Re: [PATCH v11 12/26] gunyah: vm_mgr: Add/remove user memory regions

[Will Deacon]

On Fri, Mar 03, 2023 at 05:06:18PM -0800, Elliot Berman wrote:
> When launching a virtual machine, Gunyah userspace allocates memory for
> the guest and informs Gunyah about these memory regions through
> SET_USER_MEMORY_REGION ioctl.
> 
> Co-developed-by: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@xxxxxxxxxxx>
> Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
> ---
>  drivers/virt/gunyah/Makefile    |   2 +-
>  drivers/virt/gunyah/vm_mgr.c    |  44 ++++++
>  drivers/virt/gunyah/vm_mgr.h    |  25 ++++
>  drivers/virt/gunyah/vm_mgr_mm.c | 229 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/gunyah.h     |  29 ++++
>  5 files changed, 328 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/virt/gunyah/vm_mgr_mm.c

[...]

> +int gh_vm_mem_alloc(struct gh_vm *ghvm, struct gh_userspace_memory_region *region)
> +{
> +	struct gh_vm_mem *mapping, *tmp_mapping;
> +	struct gh_rm_mem_entry *mem_entries;
> +	phys_addr_t curr_page, prev_page;
> +	struct gh_rm_mem_parcel *parcel;
> +	int i, j, pinned, ret = 0;
> +	size_t entry_size;
> +	u16 vmid;
> +
> +	if (!region->memory_size || !PAGE_ALIGNED(region->memory_size) ||
> +		!PAGE_ALIGNED(region->userspace_addr) || !PAGE_ALIGNED(region->guest_phys_addr))
> +		return -EINVAL;
> +
> +	if (region->guest_phys_addr + region->memory_size < region->guest_phys_addr)
> +		return -EOVERFLOW;
> +
> +	ret = mutex_lock_interruptible(&ghvm->mm_lock);
> +	if (ret)
> +		return ret;
> +
> +	mapping = __gh_vm_mem_find_by_label(ghvm, region->label);
> +	if (mapping) {
> +		mutex_unlock(&ghvm->mm_lock);
> +		return -EEXIST;
> +	}
> +
> +	mapping = kzalloc(sizeof(*mapping), GFP_KERNEL);
> +	if (!mapping) {
> +		mutex_unlock(&ghvm->mm_lock);
> +		return -ENOMEM;
> +	}
> +
> +	mapping->parcel.label = region->label;
> +	mapping->guest_phys_addr = region->guest_phys_addr;
> +	mapping->npages = region->memory_size >> PAGE_SHIFT;
> +	parcel = &mapping->parcel;
> +	parcel->mem_handle = GH_MEM_HANDLE_INVAL; /* to be filled later by mem_share/mem_lend */
> +	parcel->mem_type = GH_RM_MEM_TYPE_NORMAL;
> +
> +	/* Check for overlap */
> +	list_for_each_entry(tmp_mapping, &ghvm->memory_mappings, list) {
> +		if (!((mapping->guest_phys_addr + (mapping->npages << PAGE_SHIFT) <=
> +			tmp_mapping->guest_phys_addr) ||
> +			(mapping->guest_phys_addr >=
> +			tmp_mapping->guest_phys_addr + (tmp_mapping->npages << PAGE_SHIFT)))) {
> +			ret = -EEXIST;
> +			goto free_mapping;
> +		}
> +	}
> +
> +	list_add(&mapping->list, &ghvm->memory_mappings);
> +
> +	mapping->pages = kcalloc(mapping->npages, sizeof(*mapping->pages), GFP_KERNEL);
> +	if (!mapping->pages) {
> +		ret = -ENOMEM;
> +		mapping->npages = 0; /* update npages for reclaim */
> +		goto reclaim;
> +	}
> +
> +	pinned = pin_user_pages_fast(region->userspace_addr, mapping->npages,
> +					FOLL_WRITE | FOLL_LONGTERM, mapping->pages);
> +	if (pinned < 0) {
> +		ret = pinned;
> +		mapping->npages = 0; /* update npages for reclaim */
> +		goto reclaim;
> +	} else if (pinned != mapping->npages) {
> +		ret = -EFAULT;
> +		mapping->npages = pinned; /* update npages for reclaim */
> +		goto reclaim;
> +	}

I think Fuad mentioned this on an older version of these patches, but it
looks like you're failing to account for the pinned memory here which is
a security issue depending on who is able to issue the ioctl() calling
into here.

Specifically, I'm thinking that your kXalloc() calls should be using
GFP_KERNEL_ACCOUNT in this function and also that you should be calling
account_locked_vm() for the pages being pinned.

Finally, what happens if userspace passes in a file mapping?

Will