Re: Validating dma_mmap_coherent() parameters before calling (was Re: WARNING in memtype_reserve)

[Jeremy Linton <jeremy.linton@arm.com>]

On 5/14/20 2:46 AM, Greg KH wrote:
> On Thu, May 14, 2020 at 08:31:58AM +0200, Christoph Hellwig wrote:
>> On Thu, May 14, 2020 at 08:27:50AM +0200, Greg KH wrote:
>>> On Thu, May 14, 2020 at 08:14:17AM +0200, Christoph Hellwig wrote:
>>>> Guys, can you please start formal thread on this?  I have no
>>>> idea where this came from and what the rationale is.  Btw, if the
>>>> pfn is crap in dma_direct_mmap then the dma_addr_t passed in is
>>>> crap, as it is derived from that.  What is the caller, and how is
>>>> this triggered?
>>>
>>>
>>> Ok, to summarize, commit 2bef9aed6f0e ("usb: usbfs: correct kernel->user
>>> page attribute mismatch") changed a call from remap_pfn_range() to
>>> dma_mmap_coherent() for usb data buffers being sent from userspace.
>>
>> I only need to look at the commit for 3 seconds to tell you that it is
>> completely buggy.  While using dma_mmap_coherent is fundamentally the
>> right thing and absolutely required for dma_alloc_* allocations, USB
>> also uses it's own local gen pool allocator or plain kmalloc for not
>> DMA capable controller.  This need to use remap_pfn_range.  I'm pretty
>> sure you hit one of those cases.
>>
>> The logic should be something like:
>>
>> 	if (hcd->localmem_pool || !hcd_uses_dma(hcd))
>> 		remap_pfn_range()
>> 	else
>> 		dma_mmap_coherent()
> 
> Ok, that's simple enough, patch is below.
> 
> Jeremy, any objection to this change?

No, thats fine but since I just translated usb_alloc_coherent() to 
dma_map_coherent in my not fully away head. Putting this as 
"usb_map_cohernet()" sort of makes more sense.


> 
> thanks,
> 
> greg k-h
> 
> 
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index b9db9812d6c5..d93d94d7ff50 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -251,9 +251,19 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
>   	usbm->vma_use_count = 1;
>   	INIT_LIST_HEAD(&usbm->memlist);
>   
> -	if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle, size)) {
> -		dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
> -		return -EAGAIN;
> +	if (hcd->localmem_pool || !hcd_uses_dma(hcd)) {
> +		if (remap_pfn_range(vma, vma->vm_start,
> +				    virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> +				    size, vma->vm_page_prot) < 0) {
> +			dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
> +			return -EAGAIN;
> +		}
> +	} else {
> +		if (dma_mmap_coherent(hcd->self.sysdev, vma, mem, dma_handle,
> +				      size)) {
> +			dec_usb_memory_use_count(usbm, &usbm->vma_use_count);
> +			return -EAGAIN;
> +		}
>   	}
>   
>   	vma->vm_flags |= VM_IO;
>