Re: [PATCH v10 13/26] gunyah: vm_mgr: Add ioctls to support basic non-proxy VM boot

[Elliot Berman]

On 2/15/2023 10:35 PM, Greg Kroah-Hartman wrote:
> On Tue, Feb 14, 2023 at 01:24:26PM -0800, Elliot Berman wrote:
> > +	case GH_VM_SET_DTB_CONFIG: {
> > +		struct gh_vm_dtb_config dtb_config;
> > +
> > +		if (copy_from_user(&dtb_config, argp, sizeof(dtb_config)))
> > +			return -EFAULT;
> > +
> > +		dtb_config.size = PAGE_ALIGN(dtb_config.size);
> > +		ghvm->dtb_config = dtb_config;
>
> Do you really mean to copy this tiny structure twice (once from
> userspace and the second time off of the stack)?  If so, why?

Ah, yes this can be optimized to copy directly.
> And where are the values of the structure checked for validity?  Can any
> 64bit value work for size and "gpa"?

The values get checked when starting the VM

static int gh_vm_start(struct gh_vm *ghvm)
	...
	mapping = gh_vm_mem_find_mapping(ghvm, ghvm->dtb_config.gpa, 
ghvm->dtb_config.size);
	if (!mapping) {
		pr_warn("Failed to find the memory_handle for DTB\n");
		ret = -EINVAL;
		goto err;
	}

If user passes an address that they've not set up, then 
gh_vm_mem_find_mapping returns NULL and GH_VM_START ioctl fails.

I've not done the check from the GH_VM_SET_DTB_CONFIG ioctl itself 
because I didn't want to require userspace to share the memory first. 
We'd need to check again anyway since user could SET_USER_MEMORY, 
SET_DTB_CONFIG, SET_USER_MEMORY (remove), VM_START.

Thanks,
Elliot