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Subject[PATCH v2] KVM: x86: allow compiling out the Xen hypercall interface
Date
The Xen hypercall interface adds to the attack surface of the hypervisor
and will be used quite rarely. Allow compiling it out.

Suggested-by: Christoph Hellwig <hch@lst.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
v1->v2: do not use stubs for the ioctls, cull KVM_CAP_XEN_HVM too

arch/x86/kvm/Kconfig | 9 +++++++++
arch/x86/kvm/Makefile | 3 ++-
arch/x86/kvm/x86.c | 8 ++++++++
arch/x86/kvm/xen.h | 24 +++++++++++++++++++++++-
4 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 7ac592664c52..bdda1a386293 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -103,6 +103,15 @@ config KVM_AMD_SEV
Provides support for launching Encrypted VMs (SEV) and Encrypted VMs
with Encrypted State (SEV-ES) on AMD processors.

+config KVM_XEN
+ bool "Support for Xen hypercall interface"
+ depends on KVM && IA32_FEAT_CTL
+ help
+ Provides KVM support for the hosting Xen HVM guests and
+ passing Xen hypercalls to userspace.
+
+ If in doubt, say "N".
+
config KVM_MMU_AUDIT
bool "Audit KVM MMU"
depends on KVM && TRACEPOINTS
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index aeab168c5711..1b4766fe1de2 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -14,11 +14,12 @@ kvm-y += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
$(KVM)/dirty_ring.o
kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o

-kvm-y += x86.o emulate.o i8259.o irq.o lapic.o xen.o \
+kvm-y += x86.o emulate.o i8259.o irq.o lapic.o \
i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \
mmu/spte.o
kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
+kvm-$(CONFIG_KVM_XEN) += xen.o

kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
vmx/evmcs.o vmx/nested.o vmx/posted_intr.o
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bfc928495bd4..4a5ce57b0bb2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3755,11 +3755,13 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
r = 1;
break;
+#ifdef CONFIG_KVM_XEN
case KVM_CAP_XEN_HVM:
r = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
KVM_XEN_HVM_CONFIG_SHARED_INFO;
break;
+#endif
case KVM_CAP_SYNC_REGS:
r = KVM_SYNC_X86_VALID_FIELDS;
break;
@@ -5012,6 +5014,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
case KVM_GET_SUPPORTED_HV_CPUID:
r = kvm_ioctl_get_supported_hv_cpuid(vcpu, argp);
break;
+#ifdef CONFIG_KVM_XEN
case KVM_XEN_VCPU_GET_ATTR: {
struct kvm_xen_vcpu_attr xva;

@@ -5032,6 +5035,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = kvm_xen_vcpu_set_attr(vcpu, &xva);
break;
}
+#endif
default:
r = -EINVAL;
}
@@ -5653,6 +5657,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
kvm->arch.bsp_vcpu_id = arg;
mutex_unlock(&kvm->lock);
break;
+#ifdef CONFIG_KVM_XEN
case KVM_XEN_HVM_CONFIG: {
struct kvm_xen_hvm_config xhc;
r = -EFAULT;
@@ -5681,6 +5686,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
r = kvm_xen_hvm_set_attr(kvm, &xha);
break;
}
+#endif
case KVM_SET_CLOCK: {
struct kvm_clock_data user_ns;
u64 now_ns;
@@ -8039,8 +8045,10 @@ void kvm_arch_exit(void)
kvm_mmu_module_exit();
free_percpu(user_return_msrs);
kmem_cache_destroy(x86_fpu_cache);
+#ifdef CONFIG_KVM_XEN
static_key_deferred_flush(&kvm_xen_enabled);
WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key));
+#endif
}

static int __kvm_vcpu_halt(struct kvm_vcpu *vcpu, int state, int reason)
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index b66a921776f4..87eaf2be9549 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -9,6 +9,7 @@
#ifndef __ARCH_X86_KVM_XEN_H__
#define __ARCH_X86_KVM_XEN_H__

+#ifdef CONFIG_KVM_XEN
#include <linux/jump_label_ratelimit.h>

extern struct static_key_false_deferred kvm_xen_enabled;
@@ -18,7 +19,6 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
-int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data);
int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc);
void kvm_xen_destroy_vm(struct kvm *kvm);
@@ -38,6 +38,28 @@ static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)

return 0;
}
+#else
+static inline int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
+{
+ return 1;
+}
+
+static inline void kvm_xen_destroy_vm(struct kvm *kvm)
+{
+}
+
+static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
+{
+ return false;
+}
+
+static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
+{
+ return 0;
+}
+#endif
+
+int kvm_xen_hypercall(struct kvm_vcpu *vcpu);

/* 32-bit compatibility definitions, also used natively in 32-bit build */
#include <asm/pvclock-abi.h>
--
2.26.2
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