From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753056Ab3KOOUy (ORCPT ); Fri, 15 Nov 2013 09:20:54 -0500 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:53847 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752791Ab3KOOUh (ORCPT ); Fri, 15 Nov 2013 09:20:37 -0500 Date: Fri, 15 Nov 2013 14:19:12 +0000 From: Will Deacon To: Konstantin Khlebnikov Cc: Russell King , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Vyacheslav Tyrtov Subject: Re: [PATCH] arm: check stack pointer in get_wchan Message-ID: <20131115141912.GE19468@mudshark.cambridge.arm.com> References: <20131115121907.4707.82671.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131115121907.4707.82671.stgit@buzz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 15, 2013 at 12:19:07PM +0000, Konstantin Khlebnikov wrote: > get_wchan() is lockless. Task may wakeup at any time and change its own stack, > thus each next stack frame may be overwritten and filled with random stuff. > > /proc/$pid/stack interface had been disabled for non-current tasks, see [1] > But 'wchan' still allows to trigger stack frame unwinding on volatile stack. > > This patch fixes oops in unwind_frame() by adding stack pointer validation on > each step (as x86 code do), unwind_frame() already checks frame pointer. > > Also I've found another report of this oops on stackoverflow (irony). For that comment alone: Acked-by: Will Deacon [also, the patch looks sane to me]. Will > Signed-off-by: Konstantin Khlebnikov > Cc: Vyacheslav Tyrtov > Link: http://www.spinics.net/lists/arm-kernel/msg110589.html [1] > Link: http://stackoverflow.com/questions/18479894/unwind-frame-cause-a-kernel-paging-error > --- > arch/arm/kernel/process.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c > index 94f6b05..92f7b15 100644 > --- a/arch/arm/kernel/process.c > +++ b/arch/arm/kernel/process.c > @@ -404,6 +404,7 @@ EXPORT_SYMBOL(dump_fpu); > unsigned long get_wchan(struct task_struct *p) > { > struct stackframe frame; > + unsigned long stack_page; > int count = 0; > if (!p || p == current || p->state == TASK_RUNNING) > return 0; > @@ -412,9 +413,11 @@ unsigned long get_wchan(struct task_struct *p) > frame.sp = thread_saved_sp(p); > frame.lr = 0; /* recovered from the stack */ > frame.pc = thread_saved_pc(p); > + stack_page = (unsigned long)task_stack_page(p); > do { > - int ret = unwind_frame(&frame); > - if (ret < 0) > + if (frame.sp < stack_page || > + frame.sp >= stack_page + THREAD_SIZE || > + unwind_frame(&frame) < 0) > return 0; > if (!in_sched_functions(frame.pc)) > return frame.pc; > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >