1 files changed, 41 insertions, 35 deletions

diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 4f74d94c8d97..24b48af27417 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -4,46 +4,52 @@
  *  For licencing details see kernel-base/COPYING
  */
 
-#include <linux/highmem.h>
-#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/export.h>
+#include <linux/instrumented.h>
 
-#include <asm/word-at-a-time.h>
-#include <linux/sched.h>
+#include <asm/tlbflush.h>
 
-/*
- * best effort, GUP based copy_from_user() that is NMI-safe
+/**
+ * copy_from_user_nmi - NMI safe copy from user
+ * @to:		Pointer to the destination buffer
+ * @from:	Pointer to a user space address of the current task
+ * @n:		Number of bytes to copy
+ *
+ * Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied
+ *
+ * Contrary to other copy_from_user() variants this function can be called
+ * from NMI context. Despite the name it is not restricted to be called
+ * from NMI context. It is safe to be called from any other context as
+ * well. It disables pagefaults across the copy which means a fault will
+ * abort the copy.
+ *
+ * For NMI context invocations this relies on the nested NMI work to allow
+ * atomic faults from the NMI path; the nested NMI paths are careful to
+ * preserve CR2.
  */
 unsigned long
 copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
 {
-	unsigned long offset, addr = (unsigned long)from;
-	unsigned long size, len = 0;
-	struct page *page;
-	void *map;
-	int ret;
-
-	if (__range_not_ok(from, n, TASK_SIZE))
-		return len;
-
-	do {
-		ret = __get_user_pages_fast(addr, 1, 0, &page);
-		if (!ret)
-			break;
-
-		offset = addr & (PAGE_SIZE - 1);
-		size = min(PAGE_SIZE - offset, n - len);
-
-		map = kmap_atomic(page);
-		memcpy(to, map+offset, size);
-		kunmap_atomic(map);
-		put_page(page);
-
-		len  += size;
-		to   += size;
-		addr += size;
-
-	} while (len < n);
-
-	return len;
+	unsigned long ret;
+
+	if (!__access_ok(from, n))
+		return n;
+
+	if (!nmi_uaccess_okay())
+		return n;
+
+	/*
+	 * Even though this function is typically called from NMI/IRQ context
+	 * disable pagefaults so that its behaviour is consistent even when
+	 * called from other contexts.
+	 */
+	pagefault_disable();
+	instrument_copy_from_user_before(to, from, n);
+	ret = raw_copy_from_user(to, from, n);
+	instrument_copy_from_user_after(to, from, n, ret);
+	pagefault_enable();
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(copy_from_user_nmi);