Re: [PATCH v2 1/4] usb: usbfs: Enforce page requirements for mmap

From: Alan Stern
Date: Mon May 15 2023 - 10:07:31 EST

On Mon, May 15, 2023 at 09:09:55PM +0800, Ruihan Li wrote:
> The current implementation of usbdev_mmap uses usb_alloc_coherent to
> allocate memory pages that will later be mapped into the user space.
> Meanwhile, usb_alloc_coherent employs three different methods to
> allocate memory, as outlined below:
> * If hcd->localmem_pool is non-null, it uses gen_pool_dma_alloc to
> allocate memory;
> * If DMA is not available, it uses kmalloc to allocate memory;
> * Otherwise, it uses dma_alloc_coherent.
> However, it should be noted that gen_pool_dma_alloc does not guarantee
> that the resulting memory will be page-aligned. Furthermore, trying to
> map slab pages (i.e., memory allocated by kmalloc) into the user space
> is not resonable and can lead to problems, such as a type confusion bug
> when PAGE_TABLE_CHECK=y [1].
> To address these issues, this patch introduces hcd_alloc_coherent_pages,
> which addresses the above two problems. Specifically,
> hcd_alloc_coherent_pages uses gen_pool_dma_alloc_align instead of
> gen_pool_dma_alloc to ensure that the memory is page-aligned. To replace
> kmalloc, hcd_alloc_coherent_pages directly allocates pages by calling
> __get_free_pages.
> Reported-by: syzbot+fcf1a817ceb50935ce99@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: [1]
> Fixes: f7d34b445abc ("USB: Add support for usbfs zerocopy.")
> Fixes: ff2437befd8f ("usb: host: Fix excessive alignment restriction for local memory allocations")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ruihan Li <lrh2000@xxxxxxxxxx>
> ---

For parts 1/4 and 2/4:

Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

Alan Stern