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[79.176.51.222]) by smtp.gmail.com with ESMTPSA id d6sm27113086wrw.10.2020.04.06.08.35.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 08:35:27 -0700 (PDT) Date: Mon, 6 Apr 2020 11:35:26 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org Subject: [PATCH v2 2/2] vhost: force spec specified alignment on types Message-ID: <20200406153245.127680-3-mst@redhat.com> References: <20200406153245.127680-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200406153245.127680-1-mst@redhat.com> X-Mailer: git-send-email 2.24.1.751.gd10ce2899c X-Mutt-Fcc: =sent Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The ring element addresses are passed between components with different alignments assumptions. Thus, if guest/userspace selects a pointer and host then gets and dereferences it, we might need to decrease the compiler-selected alignment to prevent compiler on the host from assuming pointer is aligned. This actually triggers on ARM with -mabi=apcs-gnu - which is a deprecated configuration, but it seems safer to handle this generally. I verified that the produced binary is exactly identical on x86. Signed-off-by: Michael S. Tsirkin --- drivers/vhost/vhost.h | 6 +++--- include/linux/virtio_ring.h | 24 +++++++++++++++++++++--- 2 files changed, 24 insertions(+), 6 deletions(-) diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index cc82918158d2..a67bda9792ec 100644 --- a/drivers/vhost/vhost.h +++ b/drivers/vhost/vhost.h @@ -74,9 +74,9 @@ struct vhost_virtqueue { /* The actual ring of buffers. */ struct mutex mutex; unsigned int num; - struct vring_desc __user *desc; - struct vring_avail __user *avail; - struct vring_used __user *used; + vring_desc_t __user *desc; + vring_avail_t __user *avail; + vring_used_t __user *used; const struct vhost_iotlb_map *meta_iotlb[VHOST_NUM_ADDRS]; struct vhost_desc *descs; diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h index 09fc6164b523..efcb9fde1dbf 100644 --- a/include/linux/virtio_ring.h +++ b/include/linux/virtio_ring.h @@ -113,14 +113,32 @@ void vring_transport_features(struct virtio_device *vdev); irqreturn_t vring_interrupt(int irq, void *_vq); +/* + * The ring element addresses are passed between components with different + * alignments assumptions. Thus, we might need to decrease the compiler-selected + * alignment, and so must use a typedef to make sure the __aligned attribute + * actually takes hold: + * + * https://gcc.gnu.org/onlinedocs//gcc/Common-Type-Attributes.html#Common-Type-Attributes + * + * When used on a struct, or struct member, the aligned attribute can only + * increase the alignment; in order to decrease it, the packed attribute must + * be specified as well. When used as part of a typedef, the aligned attribute + * can both increase and decrease alignment, and specifying the packed + * attribute generates a warning. + */ +typedef struct vring_desc __aligned(VRING_DESC_ALIGN_SIZE) vring_desc_t; +typedef struct vring_avail __aligned(VRING_AVAIL_ALIGN_SIZE) vring_avail_t; +typedef struct vring_used __aligned(VRING_USED_ALIGN_SIZE) vring_used_t; + struct vring_s { unsigned int num; - struct vring_desc *desc; + vring_desc_t *desc; - struct vring_avail *avail; + vring_avail_t *avail; - struct vring_used *used; + vring_used_t *used; }; static inline void vring_legacy_init(struct vring_s *vr, unsigned int num, void *p, -- MST