linux-kernel - Re: Validating dma_mmap_coherent() parameters before calling (was Re: WARNING in memtype

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Date:   Thu, 14 May 2020 13:22:00 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     Christoph Hellwig <hch@....de>, Hillf Danton <hdanton@...a.com>,
        syzbot <syzbot+353be47c9ce21b68b7ed@...kaller.appspotmail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, x86@...nel.org
Subject: Re: Validating dma_mmap_coherent() parameters before calling (was
 Re: WARNING in memtype_reserve)

On Thu, May 14, 2020 at 06:17:41AM -0500, Jeremy Linton wrote:
> 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, I'll turn this into a "real" patch now...

greg k-h