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Tue, 31 Mar 2020 14:46:47 +0000 (UTC) Received: from maximlenovopc.usersys.redhat.com (unknown [10.35.206.223]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2B6D760BEC; Tue, 31 Mar 2020 14:46:44 +0000 (UTC) Message-ID: <75f5b9944628f08554afa40d7762f91ef8f06716.camel@redhat.com> Subject: Re: [PATCH v6 07/42] nvme: refactor nvme_addr_read From: Maxim Levitsky To: Klaus Birkelund Jensen Date: Tue, 31 Mar 2020 17:46:43 +0300 In-Reply-To: <20200331124847.wbax7webzl4grv6f@apples.localdomain> References: <20200316142928.153431-1-its@irrelevant.dk> <20200316142928.153431-8-its@irrelevant.dk> <1fb18481dfcfa17c2395f3bcded0aef787badfc7.camel@redhat.com> <20200331053948.ompv75njpyhlti7i@apples.localdomain> <20200331124847.wbax7webzl4grv6f@apples.localdomain> Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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 , Beata Michalska , qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , Keith Busch , Javier Gonzalez Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, 2020-03-31 at 14:48 +0200, Klaus Birkelund Jensen wrote: > On Mar 31 13:41, Maxim Levitsky wrote: > > On Tue, 2020-03-31 at 07:39 +0200, Klaus Birkelund Jensen wrote: > > > On Mar 25 12:38, Maxim Levitsky wrote: > > > > Note that this patch still contains a bug that it removes the check against the accessed > > > > size, which you fix in later patch. > > > > I prefer to not add a bug in first place > > > > However if you have a reason for this, I won't mind. > > > > > > > > > > So yeah. The resons is that there is actually no bug at this point > > > because the controller only supports PRPs. I actually thought there was > > > a bug as well and reported it to qemu-security some months ago as a > > > potential out of bounds access. I was then schooled by Keith on how PRPs > > > work ;) Below is a paraphrased version of Keiths analysis. > > > > > > The PRPs does not cross page boundaries: > > > > True > > > > > > > > trans_len = n->page_size - (prp1 % n->page_size); > > > > > > The PRPs are always verified to be page aligned: > > > > True > > > > > > if (unlikely(!prp_ent || prp_ent & (n->page_size - 1))) { > > > > > > and the transfer length wont go above page size. So, since the beginning > > > of the address is within the CMB and considering that the CMB is of an > > > MB aligned and sized granularity, then we can never cross outside it > > > with PRPs. > > > > I understand now, however the reason I am arguing about this is > > that this patch actually _removes_ the size bound check > > > > It was before the patch: > > > > n->cmbsz && addr >= n->ctrl_mem.addr && > > addr < (n->ctrl_mem.addr + int128_get64(n->ctrl_mem.size) > > > > I don't think it does - the check is just moved to nvme_addr_is_cmb: > > static inline bool nvme_addr_is_cmb(NvmeCtrl *n, hwaddr addr) > { > hwaddr low = n->ctrl_mem.addr; > hwaddr hi = n->ctrl_mem.addr + int128_get64(n->ctrl_mem.size); > > return addr >= low && addr < hi; > } > > We check that `addr` is less than `hi`. Maybe the name is unfortunate... > > Oh, I am just blind! sorry about that. You are 100% right. Best regards, Maxim Levitsky