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Sun, 18 Oct 2026 14:43:21 -0700 (PDT) Date: Sun, 18 Oct 2026 17:43:19 -0400 From: "Michael S. Tsirkin" To: Linus Torvalds Cc: Haoran Wang , jasowangio@gmail.com, kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, eperezma@redhat.com, linux-kernel@vger.kernel.org, security@kernel.org Subject: Re: [BUG] vhost/vringh: __get_user without access_ok leaks kernel memory via vDPA passthrough Message-ID: <20261018174250-mutt-send-email-mst@kernel.org> References: <6ad07f8a.a0c71a5e.2d2efd.977a@mx.google.com> <20261018152358-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sun, Oct 18, 2026 at 10:34:12AM -1000, Linus Torvalds wrote: > On Sun, 18 Oct 2026 at 09:26, Michael S. Tsirkin wrote: > > > > + __virtio16 __user *uaddr = ivec.iov.iovec[0].iov_base; > > + > > + if (!access_ok(uaddr, sizeof(*p))) > > + return -EFAULT; > > + ret = __get_user(tmp, uaddr); > > You should never use __get_user() in the first place. It is almost > always just a bug. Right, I was thinking of some other code. This one should just be get_user. > And __get_user() together with access_ok() is actively wrong and > stupid. It's slower, bigger, and more bug-prone than just using > "get_user()". > > The *only* reason ever to use __get_user() is in very very iffy code > that might use a kernel pointer and doesn't want the access_ok() code. > > Or old legacy code from the last century when __get_user() was faster > and was inlined. > > Linus