1 files changed, 33 insertions, 0 deletions
diff --git a/arch/x86/mm/maccess.c b/arch/x86/mm/maccess.c
new file mode 100644
index 0000000000..6993f026ad
--- /dev/null
+++ b/arch/x86/mm/maccess.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/uaccess.h>
+#include <linux/kernel.h>
+
+#ifdef CONFIG_X86_64
+bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
+{
+	unsigned long vaddr = (unsigned long)unsafe_src;
+
+	/*
+	 * Do not allow userspace addresses.  This disallows
+	 * normal userspace and the userspace guard page:
+	 */
+	if (vaddr < TASK_SIZE_MAX + PAGE_SIZE)
+		return false;
+
+	/*
+	 * Allow everything during early boot before 'x86_virt_bits'
+	 * is initialized.  Needed for instruction decoding in early
+	 * exception handlers.
+	 */
+	if (!boot_cpu_data.x86_virt_bits)
+		return true;
+
+	return __is_canonical_address(vaddr, boot_cpu_data.x86_virt_bits);
+}
+#else
+bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
+{
+	return (unsigned long)unsafe_src >= TASK_SIZE_MAX;
+}
+#endif