linux-kernel - [tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions

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Message-ID: <tip-29da93fea3ea39ab9b12270cc6be1b70ef201c9e@git.kernel.org>
Date:   Wed, 24 Apr 2019 04:10:49 -0700
From:   tip-bot for Peter Zijlstra <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     rdunlap@...radead.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        hpa@...or.com, tglx@...utronix.de, mingo@...nel.org
Subject: [tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN
 warnings on older GCC versions

Commit-ID:  29da93fea3ea39ab9b12270cc6be1b70ef201c9e
Gitweb:     https://git.kernel.org/tip/29da93fea3ea39ab9b12270cc6be1b70ef201c9e
Author:     Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 24 Apr 2019 09:19:25 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 24 Apr 2019 12:19:45 +0200

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@...radead.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Randy Dunlap <rdunlap@...radead.org> # build-tested
Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: luto@...nel.org
Link: http://lkml.kernel.org/r/20190424072208.754094071@infradead.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 lib/strncpy_from_user.c | 5 +++--
 lib/strnlen_user.c      | 4 ++--
 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;