Hi Marc,
On Tue, Dec 28, 2021 at 06:23:47PM +0000, Marc Zyngier wrote:
> Add basic support for Pointer Authentication when running a KVM
> guest and that the host supports it, loosely based on the SVE
> support.
>
> Although the feature is enabled by default when the host advertises
> it, it is possible to disable it by setting the 'pauth=off' CPU
> property.
>
> Tested on an Apple M1 running 5.16-rc6.
>
> Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> Cc: Andrew Jones <drjones@xxxxxxxxxx>
> Cc: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Cc: Peter Maydell <peter.maydell@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> docs/system/arm/cpu-features.rst | 5 +++++
> target/arm/cpu.c | 1 +
> target/arm/cpu.h | 1 +
> target/arm/cpu64.c | 36 ++++++++++++++++++++++++++++++++
> target/arm/kvm.c | 13 ++++++++++++
> target/arm/kvm64.c | 10 +++++++++
> target/arm/kvm_arm.h | 7 +++++++
> 7 files changed, 73 insertions(+)
>
> diff --git a/docs/system/arm/cpu-features.rst b/docs/system/arm/cpu-features.rst
> index 584eb17097..c9e39546a5 100644
> --- a/docs/system/arm/cpu-features.rst
> +++ b/docs/system/arm/cpu-features.rst
> @@ -211,6 +211,11 @@ the list of KVM VCPU features and their descriptions.
> influence the guest scheduler behavior and/or be
> exposed to the guest userspace.
>
> + pauth Enable or disable ``FEAT_Pauth``, pointer
> + authentication. By default, the feature is enabled
> + with ``-cpu host`` if supported by both the host
> + kernel and the hardware.
> +
Thanks for considering a documentation update. In this case, though, I
think we should delete the "TCG VCPU Features" pauth paragraph, rather
than add a new "KVM VCPU Features" pauth paragraph. We don't need to
document each CPU feature. We just document complex ones, like sve*,
KVM specific ones (kvm-*), and TCG specific ones (now only pauth-impdef).
> TCG VCPU Features
> =================
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index a211804fd3..68b09cbc6a 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -2091,6 +2091,7 @@ static void arm_host_initfn(Object *obj)
> kvm_arm_set_cpu_features_from_host(cpu);
> if (arm_feature(&cpu->env, ARM_FEATURE_AARCH64)) {
> aarch64_add_sve_properties(obj);
> + aarch64_add_pauth_properties(obj);
> }
> #else
> hvf_arm_set_cpu_features_from_host(cpu);
> diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> index e33f37b70a..c6a4d50e82 100644
> --- a/target/arm/cpu.h
> +++ b/target/arm/cpu.h
> @@ -1076,6 +1076,7 @@ void aarch64_sve_narrow_vq(CPUARMState *env, unsigned vq);
> void aarch64_sve_change_el(CPUARMState *env, int old_el,
> int new_el, bool el0_a64);
> void aarch64_add_sve_properties(Object *obj);
> +void aarch64_add_pauth_properties(Object *obj);
>
> /*
> * SVE registers are encoded in KVM's memory in an endianness-invariant format.
> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> index 15245a60a8..305c0e19fe 100644
> --- a/target/arm/cpu64.c
> +++ b/target/arm/cpu64.c
> @@ -625,6 +625,42 @@ void aarch64_add_sve_properties(Object *obj)
> #endif
> }
>
> +static bool cpu_arm_get_pauth(Object *obj, Error **errp)
> +{
> + ARMCPU *cpu = ARM_CPU(obj);
> + return cpu_isar_feature(aa64_pauth, cpu);
> +}
> +
> +static void cpu_arm_set_pauth(Object *obj, bool value, Error **errp)
> +{
> + ARMCPU *cpu = ARM_CPU(obj);
> + uint64_t t;
> +
> + if (value) {
> + if (!kvm_arm_pauth_supported()) {
> + error_setg(errp, "'pauth' feature not supported by KVM on this host");
> + }
> +
> + return;
> + }
> +
> + /*
> + * If the host supports PAuth, we only end-up here if the user has
> + * disabled the support, and value is false.
