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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>
This commit is contained in:
Peter Zijlstra 2019-04-24 09:19:25 +02:00 committed by Ingo Molnar
parent 6ae865615f
commit 29da93fea3
2 changed files with 5 additions and 4 deletions
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5
lib/strncpy_from_user.c
View File

@ -23,10 +23,11 @@
* hit it), 'max' is the address space maximum (and we return * hit it), 'max' is the address space maximum (and we return
* -EFAULT if we hit it). * -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; 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 * Truncate 'max' to the user-specified limit, so that

4
lib/strnlen_user.c
View File

@ -28,7 +28,7 @@
static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) 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; const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
long align, res = 0; unsigned long align, res = 0;
unsigned long c; 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 * Do everything aligned. But that means that we
* need to also expand the maximum.. * need to also expand the maximum..
*/ */
align = (sizeof(long) - 1) & (unsigned long)src; align = (sizeof(unsigned long) - 1) & (unsigned long)src;
src -= align; src -= align;
max += align; max += align;