mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions

Randy reported objtool triggered on his (GCC-7.4) build:

  lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x315: call to __ubsan_handle_add_overflow() with UACCESS enabled
  lib/strnlen_user.o: warning: objtool: strnlen_user()+0x337: call to __ubsan_handle_sub_overflow() with UACCESS enabled

This is due to UBSAN generating signed-overflow-UB warnings where it
should not. Prior to GCC-8 UBSAN ignored -fwrapv (which the kernel
uses through -fno-strict-overflow).

Make the functions use 'unsigned long' throughout.

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: luto@kernel.org
Link: http://lkml.kernel.org/r/20190424072208.754094071@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 5 insertions, 4 deletions

diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index 58eacd41526c..023ba9f3b99f 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -23,10 +23,11 @@
  * hit it), 'max' is the address space maximum (and we return
  * -EFAULT if we hit it).
  */
-static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
+static inline long do_strncpy_from_user(char *dst, const char __user *src,
+                                        unsigned long count, unsigned long max)
 {
         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
-        long res = 0;
+        unsigned long res = 0;
 
         /*
          * Truncate 'max' to the user-specified limit, so that
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 1c1a1b0e38a5..7f2db3fe311f 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -28,7 +28,7 @@
 static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
 {
         const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
-        long align, res = 0;
+        unsigned long align, res = 0;
         unsigned long c;
 
         /*
@@ -42,7 +42,7 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
          * Do everything aligned. But that means that we
          * need to also expand the maximum..
          */
-        align = (sizeof(long) - 1) & (unsigned long)src;
+        align = (sizeof(unsigned long) - 1) & (unsigned long)src;
         src -= align;
         max += align;