linux-kernel - Re: [PATCH] usb: gadget: dummy_hcd: execute hrtimer callback in softirq context

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Message-ID: <2024090332-whomever-careless-5b7d@gregkh>
Date: Tue, 3 Sep 2024 09:09:53 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: Alan Stern <stern@...land.harvard.edu>,
	Marcello Sylvester Bauer <sylv@...v.io>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Aleksandr Nogikh <nogikh@...gle.com>,
	Marco Elver <elver@...gle.com>,
	Alexander Potapenko <glider@...gle.com>, kasan-dev@...glegroups.com,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+2388cdaeb6b10f0c13ac@...kaller.appspotmail.com,
	syzbot+17ca2339e34a1d863aad@...kaller.appspotmail.com,
	stable@...r.kernel.org, andrey.konovalov@...ux.dev
Subject: Re: [PATCH] usb: gadget: dummy_hcd: execute hrtimer callback in
 softirq context

On Tue, Aug 27, 2024 at 02:02:00AM +0200, Andrey Konovalov wrote:
> On Mon, Jul 29, 2024 at 4:23 AM <andrey.konovalov@...ux.dev> wrote:
> >
> > From: Andrey Konovalov <andreyknvl@...il.com>
> >
> > Commit a7f3813e589f ("usb: gadget: dummy_hcd: Switch to hrtimer transfer
> > scheduler") switched dummy_hcd to use hrtimer and made the timer's
> > callback be executed in the hardirq context.
> >
> > With that change, __usb_hcd_giveback_urb now gets executed in the hardirq
> > context, which causes problems for KCOV and KMSAN.
> >
> > One problem is that KCOV now is unable to collect coverage from
> > the USB code that gets executed from the dummy_hcd's timer callback,
> > as KCOV cannot collect coverage in the hardirq context.
> >
> > Another problem is that the dummy_hcd hrtimer might get triggered in the
> > middle of a softirq with KCOV remote coverage collection enabled, and that
> > causes a WARNING in KCOV, as reported by syzbot. (I sent a separate patch
> > to shut down this WARNING, but that doesn't fix the other two issues.)
> >
> > Finally, KMSAN appears to ignore tracking memory copying operations
> > that happen in the hardirq context, which causes false positive
> > kernel-infoleaks, as reported by syzbot.
> >
> > Change the hrtimer in dummy_hcd to execute the callback in the softirq
> > context.
> >
> > Reported-by: syzbot+2388cdaeb6b10f0c13ac@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=2388cdaeb6b10f0c13ac
> > Reported-by: syzbot+17ca2339e34a1d863aad@...kaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=17ca2339e34a1d863aad
> > Fixes: a7f3813e589f ("usb: gadget: dummy_hcd: Switch to hrtimer transfer scheduler")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>
> 
> Hi Greg,
> 
> Could you pick up either this or Marcello's patch
> (https://lkml.org/lkml/2024/6/26/969)? In case they got lost.

Both are lost now, (and please use lore.kernel.org, not lkml.org), can
you resend the one that you wish to see accepted?

thanks,

greg k-h