linux-kernel - Re: [PATCH v4] usb: core: setup dma_pfn_offset for USB devices and, interfaces

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4403953.WnstcHvg1n@wuerfel>
Date:   Tue, 13 Sep 2016 12:36:43 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Roger Quadros <rogerq@...com>
Cc:     gregkh@...uxfoundation.org, stern@...land.harvard.edu,
        ssantosh@...nel.org, grygorii.strashko@...com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] usb: core: setup dma_pfn_offset for USB devices and, interfaces

On Tuesday, September 13, 2016 11:16:03 AM CEST Roger Quadros wrote:
> If dma_pfn_offset is not inherited correctly from the host controller,
> it might result in sub-optimal configuration as bounce
> buffer limit might be set to less than optimal level.
> 
> Consider the mass storage device case.
> USB storage driver creates a scsi host for the mass storage interface in
> drivers/usb/storage/usb.c
> The scsi host parent device is nothing but the the USB interface device.
> Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out
> and set the block layer bounce limit.
> scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the
> bounce_limit. host_dev is nothing but the device representing the
> mass storage interface.
> If that device doesn't have the right dma_pfn_offset, then dma_max_pfn()
> is messed up and the bounce buffer limit is wrong.
> 
> e.g. On Keystone 2 systems, dma_max_pfn() is 0x87FFFF and dma_mask_pfn
> is 0xFFFFF. Consider a mass storage use case: Without this patch,
> usb scsi host device (usb-storage) will get a dma_pfn_offset of 0 resulting
> in a dma_max_pfn() of 0xFFFFF within the scsi layer
> (scsi_calculate_bounce_limit()).
> This will result in bounce buffers being unnecessarily used.
> 
> Hint: On 32-bit ARM platforms dma_max_pfn() = dma_mask_pfn + dma_pfn_offset
> 
> Signed-off-by: Roger Quadros <rogerq@...com>

Acked-by: Arnd Bergmann <arnd@...db.de>