linux-kernel - Re: [PATCH v2] x86: don't assume all fb devices are PCI devices

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Message-ID: <87io0p2egd.fsf@vitty.brq.redhat.com>
Date:	Mon, 14 Mar 2016 17:48:18 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Bjorn Helgaas <helgaas@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Cathy Avery <cavery@...hat.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>
Subject: Re: [PATCH v2] x86: don't assume all fb devices are PCI devices

Ingo Molnar <mingo@...nel.org> writes:

> * Bjorn Helgaas <helgaas@...nel.org> wrote:
>
>> On Mon, Mar 14, 2016 at 03:42:57PM +0100, Vitaly Kuznetsov wrote:
>> > When booting Hyper-V Generation 2 guests KASAN reports the following
>> > out-of-bounds access:
>> > 
>> > BUG: KASAN: slab-out-of-bounds in fb_is_primary_device+0x58/0x70 at addr
>> >   ffff880079cf0eb0
>> > Read of size 8 by task swapper/0/1
>> > ...
>> >  [<ffffffff81581308>] dump_stack+0x63/0x8b
>> >  [<ffffffff812e1f99>] print_trailer+0xf9/0x150
>> >  [<ffffffff812e7344>] object_err+0x34/0x40
>> >  [<ffffffff812e9630>] kasan_report_error+0x230/0x550
>> >  [<ffffffff812e9ee8>] kasan_report+0x58/0x60
>> >  [<ffffffff812e4500>] ? ___slab_alloc+0x80/0x490
>> >  [<ffffffff81878a28>] ? fb_is_primary_device+0x58/0x70
>> >  [<ffffffff812e87cd>] __asan_load8+0x5d/0x70
>> >  [<ffffffff81878a28>] fb_is_primary_device+0x58/0x70
>> >  [<ffffffff8162357a>] register_framebuffer+0xda/0x5b0
>> >  [<ffffffff816234a0>] ? remove_conflicting_framebuffers+0x50/0x50
>> > ...
>> > 
>> > The issue is caused by the to_pci_dev() call with no check that the given
>> > info->device is in fact a pci device and some fb devices (Hyper-V FB, EFI
>> > FB,...) are not.
>> > 
>> > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> 
>> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>> 
>> > ---
>> > Changes since v1: use dev_is_pci() instead of full scan [Bjorn Helgaas].
>> > ---
>> >  arch/x86/video/fbdev.c | 7 +++----
>> >  1 file changed, 3 insertions(+), 4 deletions(-)
>> > 
>> > diff --git a/arch/x86/video/fbdev.c b/arch/x86/video/fbdev.c
>> > index d5644bb..9f2fe63 100644
>> > --- a/arch/x86/video/fbdev.c
>> > +++ b/arch/x86/video/fbdev.c
>> > @@ -18,12 +18,11 @@ int fb_is_primary_device(struct fb_info *info)
>> >  	struct pci_dev *default_device = vga_default_device();
>> >  	struct resource *res = NULL;
>> 
>> The initializations of "pci_dev" and "res" to NULL are now
>> unnecessary.
>> 
>> >  
>> > -	if (device)
>> > -		pci_dev = to_pci_dev(device);
>> > -
>> > -	if (!pci_dev)
>> > +	if (!device || !dev_is_pci(device))
>> >  		return 0;
>> >  
>> > +	pci_dev = to_pci_dev(device);
>> > +
>> >  	if (default_device) {
>> >  		if (pci_dev == default_device)
>> >  			return 1;
>> 
>> The test for non-NULL "res" below is superfluous because we know
>> "pci_dev" is non-NULL:
>> 
>>   res = &pci_dev->resource[PCI_ROM_RESOURCE];
>>   if (res && res->flags & IORESOURCE_ROM_SHADOW)
>> 
>> I think your patch is functionally correct, so it's up to you and the
>> x86 guys whether you want to do these additional cleanups.
>
> I'd like to see those cleanups as well, no point in delaying them, right?
>

Sure, will do v3!

> btw., I'd suggest writing this:
>
>>   res = &pci_dev->resource[PCI_ROM_RESOURCE];
>
> as:
>
>>   res = pci_dev->resource + PCI_ROM_RESOURCE;
>

-- 
  Vitaly