-arch.h    |  2 ++
>  arm/include/arm-common/kvm-config-arch.h  |  2 ++
>  arm/kvm-cpu.c                             | 11 +++++++++++
>  include/linux/kvm.h                       |  2 ++
>  7 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/arm/aarch32/include/kvm/kvm-cpu-arch.h b/arm/aarch32/include/kvm/kvm-cpu-arch.h
> index d28ea67..520ea76 100644
> --- a/arm/aarch32/include/kvm/kvm-cpu-arch.h
> +++ b/arm/aarch32/include/kvm/kvm-cpu-arch.h
> @@ -13,4 +13,5 @@
>  #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/asm/kvm.h b/arm/aarch64/include/asm/kvm.h
> index 97c3478..a2546e6 100644
> --- a/arm/aarch64/include/asm/kvm.h
> +++ b/arm/aarch64/include/asm/kvm.h
> @@ -102,6 +102,8 @@ struct kvm_regs {
>  #define KVM_ARM_VCPU_EL1_32BIT		1 /* CPU running a 32bit VM */
>  #define KVM_ARM_VCPU_PSCI_0_2		2 /* CPU uses PSCI v0.2 */
>  #define KVM_ARM_VCPU_PMU_V3		3 /* Support guest PMUv3 */
> +#define KVM_ARM_VCPU_PTRAUTH_ADDRESS	5 /* CPU uses address pointer authentication */
> +#define KVM_ARM_VCPU_PTRAUTH_GENERIC	6 /* CPU uses generic pointer authentication */
>  
>  struct kvm_vcpu_init {
>  	__u32 target;
> 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..fcc2107 100644
> --- a/arm/aarch64/include/kvm/kvm-cpu-arch.h
> +++ b/arm/aarch64/include/kvm/kvm-cpu-arch.h
> @@ -17,4 +17,6 @@
>  #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..a45a649 100644
> --- a/arm/kvm-cpu.c
> +++ b/arm/kvm-cpu.c
> @@ -69,6 +69,17 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>  	}
>  
>  	/*
> +	 * Always enable Pointer Authentication if requested. If system supports
> +	 * this extension then also enable it by default provided no disable
> +	 * request present.
> +	 */
> +	if ((kvm->cfg.arch.enable_ptrauth) ||

Nit: redundant ()

> +		(kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&

Funny indentation?

> +		kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC) &&
> +		!kvm->cfg.arch.disable_ptrauth))
> +			vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
> +

Hmm, we have some weird behaviours here: --enable-ptrauth
--disable-ptrauth will result in us trying to enable it, and
--enable-ptrauth without the required caps will result in an unhelpful
"Unable to initialise vcpu" error message.  I'm not sure this is a
whole lot worse than the way other options behave today, though.

You could try to be more explicit about what happens in these cases, but
I'm not sure it's worth it given the state of the existing code.

[...]

Cheers
---Dave