x86/sgx: Create utility to validate user provided offset and length

User provided offset and length is validated when parsing the parameters
of the SGX_IOC_ENCLAVE_ADD_PAGES ioctl(). Extract this validation
(with consistent use of IS_ALIGNED) into a utility that can be used
by the SGX2 ioctl()s that will also provide these values.
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/767147bc100047abed47fe27c592901adfbb93a2.1652137848.git.reinette.chatre@intel.com

arch/x86/kernel/cpu/sgx/ioctl.c

@@ -372,6 +372,26 @@ static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long src,
 	return ret;
 }
 
+/*
+ * Ensure user provided offset and length values are valid for
+ * an enclave.
+ */
+static int sgx_validate_offset_length(struct sgx_encl *encl,
+				      unsigned long offset,
+				      unsigned long length)
+{
+	if (!IS_ALIGNED(offset, PAGE_SIZE))
+		return -EINVAL;
+
+	if (!length || !IS_ALIGNED(length, PAGE_SIZE))
+		return -EINVAL;
+
+	if (offset + length - PAGE_SIZE >= encl->size)
+		return -EINVAL;
+
+	return 0;
+}
+
 /**
  * sgx_ioc_enclave_add_pages() - The handler for %SGX_IOC_ENCLAVE_ADD_PAGES
  * @encl:       an enclave pointer
@@ -425,14 +445,10 @@ static long sgx_ioc_enclave_add_pages(struct sgx_encl *encl, void __user *arg)
 	if (copy_from_user(&add_arg, arg, sizeof(add_arg)))
 		return -EFAULT;
 
-	if (!IS_ALIGNED(add_arg.offset, PAGE_SIZE) ||
-	    !IS_ALIGNED(add_arg.src, PAGE_SIZE))
-		return -EINVAL;
-
-	if (!add_arg.length || add_arg.length & (PAGE_SIZE - 1))
+	if (!IS_ALIGNED(add_arg.src, PAGE_SIZE))
 		return -EINVAL;
 
-	if (add_arg.offset + add_arg.length - PAGE_SIZE >= encl->size)
+	if (sgx_validate_offset_length(encl, add_arg.offset, add_arg.length))
 		return -EINVAL;
 
 	if (copy_from_user(&secinfo, (void __user *)add_arg.secinfo,