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([2001:b07:6468:f312:29ed:810e:962c:aa0d]) by smtp.gmail.com with ESMTPSA id x18sm9252844wmi.35.2020.06.12.09.51.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 12 Jun 2020 09:51:19 -0700 (PDT) Subject: Re: [PATCH] memory: Revert "memory: accept mismatching sizes in memory_region_access_valid" To: "Michael S. Tsirkin" , qemu-devel@nongnu.org References: <20200610134731.1514409-1-mst@redhat.com> From: Paolo Bonzini Message-ID: <3c7ba098-b059-c825-a46d-8ba1c7896eab@redhat.com> Date: Fri, 12 Jun 2020 18:51:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200610134731.1514409-1-mst@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/12 08:07:17 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: qemu-stable@nongnu.org, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/06/20 15:47, Michael S. Tsirkin wrote: > Memory API documentation documents valid .min_access_size and .max_access_size > fields and explains that any access outside these boundaries is blocked. > > This is what devices seem to assume. > > However this is not what the implementation does: it simply > ignores the boundaries unless there's an "accepts" callback. > > Naturally, this breaks a bunch of devices. > > Revert to the documented behaviour. > > Devices that want to allow any access can just drop the valid field, > or add the impl field to have accesses converted to appropriate > length. > > Cc: qemu-stable@nongnu.org > Reviewed-by: Richard Henderson > Fixes: CVE-2020-13754 > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1842363 > Fixes: a014ed07bd5a ("memory: accept mismatching sizes in memory_region_access_valid") > Signed-off-by: Michael S. Tsirkin > --- > memory.c | 29 +++++++++-------------------- > 1 file changed, 9 insertions(+), 20 deletions(-) > > diff --git a/memory.c b/memory.c > index 91ceaf9fcf..3e9388fb74 100644 > --- a/memory.c > +++ b/memory.c > @@ -1352,35 +1352,24 @@ bool memory_region_access_valid(MemoryRegion *mr, > bool is_write, > MemTxAttrs attrs) > { > - int access_size_min, access_size_max; > - int access_size, i; > + if (mr->ops->valid.accepts > + && !mr->ops->valid.accepts(mr->opaque, addr, size, is_write, attrs)) { > + return false; > + } > > if (!mr->ops->valid.unaligned && (addr & (size - 1))) { > return false; > } > > - if (!mr->ops->valid.accepts) { > + /* Treat zero as compatibility all valid */ > + if (!mr->ops->valid.max_access_size) { > return true; > } > > - access_size_min = mr->ops->valid.min_access_size; > - if (!mr->ops->valid.min_access_size) { > - access_size_min = 1; > + if (size > mr->ops->valid.max_access_size > + || size < mr->ops->valid.min_access_size) { > + return false; > } > - > - access_size_max = mr->ops->valid.max_access_size; > - if (!mr->ops->valid.max_access_size) { > - access_size_max = 4; > - } > - > - access_size = MAX(MIN(size, access_size_max), access_size_min); > - for (i = 0; i < size; i += access_size) { > - if (!mr->ops->valid.accepts(mr->opaque, addr + i, access_size, > - is_write, attrs)) { > - return false; > - } > - } > - > return true; > } > > Queued, thanks. Paolo