> + */
> + t = cpu->isar.id_aa64isar1;
> + t = FIELD_DP64(t, ID_AA64ISAR1, APA, value);
> + t = FIELD_DP64(t, ID_AA64ISAR1, GPA, value);
> + t = FIELD_DP64(t, ID_AA64ISAR1, API, value);
> + t = FIELD_DP64(t, ID_AA64ISAR1, GPI, value);
> + cpu->isar.id_aa64isar1 = t;
> +}
> +
> +void aarch64_add_pauth_properties(Object *obj)
> +{
> + object_property_add_bool(obj, "pauth", cpu_arm_get_pauth, cpu_arm_set_pauth);
> +}
I think we should try to merge as much as possible between the TCG and KVM
pauth property handling. I think we just need to move the
qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_property) call into
KVM/TCG common code and then modify arm_cpu_pauth_finalize() to
handle checking KVM for support when KVM is enabled and also to not
look at the impdef property.
> +
> void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp)
> {
> int arch_val = 0, impdef_val = 0;
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index bbf1ce7ba3..71e2f46ce8 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -84,6 +84,7 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
> if (vmfd < 0) {
> goto err;
> }
> +
> cpufd = ioctl(vmfd, KVM_CREATE_VCPU, 0);
> if (cpufd < 0) {
> goto err;
> @@ -94,6 +95,18 @@ bool kvm_arm_create_scratch_host_vcpu(const uint32_t *cpus_to_try,
> goto finish;
> }
>
> + /*
> + * Ask for Pointer Authentication if supported. We can't play the
> + * SVE trick of synthetising the ID reg as KVM won't tell us
> + * whether we have the architected or IMPDEF version of PAuth, so
> + * we have to use the actual ID regs.
> + */
> + if (ioctl(vmfd, KVM_CHECK_EXTENSION, KVM_CAP_ARM_PTRAUTH_ADDRESS) > 0 &&
> + ioctl(vmfd, KVM_CHECK_EXTENSION, KVM_CAP_ARM_PTRAUTH_GENERIC) > 0) {
> + init->features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
> + 1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
> + }
> +
I think kvm_init() is called prior to kvm_arm_get_host_cpu_features(),
which means we can do this instead
diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index e790d6c9a573..d1512035ac5b 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -521,6 +521,17 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
*/
struct kvm_vcpu_init init = { .target = -1, };
+ /*
+ * Ask for Pointer Authentication if supported. We can't play the
+ * SVE trick of synthetising the ID reg as KVM won't tell us
+ * whether we have the architected or IMPDEF version of PAuth, so
+ * we have to use the actual ID regs.
+ */
+ if (kvm_arm_pauth_supported()) {
+ init->features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
+ 1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
+ }
+
if (!kvm_arm_create_scratch_host_vcpu(cpus_to_try, fdarray, &init)) {
return false;
}
Assuming I'm right about the call order, then I think I'd like that more.
> if (init->target == -1) {
> struct kvm_vcpu_init preferred;
>
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index e790d6c9a5..95b6902ca0 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -725,6 +725,12 @@ bool kvm_arm_sve_supported(void)
> return kvm_check_extension(kvm_state, KVM_CAP_ARM_SVE);
> }
>
> +bool kvm_arm_pauth_supported(void)
> +{
> + return (kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
> + kvm_check_extension(kvm_state, KVM_CAP_ARM_PTRAUTH_GENERIC));
> +}
> +
> bool kvm_arm_steal_time_supported(void)
> {
> return kvm_check_extension(kvm_state, KVM_CAP_STEAL_TIME);
> @@ -865,6 +871,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
> assert(kvm_arm_sve_supported());
> cpu->kvm_init_features[0] |= 1 << KVM_ARM_VCPU_SVE;
> }
> + if (cpu_isar_feature(aa64_pauth, cpu)) {
> + cpu->kvm_init_features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
> + 1 << KVM_ARM_VCPU_PTRAUTH_GENERIC);
> + }
>
> /* Do KVM_ARM_VCPU_INIT ioctl */
> ret = kvm_arm_vcpu_init(cs);
> diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> index b7f78b5215..c26acf7866 100644
> --- a/target/arm/kvm_arm.h
> +++ b/target/arm/kvm_arm.h
> @@ -306,6 +306,13 @@ bool kvm_arm_pmu_supported(void);
> */
> bool kvm_arm_sve_supported(void);
>
> +/**
> + * kvm_arm_pauth_supported:
> + *
> + * Returns true if KVM can enable Pointer Authentication and false otherwise.
> + */
> +bool kvm_arm_pauth_supported(void);
> +
If we merge more of the pauth property handling with the TCG code, then
we'll also need a stub in the !CONFIG_KVM section for compiling without
kvm support.
> /**
> * kvm_arm_get_max_vm_ipa_size:
> * @ms: Machine state handle
> --
> 2.30.2
>
Thanks,
drew
