KVM: arm64: Restrict EL2 stage-1 changes in protected mode

The host kernel is currently able to change EL2 stage-1 mappings without
restrictions thanks to the __pkvm_create_mappings() hypercall. But in a
world where the host is no longer part of the TCB, this clearly poses a
problem.

To fix this, introduce a new hypercall to allow the host to share a
physical memory page with the hypervisor, and remove the
__pkvm_create_mappings() variant. The new hypercall implements
ownership and permission checks before allowing the sharing operation,
and it annotates the shared page in the hypervisor stage-1 and host
stage-2 page-tables.

Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210809152448.1810400-21-qperret@google.com

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 432a9ea1f02e9044c3a88ca90d641e76913f5ce6..aed2aa61766aa4f86d16d186b126c1a358a649e5 100644 (file)
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -59,7 +59,7 @@
 #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs              13
 #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs           14
 #define __KVM_HOST_SMCCC_FUNC___pkvm_init                      15
-#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings           16
+#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp            16
 #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping    17
 #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector            18
 #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize             19

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 0118527b07b06cc53a9ae096db1dc6b12b2c60c6..03e604f842e2b3fc36edfe3e6ac97a481feab56f 100644 (file)
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -49,6 +49,7 @@ extern struct host_kvm host_kvm;
 extern const u8 pkvm_hyp_id;
 
 int __pkvm_prot_finalize(void);
+int __pkvm_host_share_hyp(u64 pfn);
 
 bool addr_is_memory(phys_addr_t phys);
 int host_stage2_idmap_locked(phys_addr_t addr, u64 size, enum kvm_pgtable_prot prot);

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 7900d5b66ba3c7ff4552eaafe5928264c7090036..2da6aa8da8680d1e6c17415e0ee16d13fd26d3bc 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -140,14 +140,11 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt)
        cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot);
 }
 
-static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt)
+static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt)
 {
-       DECLARE_REG(unsigned long, start, host_ctxt, 1);
-       DECLARE_REG(unsigned long, size, host_ctxt, 2);
-       DECLARE_REG(unsigned long, phys, host_ctxt, 3);
-       DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4);
+       DECLARE_REG(u64, pfn, host_ctxt, 1);
 
-       cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot);
+       cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(pfn);
 }
 
 static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt)
@@ -185,7 +182,7 @@ static const hcall_t host_hcall[] = {
        HANDLE_FUNC(__vgic_v3_restore_aprs),
        HANDLE_FUNC(__pkvm_init),
        HANDLE_FUNC(__pkvm_cpu_set_vector),
-       HANDLE_FUNC(__pkvm_create_mappings),
+       HANDLE_FUNC(__pkvm_host_share_hyp),
        HANDLE_FUNC(__pkvm_create_private_mapping),
        HANDLE_FUNC(__pkvm_prot_finalize),
 };

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index 2991dc6996b9e4737ef228bbfa3d859202608b8a..8165390d3ec997f4bb546abf8ca092987e90a91d 100644 (file)
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -339,6 +339,94 @@ unlock:
        return ret;
 }
 
