On Thu, Nov 19, 2020 at 10:59:19AM -0800, Tom Roeder wrote: > This patch changes the NVMe PCI implementation to cache host_mem_descs > in non-DMA memory instead of depending on descriptors stored in DMA > memory. This change is needed under the malicious-hypervisor threat > model assumed by the AMD SEV and Intel TDX architectures, which encrypt > guest memory to make it unreadable. Some versions of these architectures > also make it cryptographically hard to modify guest memory without > detection. > > On these architectures, Linux generally leaves DMA memory unencrypted so > that devices can still communicate directly with the kernel: DMA memory > remains readable to and modifiable by devices. This means that this > memory is also accessible to a hypervisor. > > However, this means that a malicious hypervisor could modify the addr or > size fields of descriptors and cause the NVMe driver to call > dma_free_attrs on arbitrary addresses or on the right addresses but with > the wrong size. To prevent this attack, this commit changes the code to > cache those descriptors in non-DMA memory and to use the cached values > when freeing the memory they describe. If the hypervisor does that, then the device may use the wrong addresses, too. I guess you can't do anything about that from the driver, though.
> + /* Cache the host_mem_descs in non-DMA memory so a malicious hypervisor > + * can't change them. > + */ > + struct nvme_host_mem_buf_desc *host_mem_descs_cache; > void **host_mem_desc_bufs; This is never seen by an nvme device, so no need for an nvme specific type here. You can use arch native types.
