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Date: Wed, 24 Apr 2019 12:32:22 +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 v10 5/5] KVM: arm/arm64: Add a vcpu feature for
pointer authentication
Hi,
On 4/23/19 9:16 PM, Dave Martin wrote:
> On Tue, Apr 23, 2019 at 10:12:38AM +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@....com>
>> ---
>>
>> Changes since v9:
>> * Added a error check for both enable-ptrauth and disable-ptrauth
>> option.
>> * Make the error explicit when enable-ptrauth is provided [Dave Martin].
>>
>> 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 | 20 ++++++++++++++++++--
>> include/linux/kvm.h | 2 ++
>> 7 files changed, 32 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..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..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");
>
> Preferably, print the leading dashes, the same as the user would see
> on the command line (e.g., --enable-ptrauth, --disable-ptrauth).
>
> For brevity, we could write something like:
>
> die("--enable-ptrauth conflicts with --disable-ptrauth");
>
>> + /*
>> + * 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");
>
> We don't special-case this error message for any other feature yet:
> there are a variety of reasons why we might have failed, so suggesting
> that the failure is something to do with ptrauth may be misleading to
> the user.
>
> If we want to be more informative, we could do something like the
> following:
>
> bool supported;
>
> supported = kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC);
>
> if (kvm->cfg.arch.enable_ptrauth && !supported)
> die("--enable-ptrauth not supported on this host");
>
> if (supported && !kvm->cfg.arch.disable_ptrauth)
> vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
>
> /* ... */
>
> if (err || target->init(vcpu))
> die("Unable to initialise vcpu");
>
> We don't do this for any other feature today, but since it helps the
> user to understand what went wrong it's probably a good idea.
Yes this is more clear. As Mark has picked the core guest ptrauth
patches. I will post this changes as standalone.
Thanks,
Amit Daniel
>
> [...]
>
> Cheers
> ---Dave
>
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