From mboxrd@z Thu Jan  1 00:00:00 1970
From: vinod.koul@intel.com (Vinod Koul)
Date: Tue, 4 Oct 2016 21:06:45 +0530
Subject: [PATCH] dmaengine: coh901318: fix integer overflow when shifting
 more than 32 places
In-Reply-To: <CACRpkdZ1gfZu=Snh9YK1X9w+ZW-zcuEFh8aojGi-LUKoyMKcCQ@mail.gmail.com>
References: <20160929175725.14157-1-colin.king@canonical.com>
 <1475172392.2027.12.camel@perches.com>
 <CACRpkdZ1gfZu=Snh9YK1X9w+ZW-zcuEFh8aojGi-LUKoyMKcCQ@mail.gmail.com>
Message-ID: <20161004153645.GG2467@localhost>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Oct 04, 2016 at 02:23:51PM +0200, Linus Walleij wrote:
> On Thu, Sep 29, 2016 at 8:06 PM, Joe Perches <joe@perches.com> wrote:
> > On Thu, 2016-09-29 at 18:57 +0100, Colin King wrote:
> >> Currently U300_DMA_CHANNELS is set to 40, meaning that the shift of 1 can
> >> be more than 32 places, which leads to a 32 bit integer overflow. Fix this
> >> by casting 1 to a u64 (the same type as started_channels) before shifting
> >> it.
> >
> > trivia:
> >
> >> diff --git a/drivers/dma/coh901318.c b/drivers/dma/coh901318.c
> > []
> >> @@ -1353,7 +1353,7 @@ static ssize_t coh901318_debugfs_read(struct file *file, char __user *buf,
> >>       tmp += sprintf(tmp, "DMA -- enabled dma channels\n");
> >>
> >>       for (i = 0; i < U300_DMA_CHANNELS; i++)
> >> -             if (started_channels & (1 << i))
> >> +             if (started_channels & ((u64)1 << i))
> >
> > Using
> >
> >                 if (started_channels & (1ULL << i))
> >
> > would be more common.
> 
> Even better (IMO):
> 
> #include <linux/bitops.h>
> 
> if (started_channels & BIT(i))
> 
> Apparently code is there to avoid the bit 31 problem, mea culpa.

I have already applied this one, so feel free to send this as an update :)

-- 
~Vinod