From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754662AbZHYJLs (ORCPT ); Tue, 25 Aug 2009 05:11:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752776AbZHYJLr (ORCPT ); Tue, 25 Aug 2009 05:11:47 -0400 Received: from courier.cs.helsinki.fi ([128.214.9.1]:54554 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752791AbZHYJLq (ORCPT ); Tue, 25 Aug 2009 05:11:46 -0400 Subject: Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() From: Pekka Enberg To: Vegard Nossum Cc: Ingo Molnar , Catalin Marinas , linux-kernel@vger.kernel.org In-Reply-To: <19f34abd0908250203h52257f52v306545a3d8890577@mail.gmail.com> References: <20090825071959.GA25877@elte.hu> <19f34abd0908250104y6e877545y485a2104c2b97cfd@mail.gmail.com> <20090825083222.GC17692@elte.hu> <1251189914.7261.11.camel@penberg-laptop> <20090825084808.GA14003@elte.hu> <1251190466.7261.12.camel@penberg-laptop> <19f34abd0908250203h52257f52v306545a3d8890577@mail.gmail.com> Date: Tue, 25 Aug 2009 12:11:47 +0300 Message-Id: <1251191507.26351.0.camel@penberg-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit X-Mailer: Evolution 2.24.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-08-25 at 11:03 +0200, Vegard Nossum wrote: > I don't know so much about the kmemleak internals, but this I can say > about the kmemcheck part: According to your definition, an object is > initialized if all the bytes of an object are initialized. > > Is it possible that because of this, if we have a partially > uninitialized object, kmemleak will not record the pointers found in > that object? If so, it might skip valid pointers, and deem an object > unreferenced. Which could make kmemleak give false-positives. > > I think it would be better to ask kmemcheck on a per-pointer basis > (i.e. for each pointer-sized word in the object), whether it is > initialized or not. Yeah, makes sense. Pekka diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c index 2c55ed0..528bf95 100644 --- a/arch/x86/mm/kmemcheck/kmemcheck.c +++ b/arch/x86/mm/kmemcheck/kmemcheck.c @@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs, kmemcheck_shadow_set(shadow, size); } +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + enum kmemcheck_shadow status; + void *shadow; + + shadow = kmemcheck_shadow_lookup(addr); + if (!shadow) + return true; + + status = kmemcheck_shadow_test(shadow, size); + + return status == KMEMCHECK_SHADOW_INITIALIZED; +} + /* Access may cross page boundary */ static void kmemcheck_read(struct pt_regs *regs, unsigned long addr, unsigned int size) diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h index 47b39b7..dc2fd54 100644 --- a/include/linux/kmemcheck.h +++ b/include/linux/kmemcheck.h @@ -34,6 +34,8 @@ void kmemcheck_mark_initialized_pages(struct page *p, unsigned int n); int kmemcheck_show_addr(unsigned long address); int kmemcheck_hide_addr(unsigned long address); +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size); + #else #define kmemcheck_enabled 0 @@ -99,6 +101,11 @@ static inline void kmemcheck_mark_initialized_pages(struct page *p, { } +static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) +{ + return true; +} + #endif /* CONFIG_KMEMCHECK */ /* diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 6debe0d..b075bf0 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -97,6 +97,7 @@ #include #include +#include #include /* @@ -885,7 +886,8 @@ static void scan_block(void *_start, void *_end, for (ptr = start; ptr < end; ptr++) { unsigned long flags; - unsigned long pointer = *ptr; + unsigned long pointer; + struct kmemleak_object *object; if (allow_resched) @@ -893,6 +895,13 @@ static void scan_block(void *_start, void *_end, if (scan_should_stop()) break; + /* Don't scan uninitialized memory. */ + if (!kmemcheck_is_obj_initialized((unsigned long) ptr, + sizeof(unsigned long))) + continue; + + pointer = *ptr; + object = find_and_get_object(pointer, 1); if (!object) continue;