+static inline bool check_prot(enum kvm_pgtable_prot prot,
+                             enum kvm_pgtable_prot required,
+                             enum kvm_pgtable_prot denied)
+{
+       return (prot & (required | denied)) == required;
+}
+
+int __pkvm_host_share_hyp(u64 pfn)
+{
+       phys_addr_t addr = hyp_pfn_to_phys(pfn);
+       enum kvm_pgtable_prot prot, cur;
+       void *virt = __hyp_va(addr);
+       enum pkvm_page_state state;
+       kvm_pte_t pte;
+       int ret;
+
+       if (!addr_is_memory(addr))
+               return -EINVAL;
+
+       hyp_spin_lock(&host_kvm.lock);
+       hyp_spin_lock(&pkvm_pgd_lock);
+
+       ret = kvm_pgtable_get_leaf(&host_kvm.pgt, addr, &pte, NULL);
+       if (ret)
+               goto unlock;
+       if (!pte)
+               goto map_shared;
+
+       /*
+        * Check attributes in the host stage-2 PTE. We need the page to be:
+        *  - mapped RWX as we're sharing memory;
+        *  - not borrowed, as that implies absence of ownership.
+        * Otherwise, we can't let it got through
+        */
+       cur = kvm_pgtable_stage2_pte_prot(pte);
+       prot = pkvm_mkstate(0, PKVM_PAGE_SHARED_BORROWED);
+       if (!check_prot(cur, PKVM_HOST_MEM_PROT, prot)) {
+               ret = -EPERM;
+               goto unlock;
+       }
+
+       state = pkvm_getstate(cur);
+       if (state == PKVM_PAGE_OWNED)
+               goto map_shared;
+
+       /*
+        * Tolerate double-sharing the same page, but this requires
+        * cross-checking the hypervisor stage-1.
+        */
+       if (state != PKVM_PAGE_SHARED_OWNED) {
+               ret = -EPERM;
+               goto unlock;
+       }
+
+       ret = kvm_pgtable_get_leaf(&pkvm_pgtable, (u64)virt, &pte, NULL);
+       if (ret)
+               goto unlock;
+
+       /*
+        * If the page has been shared with the hypervisor, it must be
+        * already mapped as SHARED_BORROWED in its stage-1.
+        */
+       cur = kvm_pgtable_hyp_pte_prot(pte);
+       prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
+       if (!check_prot(cur, prot, ~prot))
+               ret = EPERM;
+       goto unlock;
+
+map_shared:
+       /*
+        * If the page is not yet shared, adjust mappings in both page-tables
+        * while both locks are held.
+        */
+       prot = pkvm_mkstate(PAGE_HYP, PKVM_PAGE_SHARED_BORROWED);
+       ret = pkvm_create_mappings_locked(virt, virt + PAGE_SIZE, prot);
+       BUG_ON(ret);
+
+       prot = pkvm_mkstate(PKVM_HOST_MEM_PROT, PKVM_PAGE_SHARED_OWNED);
+       ret = host_stage2_idmap_locked(addr, PAGE_SIZE, prot);
+       BUG_ON(ret);
+
+unlock:
+       hyp_spin_unlock(&pkvm_pgd_lock);
+       hyp_spin_unlock(&host_kvm.lock);
+
+       return ret;
+}
+
 void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 {
        struct kvm_vcpu_fault_info fault;

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 0625bf2353c2297babea82e642a8b84d75b91577..cbab146cda6ada69d4cd074e2c3ec78ed5406ea3 100644 (file)
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -259,10 +259,8 @@ static int __create_hyp_mappings(unsigned long start, unsigned long size,
 {
        int err;
 
-       if (!kvm_host_owns_hyp_mappings()) {
-               return kvm_call_hyp_nvhe(__pkvm_create_mappings,
-                                        start, size, phys, prot);
-       }
+       if (WARN_ON(!kvm_host_owns_hyp_mappings()))
+               return -EINVAL;
 
        mutex_lock(&kvm_hyp_pgd_mutex);
        err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot);
@@ -282,6 +280,21 @@ static phys_addr_t kvm_kaddr_to_phys(void *kaddr)
        }
 }
 
+static int pkvm_share_hyp(phys_addr_t start, phys_addr_t end)
+{
+       phys_addr_t addr;
+       int ret;
+
+       for (addr = ALIGN_DOWN(start, PAGE_SIZE); addr < end; addr += PAGE_SIZE) {
+               ret = kvm_call_hyp_nvhe(__pkvm_host_share_hyp,
+                                       __phys_to_pfn(addr));
+               if (ret)
+                       return ret;
+       }
+
+       return 0;
+}
+
 /**
  * create_hyp_mappings - duplicate a kernel virtual address range in Hyp mode
  * @from:      The virtual kernel start address of the range
@@ -302,6 +315,13 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
        if (is_kernel_in_hyp_mode())
                return 0;
 
+       if (!kvm_host_owns_hyp_mappings()) {
+               if (WARN_ON(prot != PAGE_HYP))
+                       return -EPERM;
+               return pkvm_share_hyp(kvm_kaddr_to_phys(from),
+                                     kvm_kaddr_to_phys(to));
+       }
+
        start = start & PAGE_MASK;
        end = PAGE_ALIGN(end);