linux-kernel - Re: [PATCH v3 2/7] firmware: coreboot: Unmap ioregion on failure

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Date:   Thu, 09 Aug 2018 12:40:31 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org,
        Wei-Ning Huang <wnhuang@...omium.org>,
        Julius Werner <jwerner@...omium.org>,
        Samuel Holland <samuel@...lland.org>
Subject: Re: [PATCH v3 2/7] firmware: coreboot: Unmap ioregion on failure

Quoting Brian Norris (2018-08-09 10:49:38)
> On Thu, Aug 09, 2018 at 10:17:17AM -0700, Stephen Boyd wrote:
> > Both callers of coreboot_table_init() ioremap the pointer that comes in
> > but they don't unmap the memory on failure. Both of them also fail probe
> > immediately with the return value of coreboot_table_init(), leaking a
> > mapping when it fails. Plug the leak so the mapping isn't left unused.
> > 
> > Cc: Wei-Ning Huang <wnhuang@...omium.org>
> > Cc: Julius Werner <jwerner@...omium.org>
> > Cc: Brian Norris <briannorris@...omium.org>
> > Cc: Samuel Holland <samuel@...lland.org>
> > Fixes: 570d30c2823f ("firmware: coreboot: Expose the coreboot table as a bus")
> 
> I suppose this is fair, since that commit introduced error paths and
> didn't clean them up. But one warning below:
> 
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> > ---
> >  drivers/firmware/google/coreboot_table.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
> > index 19db5709ae28..0d3e140444ae 100644
> > --- a/drivers/firmware/google/coreboot_table.c
> > +++ b/drivers/firmware/google/coreboot_table.c
> > @@ -138,6 +138,9 @@ int coreboot_table_init(struct device *dev, void __iomem *ptr)
> >               ptr_entry += entry.size;
> >       }
> >  
> > +     if (ret)
> > +             iounmap(ptr);
> 
> This works because no sub-driver is using this mapping any more (i.e.,
> because we killed coreboot_table_find()). Otherwise, we'd need to
> explicitly kill all the sub-devices first. IOW, if this gets backported
> to older kernels, it would need to go along with this and its other
> dependencies:

The memory is copied out of the table. So do the devices actually use
the memory that we remap here? I don't see how it's a problem if we
unmap the table after we populate devices.

> 
> b616cf53aa7a firmware: coreboot: Remove unused coreboot_table_find
> 
> But I guess that's a question for -stable. Or, we remove the 'Fixes'
> tag? Or add another tag, to list other dependencies? Or just ignore it.
> 
> But for this change as applied to mainline:
> 
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> 

Thanks!