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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 8E841C2D0E4 for ; Tue, 24 Nov 2020 07:50:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 193D220719 for ; Tue, 24 Nov 2020 07:50:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="n0ZrSFvE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729715AbgKXHuG (ORCPT ); Tue, 24 Nov 2020 02:50:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727840AbgKXHuG (ORCPT ); Tue, 24 Nov 2020 02:50:06 -0500 Received: from mail-yb1-xb43.google.com (mail-yb1-xb43.google.com [IPv6:2607:f8b0:4864:20::b43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DD2FC0613CF; Mon, 23 Nov 2020 23:50:06 -0800 (PST) Received: by mail-yb1-xb43.google.com with SMTP id w5so18406134ybj.11; Mon, 23 Nov 2020 23:50:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=MCr9yurgtDaUMxiJ7mKazCnLV7ap7nqWiu58RHAmVXo=; b=n0ZrSFvEhkTdK67AHyeDFOfteccD81MLY1pAIi9xWhMfZr/qzK7RSsCgk3/64FxpPb lGUSK9cbACu01OVqDTK+bixulzFDQzMESUevN8RvWpNXSvukq5KCtLL4awnB35pBRTBd oekBo6Vm9wcJscdKRuTMAvjsJr7jWcd2PtuMpvck6HBuO1ZM2P5HmYeldAFYgfxZ2A51 rggEt0eJE6p4lywtol2/ozGFprg54MM8FQOglp7jz7NIRs0NskfJFguOzmw03gbOAbWw ZFjHYJDWQAiapJg287MK6aWQM80F8AHkMnCaV12YZhD7FE+9tsXWhvGKxH1cBEjtmaos RXGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=MCr9yurgtDaUMxiJ7mKazCnLV7ap7nqWiu58RHAmVXo=; b=IuEUaVvz5Z7BnujDZoI17jSWEtwLj1THqq77FAg0awfAxdIlrK7+EM/TfJmnfWpLGy tlgImZ5HhWwKE0GVsRROd7fDQNeXbREDyGDeNVf7ss7feEuUdokPXjAvbkY7qQ27AwR1 j3gsMHlbsqkOwwj3jNFHQNuIHVfYy4m5ZdZ3fK7hRjmYv87U2iDKmC22Vt0uVnkZ9gqU xL30vAiz6K2wk3e+nnsXBGqZrX+qXhVecSRTNjr94BDAUAjUO/LbKAt/Zu2qBrFKMi57 YHeS0Wsd0ihxsEWbOrdpB59jTWavcjB2kt+lC9FGPaz38V0ekN63NzIUzyZH/5N5rL/v cf/Q== X-Gm-Message-State: AOAM531stn4q98oPhomWm2CIyI5UutCfnVrEuDRzkf0cB+Xzl5qvaEk6 UgHg41oC2D/m4Jd6IDyIwAOC9J6A59GBFnpicsO1wXm5TVc= X-Google-Smtp-Source: ABdhPJx34S4tI2/pz6jPfz2xAj+di1kmGKUBFtkiuqP/9HJ3DpPG5JxcoTyId50E88zowAm6tiwSTqNC0GpGANq5uNQ= X-Received: by 2002:a25:df82:: with SMTP id w124mr4702486ybg.347.1606204205135; Mon, 23 Nov 2020 23:50:05 -0800 (PST) MIME-Version: 1.0 References: <20201119232244.2776720-1-andrii@kernel.org> <20201119232244.2776720-2-andrii@kernel.org> <20201124054924.i7zq7vig4xqmddyr@ast-mbp> In-Reply-To: <20201124054924.i7zq7vig4xqmddyr@ast-mbp> From: Andrii Nakryiko Date: Mon, 23 Nov 2020 23:49:54 -0800 Message-ID: Subject: Re: [PATCH bpf-next 1/6] bpf: fix bpf_put_raw_tracepoint()'s use of __module_address() To: Alexei Starovoitov Cc: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Mon, Nov 23, 2020 at 9:49 PM Alexei Starovoitov wrote: > > On Thu, Nov 19, 2020 at 03:22:39PM -0800, Andrii Nakryiko wrote: > > __module_address() needs to be called with preemption disabled or with > > module_mutex taken. preempt_disable() is enough for read-only uses, which is > > what this fix does. > > > > Fixes: a38d1107f937 ("bpf: support raw tracepoints in modules") > > Signed-off-by: Andrii Nakryiko > > --- > > kernel/trace/bpf_trace.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index d255bc9b2bfa..bb98a377050a 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -2060,7 +2060,11 @@ struct bpf_raw_event_map *bpf_get_raw_tracepoint(const char *name) > > > > void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp) > > { > > - struct module *mod = __module_address((unsigned long)btp); > > + struct module *mod; > > + > > + preempt_disable(); > > + mod = __module_address((unsigned long)btp); > > + preempt_enable(); > > > > if (mod) > > module_put(mod); > > I don't understand why 'mod' cannot become dangling pointer after preempt_enable(). > Either it needs a comment explaining why it's ok or module_put() should > be in preempt disabled section. Yeah, I think it can, assuming the kernel module can be unloaded despite non-zero refcnt (probably happens with force unload?). I'll drop the `if (mod)` part (module_put() checks that internally) and will move module_put(mod) inside the preempt disable/enable region.