From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752098AbbJTLDg (ORCPT ); Tue, 20 Oct 2015 07:03:36 -0400 Received: from casper.infradead.org ([85.118.1.10]:53405 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751140AbbJTLDf (ORCPT ); Tue, 20 Oct 2015 07:03:35 -0400 Date: Tue, 20 Oct 2015 13:03:32 +0200 From: Peter Zijlstra To: Andi Kleen Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Andi Kleen Subject: Re: [PATCH 2/2] x86, perf: Optimize stack walk user accesses Message-ID: <20151020110332.GB17308@twins.programming.kicks-ass.net> References: <1445295269-5672-1-git-send-email-andi@firstfloor.org> <1445295269-5672-2-git-send-email-andi@firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1445295269-5672-2-git-send-email-andi@firstfloor.org> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 19, 2015 at 03:54:29PM -0700, Andi Kleen wrote: > @@ -2307,7 +2312,13 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) > frame.next_frame = NULL; > frame.return_address = 0; > > - bytes = copy_from_user_nmi(&frame, fp, sizeof(frame)); > + if (!access_ok(VERIFY_READ, fp, 16)) > + break; > + > + bytes = __copy_from_user_nmi(&frame.next_frame, fp, 8); > + if (bytes != 0) > + break; > + bytes = __copy_from_user_nmi(&frame.return_address, fp+8, 8); > if (bytes != 0) > break; > The previous patch that introduces this function states that any caller must have pagefault_disable() or be from interrupt context. Perf can call this function from !interrupt context (imagine a tracepoint or other software event), should we therefore not add a pagefault_disable()/enable() pair around the entire while() loop?