[PATCH v5 22/23] arm64: KVM: Allow mapping of vectors outside of the RAM region
Marc Zyngier
marc.zyngier at arm.com
Wed Mar 14 05:02:33 PDT 2018
On 14/03/18 11:40, James Morse wrote:
> Hi Marc,
>
> On 01/03/18 15:55, Marc Zyngier wrote:
>> We're now ready to map our vectors in weird and wonderful locations.
>> On enabling ARM64_HARDEN_EL2_VECTORS, a vector slots gets allocated
>> if this hasn't been already done via ARM64_HARDEN_BRANCH_PREDICTOR
>> and gets mapped outside of the normal RAM region, next to the
>> idmap.
>>
>> That way, being able to obtain VBAR_EL2 doesn't reveal the mapping
>> of the rest of the hypervisor code.
>
>> diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt
>> index c58cc5dbe667..c5dab30d3389 100644
>> --- a/Documentation/arm64/memory.txt
>> +++ b/Documentation/arm64/memory.txt
>> @@ -90,7 +90,8 @@ When using KVM without the Virtualization Host Extensions, the
>> hypervisor maps kernel pages in EL2 at a fixed (and potentially
>> random) offset from the linear mapping. See the kern_hyp_va macro and
>> kvm_update_va_mask function for more details. MMIO devices such as
>> -GICv2 gets mapped next to the HYP idmap page.
>> +GICv2 gets mapped next to the HYP idmap page, as do vectors when
>> +ARM64_HARDEN_EL2_VECTORS is selected for particular CPUs.
>>
>> When using KVM with the Virtualization Host Extensions, no additional
>> mappings are created, since the host kernel runs directly in EL2.
>
>> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
>> index 3da9e5aea936..433d13d0c271 100644
>> --- a/arch/arm64/include/asm/kvm_mmu.h
>> +++ b/arch/arm64/include/asm/kvm_mmu.h
>> @@ -360,33 +360,90 @@ static inline unsigned int kvm_get_vmid_bits(void)
>> return (cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR1_VMIDBITS_SHIFT) == 2) ? 16 : 8;
>> }
>>
>> -#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
>> +#if (defined(CONFIG_HARDEN_BRANCH_PREDICTOR) || \
>> + defined(CONFIG_HARDEN_EL2_VECTORS))
>> +/*
>> + * EL2 vectors can be mapped and rerouted in a number of ways,
>> + * depending on the kernel configuration and CPU present:
>> + *
>> + * - If the CPU has the ARM64_HARDEN_BRANCH_PREDICTOR cap, the
>> + * hardening sequence is placed in one of the vector slots, which is
>> + * executed before jumping to the real vectors.
>> + *
>> + * - If the CPU has both the ARM64_HARDEN_EL2_VECTORS and BP
>> + * hardening, the slot containing the hardening sequence is mapped
>> + * next to the idmap page, and executed before jumping to the real
>> + * vectors.
>> + *
>> + * - If the CPU only has ARM64_HARDEN_EL2_VECTORS, then an empty slot
>> + * is selected, mapped next to the idmap page, and executed before
>> + * jumping to the real vectors.
>
>> + * Note that ARM64_HARDEN_EL2_VECTORS is somewhat incompatible with
>> + * VHE, as we don't have hypervisor-specific mappings. If the system
>> + * is VHE and yet selects this capability, it will be ignored.
>
> Silently? This isn't a problem as the CPUs you enable this for don't have VHE.
> Is it worth a warning? If we did ever need to support it, we can pull the same
> trick the arch code uses, using a fixmap entry for the vectors.
I guess I can put a WARN_ONCE() there, wouldn't hurt. The fixmap approach would work, but it is just complicated on heterogeneous systems, as you'd have to have one fixmap entry per CPU type. I'm not looking forward to implementing this!
>
>
>> + */
>> #include <asm/mmu.h>
>>
>> +extern void *__kvm_bp_vect_base;
>> +extern int __kvm_harden_el2_vector_slot;
>> +
>> static inline void *kvm_get_hyp_vector(void)
>> {
>> struct bp_hardening_data *data = arm64_get_bp_hardening_data();
>> - void *vect = kvm_ksym_ref(__kvm_hyp_vector);
>> + int slot = -1;
>> +
>> + if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR) && data->fn)
>> + slot = data->hyp_vectors_slot;
>> +
>> + if (cpus_have_const_cap(ARM64_HARDEN_EL2_VECTORS) &&
>> + !has_vhe() && slot == -1)
>> + slot = __kvm_harden_el2_vector_slot;
>>
>> - if (data->fn) {
>> - vect = __bp_harden_hyp_vecs_start +
>> - data->hyp_vectors_slot * SZ_2K;
>> + if (slot != -1) {
>> + void *vect;
>>
>> if (!has_vhe())
>> - vect = lm_alias(vect);
>> + vect = __kvm_bp_vect_base;
>> + else
>> + vect = __bp_harden_hyp_vecs_start;
>> + vect += slot * SZ_2K;
>> +
>> + return vect;
>> }
>>
>> - vect = kern_hyp_va(vect);
>> - return vect;
>> + return kern_hyp_va(kvm_ksym_ref(__kvm_hyp_vector));
>> }
>>
>> +/* This is only called on a !VHE system */
>> static inline int kvm_map_vectors(void)
>> {
>> - return create_hyp_mappings(kvm_ksym_ref(__bp_harden_hyp_vecs_start),
>> - kvm_ksym_ref(__bp_harden_hyp_vecs_end),
>> - PAGE_HYP_EXEC);
>> -}
>> + phys_addr_t vect_pa = virt_to_phys(__bp_harden_hyp_vecs_start);
>> + unsigned long size = __bp_harden_hyp_vecs_end - __bp_harden_hyp_vecs_start;
>> +
>> + if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR)) {
>> + int ret;
>> +
>> + ret = create_hyp_mappings(kvm_ksym_ref(__bp_harden_hyp_vecs_start),
>> + kvm_ksym_ref(__bp_harden_hyp_vecs_end),
>> + PAGE_HYP_EXEC);
>
> We don't have to do this for the regular vectors, as they are part of the
> __hyp_text. How come these aren't?
I guess that was an oversight in the Spectre patches, which lives on. I'll have a look at simplifying this.
>
> The existing Makefile depends on KVM to build these. How come it isn't under
> arch/arm64/kvm?
It wasn't clear from the outset that this file would turn into something
that is strictly KVM related. I could move it, but I'm not sure that'd
make things simpler.
>
>
>> + if (ret)
>> + return ret;
>> +
>> + __kvm_bp_vect_base = kvm_ksym_ref(__bp_harden_hyp_vecs_start);
>> + __kvm_bp_vect_base = kern_hyp_va(__kvm_bp_vect_base);
>> + }
>> +
>> + if (cpus_have_const_cap(ARM64_HARDEN_EL2_VECTORS)) {
>> + __kvm_harden_el2_vector_slot = atomic_inc_return(&arm64_el2_vector_last_slot);
>> + BUG_ON(__kvm_harden_el2_vector_slot >= BP_HARDEN_EL2_SLOTS);
>> + return create_hyp_exec_mappings(vect_pa, size,
>> + &__kvm_bp_vect_base);
>> + }
>>
>> + return 0;
>> +}
>> #else
>> static inline void *kvm_get_hyp_vector(void)
>> {
>
>> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
>> index b87541360f43..e7fc471c91a6 100644
>> --- a/arch/arm64/kernel/Makefile
>> +++ b/arch/arm64/kernel/Makefile
>> @@ -54,8 +54,8 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
>> arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
>> arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
>>
>> -ifeq ($(CONFIG_KVM),y)
>> -arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR) += bpi.o
>> +ifneq ($(filter y,$(CONFIG_HARDEN_BRANCH_PREDICTOR) $(CONFIG_HARDEN_EL2_VECTORS)),)
>> +arm64-obj-$(CONFIG_KVM) += bpi.o
>> endif
>
> Isn't Kconfig 'select'ing a hidden-option the usual way this is done?
Something like this?
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index e7fc471c91a6..93bce17109a6 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -54,9 +54,7 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
-ifneq ($(filter y,$(CONFIG_HARDEN_BRANCH_PREDICTOR) $(CONFIG_HARDEN_EL2_VECTORS)),)
-arm64-obj-$(CONFIG_KVM) += bpi.o
-endif
+arm64-obj-$(CONFIG_KVM_INDIRECT_VECTORS)+= bpi.o
obj-y += $(arm64-obj-y) vdso/ probes/
obj-m += $(arm64-obj-m)
diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 2257dfcc44cc..a2e3a5af1113 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig
@@ -57,6 +57,9 @@ config KVM_ARM_PMU
Adds support for a virtual Performance Monitoring Unit (PMU) in
virtual machines.
+config KVM_INDIRECT_VECTORS
+ def_bool KVM && (HARDEN_BRANCH_PREDICTOR || HARDEN_EL2_VECTORS)
+
source drivers/vhost/Kconfig
endif # VIRTUALIZATION
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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