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

[Elliot Berman <quic_eberman@quicinc.com>]

On 3/24/2023 11:37 AM, Will Deacon wrote:
> 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@quicinc.com>
>> Signed-off-by: Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>
>> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
>> ---
>>   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.
> 

Added the accounting for the v12.

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

Userspace will get EBADADDR (-14) back when trying to launch the VM 
(pin_user_pages_fast returns this as you might have been expecting). We 
haven't yet had any need to support file-backed mappings.

Thanks,
Elliot

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