RE: wmi: usercopy: Kernel memory overwrite attempt detected to spans multiple pages (offset 0, size 4104)

[<Mario.Limonciello@dell.com>]

> -----Original Message-----
> From: platform-driver-x86-owner@vger.kernel.org [mailto:platform-driver-x86-
> owner@vger.kernel.org] On Behalf Of Mihai Don?u
> Sent: Sunday, June 17, 2018 2:30 PM
> To: Kees Cook
> Cc: LKML; Darren Hart; Andy Shevchenko; Platform Driver
> Subject: Re: wmi: usercopy: Kernel memory overwrite attempt detected to spans
> multiple pages (offset 0, size 4104)
> 
> On Sun, 2018-06-17 at 10:36 -0700, Kees Cook wrote:
> > On Sat, Jun 16, 2018 at 3:04 PM, Mihai Donțu wrote:
> > > On Sun, 2018-06-17 at 00:01 +0300, Mihai Donțu wrote:
> > > > While trying to adjust the keyboard backlight mode, I hit this BUG:
> > > >
> > > > Jun 16 22:16:07 mdontu-l kernel: usercopy: Kernel memory overwrite attempt
> detected to spans multiple pages (offset 0, size 4104)!
> >
> > CONFIG_HARDENED_USERCOPY_PAGESPAN=y is really only useful for
> > debugging special cases. For now, I recommend leaving it disabled,
> > since there are a lot of cases it still trips over.
> >
> > > I eventually sprinkled some printk-s and got this:
> > >
> > >  855         if (copy_from_user(buf, input, wblock->req_buf_size)) {
> > >  856                 dev_dbg(&wblock->dev.dev, "Copy %llu from user failed\n",
> > >  857                         wblock->req_buf_size);
> > >  858                 ret = -EFAULT;
> > >  859                 goto out_ioctl;
> > >  860         }
> >
> > However, since you tracked this one down, I think this would be fixed
> > by adjusting the handler_data allocation:
> >
> >
> > diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
> > index 8e3d0146ff8c..ea6bf98f197a 100644
> > --- a/drivers/platform/x86/wmi.c
> > +++ b/drivers/platform/x86/wmi.c
> > @@ -918,8 +918,8 @@ static int wmi_dev_probe(struct device *dev)
> >                 }
> >
> >                 count = get_order(wblock->req_buf_size);
> > -               wblock->handler_data = (void *)__get_free_pages(GFP_KERNEL,
> > -                                                               count);
> > +               wblock->handler_data = (void *)
> > +                       __get_free_pages(GFP_KERNEL | __GFP_COMP, count);
> >                 if (!wblock->handler_data) {
> >                         ret = -ENOMEM;
> >                         goto probe_failure;
> >
> 
> Your patch works OK for me, thank you. The libsmbios tool, however, not
> so much. It appears to be behind latest developments.
> 
> # echo "+keyboard" >/sys/class/leds/dell\:\:kbd_backlight/start_triggers

Please feel free to send a PR to augment libsmbios to prefer this sysfs interface
if it's present over the direct communication path.

> 
> is all that is needed today.
> 
> Regards,
> 
> > But in looking further, I don't know why this is using
> > __get_free_pages() instead of kmalloc? In fact, there is a kfree() in
> > the error path, which looks wrong:
> >
> >         kfree(wblock->handler_data);
> >
> > I think this should just be converted to using kmalloc/kfree everywhere.
> 
> --
> Mihai Donțu