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[90.40.114.60]) by smtp.gmail.com with ESMTPSA id m184sm2418932wme.40.2021.05.06.02.01.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 May 2021 02:01:55 -0700 (PDT) Subject: Re: [PATCH 06/23] hw/block/dataplane/virtio-blk: Avoid dynamic stack allocation To: Stefan Hajnoczi References: <20210505211047.1496765-1-philmd@redhat.com> <20210505211047.1496765-7-philmd@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <124ddeb2-ca4a-c551-19ad-d1125451226f@redhat.com> Date: Thu, 6 May 2021 11:01:47 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=WINDOWS-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.693, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=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: Kevin Wolf , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , qemu-block@nongnu.org, Richard Henderson , qemu-devel@nongnu.org, Max Reitz , qemu-ppc@nongnu.org, Gerd Hoffmann , Paolo Bonzini , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/6/21 10:53 AM, Stefan Hajnoczi wrote: > On Wed, May 05, 2021 at 11:10:30PM +0200, Philippe Mathieu-Daudé wrote: >> Use autofree heap allocation instead of variable-length >> array on the stack. >> >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> hw/block/dataplane/virtio-blk.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) > > Why? The motivation behind removing all variable-length allocations (and adding CPPFLAG+=-Wvla at the end) is to avoid security vulnerabilities such CVE-2021-3527. > This is a performance-critical code path and BITS_TO_LONGS(nvqs) is > small. OK, having looked better at nvqs, I suppose this is preferred: -- >8 -- @@ -60,7 +60,7 @@ static void notify_guest_bh(void *opaque) { VirtIOBlockDataPlane *s = opaque; unsigned nvqs = s->conf->num_queues; - unsigned long bitmap[BITS_TO_LONGS(nvqs)]; + unsigned long bitmap[BITS_TO_LONGS(VIRTIO_QUEUE_MAX)]; unsigned j; memcpy(bitmap, s->batch_notify_vqs, sizeof(bitmap)); --- Would that work for you? > > Stefan >