[PATCH 2/2] KVM: Validate userspace_addr of memslot when registered

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

From: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>

This way, we can avoid checking the user space address many times when
we read the guest memory.

Although we can do the same for write if we check which slots are
writable, we do not care write now: reading the guest memory happens
more often than writing.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
---
 arch/x86/kvm/paging_tmpl.h |    2 +-
 virt/kvm/kvm_main.c        |    7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 0803e36..6c4dc01 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -183,7 +183,7 @@ walk:
 		}
 
 		ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
-		if (unlikely(copy_from_user(&pte, ptep_user, sizeof(pte)))) {
+		if (unlikely(__copy_from_user(&pte, ptep_user, sizeof(pte)))) {
 			present = false;
 			break;
 		}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5814645..0402b6b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -648,7 +648,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		goto out;
 	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
 		goto out;
-	if (user_alloc && (mem->userspace_addr & (PAGE_SIZE - 1)))
+	/* We can read the guest memory with __xxx_user() later on. */
+	if (user_alloc &&
+	    ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
+	     !access_ok(VERIFY_READ, mem->userspace_addr, mem->memory_size)))
 		goto out;
 	if (mem->slot >= KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS)
 		goto out;
@@ -1283,7 +1286,7 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
 	addr = gfn_to_hva(kvm, gfn);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
-	r = copy_from_user(data, (void __user *)addr + offset, len);
+	r = __copy_from_user(data, (void __user *)addr + offset, len);
 	if (r)
 		return -EFAULT;
 	return 0;
-- 
1.7.1