Re: [kvmtool PATCH v8 9/9] KVM: arm/arm64: Add a vcpu feature for pointer authentication

From: Amit Daniel Kachhap <amit.kachhap@arm.com>
To: Dave Martin <Dave.Martin@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Kristina Martsenko <kristina.martsenko@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [kvmtool PATCH v8 9/9] KVM: arm/arm64: Add a vcpu feature for pointer authentication
Date: Mon, 8 Apr 2019 14:13:23 +0530	[thread overview]
Message-ID: <d0306ab8-7d65-85d2-a4b5-2579f7efea69@arm.com> (raw)
In-Reply-To: <20190405110423.GV3567@e103592.cambridge.arm.com>

Hi Dave,

On 4/5/19 4:34 PM, Dave Martin wrote:
> On Tue, Apr 02, 2019 at 07:57:17AM +0530, Amit Daniel Kachhap wrote:
>> This is 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.
>>
>> A command line option --ptrauth is also required to select this feature.
>>
>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
>> ---
>>
>> Changes since v7:
>> * Added check for capability KVM_CAP_ARM_PTRAUTH_GENERIC
>>
>>   arm/aarch32/include/kvm/kvm-cpu-arch.h    | 1 +
>>   arm/aarch64/include/asm/kvm.h             | 2 ++
>>   arm/aarch64/include/kvm/kvm-config-arch.h | 4 +++-
>>   arm/aarch64/include/kvm/kvm-cpu-arch.h    | 2 ++
>>   arm/include/arm-common/kvm-config-arch.h  | 1 +
>>   arm/kvm-cpu.c                             | 7 +++++++
>>   include/linux/kvm.h                       | 2 ++
>>   7 files changed, 18 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..d4d0d8c 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	4 /* CPU uses address pointer authentication */
>> +#define KVM_ARM_VCPU_PTRAUTH_GENERIC	5 /* 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..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"),
> 
> This should probably say "pointer", not "address" now, since we enable
> both kinds of ptrauth together.  (Sorry!)
yes.
> 
> When discussing how to control SVE, I was eventually convinced that it
> is more user-friendly to make SVE default to on if present, and maybe
> provide two options --disable-sve, --enable-sve, in case the user wants
> to force it off or on instead of just getting what the host supports.
> 
> Passing --enable-sve on a host that doesn't support SVE would then lead
> to kvmtool bailing out with an error, which is probably better then
> silently turning it off.
I agree that leaving the ptrauth as default on makes more sense as it is 
easy for userspace to invoke the kvmtool without adding any extra 
parameter. However all the current 4 vcpu features have a configuration 
option to turn them on except power off.

I suppose for --enable-sve, failure will happen at capability check 
ioctl rather than KVM_ARM_VCPU_INIT.
> 
> I don't have this change in my kvmtool patches yet.
> 
> What's your view?  It makes sense to do things the same way for all
> features if we can.
yes it is sensible to have same tuning options for all new features.
> 
>>   #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..5badcbd 100644
>> --- a/arm/include/arm-common/kvm-config-arch.h
>> +++ b/arm/include/arm-common/kvm-config-arch.h
>> @@ -10,6 +10,7 @@ struct kvm_config_arch {
>>   	bool		aarch32_guest;
>>   	bool		has_pmuv3;
>>   	u64		kaslr_seed;
>> +	bool		has_ptrauth;
>>   	enum irqchip_type irqchip;
>>   	u64		fw_addr;
>>   };
>> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
>> index 7780251..398c9d6 100644
>> --- a/arm/kvm-cpu.c
>> +++ b/arm/kvm-cpu.c
>> @@ -68,6 +68,13 @@ 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);
>>   	}
>>   
>> +	/* Set KVM_ARM_VCPU_PTRAUTH_[ADDRESS/GENERIC] if available */
>> +	if (kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
>> +		kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC)) {
>> +		if (kvm->cfg.arch.has_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
>> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
>> index 6d4ea4b..500ac2b 100644
>> --- a/include/linux/kvm.h
>> +++ b/include/linux/kvm.h
>> @@ -988,6 +988,8 @@ struct kvm_ppc_resize_hpt {
>>   #define KVM_CAP_ARM_VM_IPA_SIZE 165
>>   #define KVM_CAP_MANUAL_DIRTY_LOG_PROTECT 166
>>   #define KVM_CAP_HYPERV_CPUID 167
>> +#define KVM_CAP_ARM_PTRAUTH_ADDRESS 168
>> +#define KVM_CAP_ARM_PTRAUTH_GENERIC 169
> 
> (Note, 168 will probably be KVM_CAP_ARM_SVE, now that the SVE patches
> are in kvmarm/next.)
ok thanks for the information.

Thanks,
Amit Daniel
> 
> Cheers
> ---Dave
> 