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bh=/9EsnOGzOhPR6QqbkJOoiHVayjiazyxeJO1u9uDG23U=; b=G4UhM2MN/4XPfJQ4IpBmnp1sFIQMHZWrNrma6Ew/rNQ1htNIPWW0PqqylBxoi8S6vIA+Qu E14Sb2s8DeChOUrk1q/Viu5tw358I9E/mqwN+l2jaIAVeZg+64pQWBy0I1/ETg+0bhsX2E Zw7UL/ul9sc82jUgSzK7PjamaWrzHPg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-534-VRELtzg0MUiEtHlptNYnSw-1; Wed, 16 Sep 2020 12:17:02 -0400 X-MC-Unique: VRELtzg0MUiEtHlptNYnSw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 29B3E425CE for ; Wed, 16 Sep 2020 16:17:01 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-113-131.ams2.redhat.com [10.36.113.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2B4B71002D41; Wed, 16 Sep 2020 16:16:57 +0000 (UTC) Subject: Re: [PATCH] hw/nvram/fw_cfg: Assert linked data is not NULL To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org References: <20200916140535.1451663-1-philmd@redhat.com> From: Laszlo Ersek Message-ID: <7fe3ec9c-2ffb-7003-d189-5920ac124541@redhat.com> Date: Wed, 16 Sep 2020 18:16:56 +0200 MIME-Version: 1.0 In-Reply-To: <20200916140535.1451663-1-philmd@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lersek@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US Received-SPF: pass client-ip=63.128.21.124; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/16 02:35:56 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -50 X-Spam_score: -5.1 X-Spam_bar: ----- X-Spam_report: (-5.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.999, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Phil, On 09/16/20 16:05, Philippe Mathieu-Daudé wrote: > The linked data passed to the fw_cfg device must not be NULL. > Add an assertion. > > Reported-by: Laszlo Ersek > Signed-off-by: Philippe Mathieu-Daudé > --- > hw/nvram/fw_cfg.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c > index f3a4728288e..40dcc08b57b 100644 > --- a/hw/nvram/fw_cfg.c > +++ b/hw/nvram/fw_cfg.c > @@ -711,6 +711,7 @@ static void fw_cfg_add_bytes_callback(FWCfgState *s, uint16_t key, > > key &= FW_CFG_ENTRY_MASK; > > + assert(data); > assert(key < fw_cfg_max_entry(s) && len < UINT32_MAX); > assert(s->entries[arch][key].data == NULL); /* avoid key conflict */ > > (1) this assert() would fire without my [PATCH] hw/nvram/fw_cfg: fix FWCfgDataGeneratorClass::get_data() consumption so minimally we should apply your patch only after mine. (2) I'm unsure if it's *always* a programming error to link a NULL datum under an fw_cfg key. The reader functions fw_cfg_data_read() and fw_cfg_dma_transfer() deal with NULL data gracefully. I think we should add the assert() only if we can prove that "include/hw/nvram/fw_cfg.h" already forbids callers from passing in NULL data. Otherwise, we'll have to audit all the fw-cfg-add-xxx call sites, extend the comments in the header file, and *then* add the assert(). For now I'd only go with the patch I posted. Thanks! Laszlo