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-rw-r--r--arch/x86/mm/maccess.c33
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