KVM: arm64: Use a maple tree to represent the SMCCC filter

Maple tree is an efficient B-tree implementation that is intended for
storing non-overlapping intervals. Such a data structure is a good fit
for the SMCCC filter as it is desirable to sparsely allocate the 32 bit
function ID space.

To that end, add a maple tree to kvm_arch and correctly init/teardown
along with the VM. Wire in a test against the hypercall filter for HVCs
which does nothing until the controls are exposed to userspace.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230404154050.2270077-8-oliver.upton@linux.dev

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index d091d1c..2682b3f 100644 (file)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -16,6 +16,7 @@
 #include <linux/types.h>
 #include <linux/jump_label.h>
 #include <linux/kvm_types.h>
+#include <linux/maple_tree.h>
 #include <linux/percpu.h>
 #include <linux/psci.h>
 #include <asm/arch_gicv3.h>
@@ -221,7 +222,8 @@ struct kvm_arch {
 #define KVM_ARCH_FLAG_EL1_32BIT                                4
        /* PSCI SYSTEM_SUSPEND enabled for the guest */
 #define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED           5
-
+       /* SMCCC filter initialized for the VM */
+#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED          6
        unsigned long flags;
 
        /*
@@ -242,6 +244,7 @@ struct kvm_arch {
 
        /* Hypercall features firmware registers' descriptor */
        struct kvm_smccc_features smccc_feat;
+       struct maple_tree smccc_filter;
 
        /*
         * For an untrusted host VM, 'pkvm.handle' is used to lookup

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index b6e26c0..1202ac0 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -192,6 +192,8 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
        kvm_destroy_vcpus(kvm);
 
        kvm_unshare_hyp(kvm, kvm + 1);
+
+       kvm_arm_teardown_hypercalls(kvm);
 }
 
 int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)

diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 0be974e..ba7cd84 100644 (file)
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -121,8 +121,58 @@ static bool kvm_smccc_test_fw_bmap(struct kvm_vcpu *vcpu, u32 func_id)
        }
 }
 
+#define SMCCC_ARCH_RANGE_BEGIN ARM_SMCCC_VERSION_FUNC_ID
+#define SMCCC_ARCH_RANGE_END                           \
+       ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,         \
+                          ARM_SMCCC_SMC_32,            \
+                          0, ARM_SMCCC_FUNC_MASK)
+
+static void init_smccc_filter(struct kvm *kvm)
+{
+       int r;
+
+       mt_init(&kvm->arch.smccc_filter);
+
+       /*
+        * Prevent userspace from handling any SMCCC calls in the architecture
+        * range, avoiding the risk of misrepresenting Spectre mitigation status
+        * to the guest.
+        */
+       r = mtree_insert_range(&kvm->arch.smccc_filter,
+                              SMCCC_ARCH_RANGE_BEGIN, SMCCC_ARCH_RANGE_END,
+                              xa_mk_value(KVM_SMCCC_FILTER_HANDLE),
+                              GFP_KERNEL_ACCOUNT);
+       WARN_ON_ONCE(r);
+}
+
+static u8 kvm_smccc_filter_get_action(struct kvm *kvm, u32 func_id)
+{
+       unsigned long idx = func_id;
+       void *val;
+
+       if (!test_bit(KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags))
+               return KVM_SMCCC_FILTER_HANDLE;
+
+       /*
+        * But where's the error handling, you say?
+        *
+        * mt_find() returns NULL if no entry was found, which just so happens
+        * to match KVM_SMCCC_FILTER_HANDLE.
+        */
+       val = mt_find(&kvm->arch.smccc_filter, &idx, idx);
+       return xa_to_value(val);
+}
+
 static u8 kvm_smccc_get_action(struct kvm_vcpu *vcpu, u32 func_id)
 {
+       /*
+        * Intervening actions in the SMCCC filter take precedence over the
+        * pseudo-firmware register bitmaps.
+        */
+       u8 action = kvm_smccc_filter_get_action(vcpu->kvm, func_id);
+       if (action != KVM_SMCCC_FILTER_HANDLE)
+               return action;
+
        if (kvm_smccc_test_fw_bmap(vcpu, func_id) ||
            kvm_smccc_default_allowed(func_id))
                return KVM_SMCCC_FILTER_HANDLE;
@@ -263,6 +313,13 @@ void kvm_arm_init_hypercalls(struct kvm *kvm)
        smccc_feat->std_bmap = KVM_ARM_SMCCC_STD_FEATURES;
        smccc_feat->std_hyp_bmap = KVM_ARM_SMCCC_STD_HYP_FEATURES;
        smccc_feat->vendor_hyp_bmap = KVM_ARM_SMCCC_VENDOR_HYP_FEATURES;
+
+       init_smccc_filter(kvm);
+}
+
+void kvm_arm_teardown_hypercalls(struct kvm *kvm)
+{
+       mtree_destroy(&kvm->arch.smccc_filter);
 }
 
 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)

diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
index 8f4e33b..fe6c315 100644 (file)
--- a/include/kvm/arm_hypercalls.h
+++ b/include/kvm/arm_hypercalls.h
@@ -43,6 +43,7 @@ static inline void smccc_set_retval(struct kvm_vcpu *vcpu,
 struct kvm_one_reg;
 
 void kvm_arm_init_hypercalls(struct kvm *kvm);
+void kvm_arm_teardown_hypercalls(struct kvm *kvm);
 int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu);
 int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices);
 int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);