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From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de, x86@kernel.org
Cc: linux-kernel@vger.kernel.org, luto@kernel.org,
	peterz@infradead.org, Randy Dunlap <rdunlap@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 2/2] mm/uaccess: Use unsigned long
Date: Wed, 24 Apr 2019 09:19:25 +0200
Message-ID: <20190424072208.754094071@infradead.org> (raw)
In-Reply-To: <20190424071923.275371441@infradead.org>

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>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 lib/strncpy_from_user.c |    5 +++--
 lib/strnlen_user.c      |    4 ++--
 2 files changed, 5 insertions(+), 4 deletions(-)

--- 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
--- 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
 	 * 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;
 



  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-24  7:19 [PATCH 0/2] objtool uaccess fixes Peter Zijlstra
2019-04-24  7:19 ` [PATCH 1/2] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation Peter Zijlstra
2019-04-24 11:10   ` [tip:core/objtool] " tip-bot for Peter Zijlstra
2019-04-24  7:19 ` Peter Zijlstra [this message]
2019-04-24 11:10   ` [tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions tip-bot for Peter Zijlstra

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