Hi Andrew,
On Mon, 03 Jan 2022 13:46:01 +0000,
Andrew Jones <drjones@xxxxxxxxxx> wrote:
>
> 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).
Sure, works for me. Do we need to keep a trace of the available
options? I'm not sure how a user is supposed to find out about those
(I always end-up grepping through the code base, and something tells
me I'm doing it wrong...). The QMP stuff flies way over my head.
> > 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.
Happy to merge things more, though using qdev_property_add_static()
feels a bit odd here (I have to forcefully replicate the probed state
into the cpu->prop_pauth property in order to have a sensible default
on KVM).
Anyway, I'll post something with this hack, and we add another coat of
paint to the bike shed! ;-)
>
> > +
> > 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.
Yup, works nicely, and allows for some further cleanups.
>
>
> > 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.
Actually, this can go altogether, as it can now be made static in
kvm64.c and not be visible outside of the KVM code at all.
Thanks a lot for the review and the guidance!
M.
--
Without deviation from the norm, progress is not possible.
