KVM: arm64: Unmap 'kvm_arm_hyp_percpu_base' from the host

When pKVM is enabled, the hypervisor at EL2 does not trust the host at
EL1 and must therefore prevent it from having unrestricted access to
internal hypervisor state.

The 'kvm_arm_hyp_percpu_base' array holds the offsets for hypervisor
per-cpu allocations, so move this this into the nVHE code where it
cannot be modified by the untrusted host at EL1.

Tested-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221110190259.26861-22-will@kernel.org

arch/arm64/include/asm/kvm_asm.h

@@ -109,7 +109,7 @@ enum __kvm_host_smccc_func {
 #define per_cpu_ptr_nvhe_sym(sym, cpu)						\
 	({									\
 		unsigned long base, off;					\
-		base = kvm_arm_hyp_percpu_base[cpu];				\
+		base = kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu];		\
 		off = (unsigned long)&CHOOSE_NVHE_SYM(sym) -			\
 		      (unsigned long)&CHOOSE_NVHE_SYM(__per_cpu_start);		\
 		base ? (typeof(CHOOSE_NVHE_SYM(sym))*)(base + off) : NULL;	\
@@ -214,7 +214,7 @@ DECLARE_KVM_HYP_SYM(__kvm_hyp_vector);
 #define __kvm_hyp_init		CHOOSE_NVHE_SYM(__kvm_hyp_init)
 #define __kvm_hyp_vector	CHOOSE_HYP_SYM(__kvm_hyp_vector)
 
-extern unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
+extern unsigned long kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[];
 DECLARE_KVM_NVHE_SYM(__per_cpu_start);
 DECLARE_KVM_NVHE_SYM(__per_cpu_end);
 

arch/arm64/kernel/image-vars.h

@@ -89,9 +89,6 @@ KVM_NVHE_ALIAS(gic_nonsecure_priorities);
 KVM_NVHE_ALIAS(__start___kvm_ex_table);
 KVM_NVHE_ALIAS(__stop___kvm_ex_table);
 
-/* Array containing bases of nVHE per-CPU memory regions. */
-KVM_NVHE_ALIAS(kvm_arm_hyp_percpu_base);
-
 /* PMU available static key */
 #ifdef CONFIG_HW_PERF_EVENTS
 KVM_NVHE_ALIAS(kvm_arm_pmu_available);

arch/arm64/kvm/arm.c

@@ -51,7 +51,6 @@ DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
 DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
-unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
 
 static bool vgic_present;
@@ -1857,13 +1856,13 @@ static void teardown_hyp_mode(void)
 	free_hyp_pgds();
 	for_each_possible_cpu(cpu) {
 		free_page(per_cpu(kvm_arm_hyp_stack_page, cpu));
-		free_pages(kvm_arm_hyp_percpu_base[cpu], nvhe_percpu_order());
+		free_pages(kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu], nvhe_percpu_order());
 	}
 }
 
 static int do_pkvm_init(u32 hyp_va_bits)
 {
-	void *per_cpu_base = kvm_ksym_ref(kvm_arm_hyp_percpu_base);
+	void *per_cpu_base = kvm_ksym_ref(kvm_nvhe_sym(kvm_arm_hyp_percpu_base));
 	int ret;
 
 	preempt_disable();
@@ -1967,7 +1966,7 @@ static int init_hyp_mode(void)
 
 		page_addr = page_address(page);
 		memcpy(page_addr, CHOOSE_NVHE_SYM(__per_cpu_start), nvhe_percpu_size());
-		kvm_arm_hyp_percpu_base[cpu] = (unsigned long)page_addr;
+		kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu] = (unsigned long)page_addr;
 	}
 
 	/*
@@ -2060,7 +2059,7 @@ static int init_hyp_mode(void)
 	}
 
 	for_each_possible_cpu(cpu) {
-		char *percpu_begin = (char *)kvm_arm_hyp_percpu_base[cpu];
+		char *percpu_begin = (char *)kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu];
 		char *percpu_end = percpu_begin + nvhe_percpu_size();
 
 		/* Map Hyp percpu pages */

arch/arm64/kvm/hyp/nvhe/hyp-smp.c

@@ -23,6 +23,8 @@ u64 cpu_logical_map(unsigned int cpu)
 	return hyp_cpu_logical_map[cpu];
 }
 
+unsigned long __ro_after_init kvm_arm_hyp_percpu_base[NR_CPUS];
+
 unsigned long __hyp_per_cpu_offset(unsigned int cpu)
 {
 	unsigned long *cpu_base_array;