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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 39A84C61DD3 for ; Wed, 2 Sep 2026 00:54:54 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2362110EF84; Wed, 2 Sep 2026 00:54:53 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="DKk7DqAc"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) by gabe.freedesktop.org (Postfix) with ESMTPS id 8F57510EF76; Wed, 2 Sep 2026 00:54:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1788310492; x=1819846492; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=S2jRmT3i4CUHeBAmwKFhWwEWN2ceCfdeY5JxH6o4MBg=; b=DKk7DqAc6/FE4XFPHd7JPXCFN+ijYD+X0V8RS2IahZPCLpkoiuqJ4DXD tYjuIvNb70eu+Qmh9djKHWbYYZHJQUyEICJi1HJm/CG94buAe/2/1g9wG 29+1JWXq1nwstJaagkmKsLiH6aD86yAjrmsLQt1QUTUk50TIDHZMDO7R2 kFIYzJc85wj3Pe0zrQWIMTXA/hqvLWqHbcqeJHfTaCxD5vD0xcjel8kZt KsiDnqokEkB5tvbjd6EEgiEbK6Wz68A2O0g2f0VJ7ygF0TK/PP9UjNk1l JH3BwLqcVPp2l1u6D4wpLP390aUb6tWK6YUDyL7kQi1cbmCWZjiqB/bwf Q==; X-CSE-ConnectionGUID: RgC1GnhzTFqEQ5+btC7lLQ== X-CSE-MsgGUID: BKcLZgEbScGxpWOf5gAqYg== X-IronPort-AV: E=McAfee;i="6800,10657,11893"; a="92626697" X-IronPort-AV: E=Sophos;i="6.25,257,1779174000"; d="scan'208";a="92626697" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2026 17:54:50 -0700 X-CSE-ConnectionGUID: 6jThSNJbRXW4XHMxVAKrGw== X-CSE-MsgGUID: bqJkn67PTt613PaKElruHQ== X-ExtLoop1: 1 Received: from dapengmi-mobl1.ccr.corp.intel.com (HELO [10.124.241.239]) ([10.124.241.239]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2026 17:54:48 -0700 Message-ID: Date: Wed, 2 Sep 2026 08:54:46 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/2] perf: Fix null pointer access in is_include_guest_event() To: Vinay Belgaumkar , intel-xe@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org, Alexander Kanevskiy References: <20260901211915.127704-1-vinay.belgaumkar@intel.com> <20260901211915.127704-2-vinay.belgaumkar@intel.com> Content-Language: en-US From: "Mi, Dapeng" In-Reply-To: <20260901211915.127704-2-vinay.belgaumkar@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 9/2/2026 5:19 AM, Vinay Belgaumkar wrote: > A typical module unload occurring event when there is an active perf > connection leads to freeing of the pmu pointer. The call log is something > like: > .. > __pmu_detach_event > pmu_detach_event > pmu_detach_events > perf_pmu_unregister > .. > > __pmu_detach_event() sets event->pmu to null. When the perf connection > finally is closed, the following stack trace is observed: > > Oops: general protection fault, kernel NULL pointer dereference > ... > RIP: 0010:_free_event+0x3e/0x370 > ... > Call Trace: > ... > perf_event_release_kernel+0x260/0x2d0 > perf_release+0x12/0x20 > > A call to mediated_pmu_unaccount_event() inside _free_event() is the root > cause of this crash. Adding a check to is_include_guest_event() ensures > we don't accidentally access a null ptr. Better mention adding an extra mediated_pmu_unaccount_event() call before clearing event->pmu to ensure the nr_include_guest_events count is correctly decreased. > > v2: Add another check to prevent null access (sashiko) > v3: Use READ_ONCE for checking pmu state (sashiko) > v4: READ_ONCE for the pmu check as well (sashiko) > v5: Improve commit message and split patch into 2 (Dapeng) Please remove this version history in the formal patch. Others look good to me. Thanks. > > Fixes: eff95e170275 ("perf: Add APIs to create/release mediated guest vPMUs") > Cc: Alexander Kanevskiy > Cc: Dapeng Mi > Assisted-by: Claude:Claude-Sonnet-5 > Signed-off-by: Vinay Belgaumkar > --- > kernel/events/core.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 94ca277e0819..f19d27ac411d 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -6350,6 +6350,9 @@ static DEFINE_MUTEX(perf_mediated_pmu_mutex); > /* !exclude_guest event of PMU with PERF_PMU_CAP_MEDIATED_VPMU */ > static inline bool is_include_guest_event(struct perf_event *event) > { > + if (!event->pmu) > + return false; > + > if ((event->pmu->capabilities & PERF_PMU_CAP_MEDIATED_VPMU) && > !event->attr.exclude_guest) > return true; > @@ -12977,6 +12980,7 @@ static void __pmu_detach_event(struct pmu *pmu, struct perf_event *event, > exclusive_event_destroy(event); > module_put(pmu->module); > > + mediated_pmu_unaccount_event(event); > event->pmu = NULL; /* force fault instead of UAF */ > } >