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

[Amit Daniel Kachhap <amit.kachhap@arm.com>]

Hi,

On 4/16/19 10:02 PM, Dave Martin wrote:
> 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@arm.com>
>> ---
>> 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 ()
ok.
> 
>> +		(kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> 
> Funny indentation?
ok will align it.
> 
>> +		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
May be 1 more check can be added here like,

if (kvm->cfg.arch.enable_ptrauth && kvm->cfg.arch.disable_ptrauth) {
	print_err("Only 1 option should be supplied\n");
	ret -EINVAL;
}

> --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.

Since now ptrauth is enabled by default if system supports it even 
though it is not explicitly requested. so I thought --enable-ptrauth
option has to now forcefully enable ptrauth and may cause some error 
message in failure.
Did I interpret something different from your last suggestion[1]?

Actually we can skip with --enable-ptrauth and have just 2 option,
* By default enable ptrauth if system supports it.
* --disable-ptrauth: useful to migrate non-ptrauth guests on ptrauth hosts

[1]:https://lkml.org/lkml/2019/4/5/171

Thanks,
Amit Daniel
> 
> 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
>