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Date: Wed, 17 Apr 2019 18:06:11 +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 v9 5/5] KVM: arm/arm64: Add a vcpu feature for
pointer authentication
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@....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
>
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