From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BA0CC35277 for ; Thu, 6 Aug 2020 11:13:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4D68D22D05 for ; Thu, 6 Aug 2020 11:13:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Bb/cAxUh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729091AbgHFJ1H (ORCPT ); Thu, 6 Aug 2020 05:27:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59368 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729189AbgHFJZG (ORCPT ); Thu, 6 Aug 2020 05:25:06 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2874FC061574 for ; Thu, 6 Aug 2020 02:25:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DKcQQBQJlA+95nyc4B/ghr/B9F2mAty2HjrbxPuzAWQ=; b=Bb/cAxUh4kHkrpPfUunGQ9HQVJ HOhhBKMWGbX7iLIQxhm6oGUQvY9nAbnmjinjvcIbHp5HwdDNo3wZpAJ7lGbqr1XR+YH4HVDlLF/fO eYZOK/+W2pldVk92Z3UdiuWqS21rAPO/NZrTvFhDXzfcAtarVja2q3oRJPjBuc6GSQLJXXAu9lGpj 2kvcgLJ4EwgGz3dhEOf2PMPcYgRC0ABAMBUvkY11LU4W1G+8VWuEouJqX7aa27wAG/u7J7UpfbsZl m56eSiYs0//NC82Wz35rfmsn3RcblL/mavPtegrDVRv4Bxn0UEKUppdtj/B+4UjlMr3DOgYhHHrmN BtBzcK8g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k3c8t-0000gI-KA; Thu, 06 Aug 2020 09:24:56 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 6FF753059DD; Thu, 6 Aug 2020 11:24:54 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 4E3BD23D77450; Thu, 6 Aug 2020 11:24:54 +0200 (CEST) Date: Thu, 6 Aug 2020 11:24:54 +0200 From: peterz@infradead.org To: "Jin, Yao" Cc: mingo@redhat.com, oleg@redhat.com, acme@kernel.org, jolsa@kernel.org, Linux-kernel@vger.kernel.org, ak@linux.intel.com, kan.liang@intel.com, yao.jin@intel.com, alexander.shishkin@linux.intel.com, mark.rutland@arm.com Subject: Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples Message-ID: <20200806092454.GE35926@hirez.programming.kicks-ass.net> References: <20200731025617.16243-1-yao.jin@linux.intel.com> <20200731025617.16243-2-yao.jin@linux.intel.com> <20200804114900.GI2657@hirez.programming.kicks-ass.net> <4c958d61-11a7-9f3e-9e7d-d733270144a1@linux.intel.com> <20200805124454.GP2657@hirez.programming.kicks-ass.net> <797aa4de-c618-f340-ad7b-cef38c96b035@linux.intel.com> <20200806091827.GY2674@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200806091827.GY2674@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 06, 2020 at 11:18:27AM +0200, peterz@infradead.org wrote: > On Thu, Aug 06, 2020 at 10:26:29AM +0800, Jin, Yao wrote: > > > > +static struct pt_regs *sanitize_sample_regs(struct perf_event *event, struct pt_regs *regs) > > > +{ > > > + struct pt_regs *sample_regs = regs; > > > + > > > + /* user only */ > > > + if (!event->attr.exclude_kernel || !event->attr.exclude_hv || > > > + !event->attr.exclude_host || !event->attr.exclude_guest) > > > + return sample_regs; > > > + > > > > Is this condition correct? > > > > Say counting user event on host, exclude_kernel = 1 and exclude_host = 0. It > > will go "return sample_regs" path. > > I'm not sure, I'm terminally confused on virt stuff. [A] > Suppose we have nested virt: > > L0-hv > | > G0/L1-hv > | > G1 > > And we're running in G0, then: > > - 'exclude_hv' would exclude L0 events > - 'exclude_host' would ... exclude L1-hv events? > - 'exclude_guest' would ... exclude G1 events? [B] > Then the next question is, if G0 is a host, does the L1-hv run in > G0 userspace or G0 kernel space? > > I was assuming G0 userspace would not include anything L1 (kvm is a > kernel module after all), but what do I know. > > > > @@ -11609,7 +11636,8 @@ SYSCALL_DEFINE5(perf_event_open, > > > if (err) > > > return err; > > > - if (!attr.exclude_kernel) { > > > + if (!attr.exclude_kernel || !attr.exclude_callchain_kernel || > > > + !attr.exclude_hv || !attr.exclude_host || !attr.exclude_guest) { > > > err = perf_allow_kernel(&attr); > > > if (err) > > > return err; > > > > > > > I can understand the conditions "!attr.exclude_kernel || !attr.exclude_callchain_kernel". > > > > But I'm not very sure about the "!attr.exclude_hv || !attr.exclude_host || !attr.exclude_guest". > > Well, I'm very sure G0 userspace should never see L0 or G1 state, so > exclude_hv and exclude_guest had better be true. > > > On host, exclude_hv = 1, exclude_guest = 1 and exclude_host = 0, right? > > Same as above, is G0 host state G0 userspace? > > > So even exclude_kernel = 1 but exclude_host = 0, we will still go > > perf_allow_kernel path. Please correct me if my understanding is wrong. > > Yes, because with those permission checks in place it means you have > permission to see kernel bits. So if I understand 'exclude_host' wrong -- a distinct possibility -- can we then pretty please have the above [A-B] corrected and put in a comment near perf_event_attr and the exclude_* comments changed to refer to that?