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Date: Mon, 8 Apr 2019 14:13:23 +0530
From: Amit Daniel Kachhap <amit.kachhap@....com>
To: Dave Martin <Dave.Martin@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
Marc Zyngier <marc.zyngier@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Kristina Martsenko <kristina.martsenko@....com>,
kvmarm@...ts.cs.columbia.edu,
Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
linux-kernel@...r.kernel.org
Subject: Re: [kvmtool PATCH v8 9/9] KVM: arm/arm64: Add a vcpu feature for
pointer authentication
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@....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
>
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