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Date: Wed, 24 Apr 2019 14:41:21 +0100
From: Dave Martin <Dave.Martin@....com>
To: Amit Daniel Kachhap <amit.kachhap@....com>
Cc: Marc Zyngier <marc.zyngier@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
linux-kernel@...r.kernel.org,
Kristina Martsenko <kristina.martsenko@....com>,
Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [kvmtool PATCH v10 5/5] KVM: arm/arm64: Add a vcpu feature for
pointer authentication
On Wed, Apr 24, 2019 at 12:32:22PM +0530, Amit Daniel Kachhap wrote:
> 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.
Sounds good. (I also need to do that separately for SVE...)
Cheers
---Dave
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