Bjorn Helgaas <[email protected]> writes:
> On Fri, Mar 11, 2016 at 03:39:18PM +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. fb_is_primary_device() is not on any performance critical
>> path, replace to_pci_dev() with raw scan.
>>
>> Signed-off-by: Vitaly Kuznetsov <[email protected]>
>> ---
>> arch/x86/video/fbdev.c | 12 +++++++++---
>> 1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/x86/video/fbdev.c b/arch/x86/video/fbdev.c
>> index d5644bb..f309d6c 100644
>> --- a/arch/x86/video/fbdev.c
>> +++ b/arch/x86/video/fbdev.c
>> @@ -14,12 +14,18 @@
>> int fb_is_primary_device(struct fb_info *info)
>> {
>> struct device *device = info->device;
>> - struct pci_dev *pci_dev = NULL;
>> + struct pci_dev *dev = NULL, *pci_dev = NULL;
>> struct pci_dev *default_device = vga_default_device();
>> struct resource *res = NULL;
>>
>> - if (device)
>> - pci_dev = to_pci_dev(device);
>> + /*
>> + * We're not sure info->device is a pci device, do full scan instead
>> + * of to_pci_dev().
>> + */
>> + for_each_pci_dev(dev) {
>> + if (&dev->dev == device)
>> + pci_dev = dev;
>> + }
>> if (!pci_dev)
>> return 0;
>
> I think dev_is_pci() is a better solution:
>
> if (!device || !dev_is_pci(device))
> return 0;
Sure, will do v2.
>
> pci_dev = to_pci_dev(device);
> if (vga_default_device()) {
> if (vga_default_device() == pci_dev)
> return 1;
> return 0;
> }
>
> res = &pci_dev->resource[PCI_ROM_RESOURCE];
> if (res->flags & IORESOURCE_ROM_SHADOW)
> return 1;
>
> return 0;
>
> This says a non-PCI device cannot be the primary device. I don't know
> framebuffers, so I don't know if that's what you really want, but I
> guess it's what the original code says.
Yes, the original code is for pci devices only and I didn't plan to
change that, my intention is to prevent out-of-bounds access.
>
> Bjorn
--
Vitaly
