arm64: KVM: Allow mapping of vectors outside of the RAM region

We're now ready to map our vectors in weird and wonderful locations.
On enabling ARM64_HARDEN_EL2_VECTORS, a vector slot 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.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 69 insertions, 9 deletions

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index eb04437d50fa..082110993647 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -360,31 +360,91 @@ 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
+#ifdef CONFIG_KVM_INDIRECT_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 cap and the
+ *   ARM64_HARDEN_BRANCH_PREDICTOR cap, 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 the ARM64_HARDEN_EL2_VECTORS cap, 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.
+ */
 #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);
+	void *vect = kern_hyp_va(kvm_ksym_ref(__kvm_hyp_vector));
+	int slot = -1;
 
-	if (data->fn) {
-		vect = __bp_harden_hyp_vecs_start +
-		       data->hyp_vectors_slot * SZ_2K;
+	if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR) && data->fn) {
+		vect = kern_hyp_va(kvm_ksym_ref(__bp_harden_hyp_vecs_start));
+		slot = data->hyp_vectors_slot;
+	}
 
-		if (!has_vhe())
-			vect = lm_alias(vect);
+	if (this_cpu_has_cap(ARM64_HARDEN_EL2_VECTORS) && !has_vhe()) {
+		vect = __kvm_bp_vect_base;
+		if (slot == -1)
+			slot = __kvm_harden_el2_vector_slot;
 	}
 
-	vect = kern_hyp_va(vect);
+	if (slot != -1)
+		vect += slot * SZ_2K;
+
 	return vect;
 }
 
+/*  This is only called on a !VHE system */
 static inline int kvm_map_vectors(void)
 {
+	/*
+	 * HBP  = ARM64_HARDEN_BRANCH_PREDICTOR
+	 * HEL2 = ARM64_HARDEN_EL2_VECTORS
+	 *
+	 * !HBP + !HEL2 -> use direct vectors
+	 *  HBP + !HEL2 -> use hardened vectors in place
+	 * !HBP +  HEL2 -> allocate one vector slot and use exec mapping
+	 *  HBP +  HEL2 -> use hardened vertors and use exec mapping
+	 */
+	if (cpus_have_const_cap(ARM64_HARDEN_BRANCH_PREDICTOR)) {
+		__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)) {
+		phys_addr_t vect_pa = __pa_symbol(__bp_harden_hyp_vecs_start);
+		unsigned long size = (__bp_harden_hyp_vecs_end -
+				      __bp_harden_hyp_vecs_start);
+
+		/*
+		 * Always allocate a spare vector slot, as we don't
+		 * know yet which CPUs have a BP hardening slot that
+		 * we can reuse.
+		 */
+		__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)
 {