RE: [PATCH v2] efi: Ignore unrealistically large option roms

[David Laight]

From: Ard Biesheuvel
> Sent: 28 April 2018 07:41
> On 27 April 2018 at 23:35, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > setup_efi_pci() tries to save a copy of each PCI option ROM as this may
> > be necessary for the device driver for the PCI device to have access too.
> >
> > On some systems the efi_pci_io_protocol_64's romimage and romsize fields
> > contain invalid data, which looks a bit like pointers pointing back into
> > other EFI code or data. Interpreting these pointers as romsize leads to
> > a very large value and if we then try to alloc this amount of memory to
> > save a copy the alloc call fails.
> >
> > This leads to a "Failed to alloc mem for rom" error being printed on the
> > EFI console for each PCI device.
> >
> > This commit avoids the printing of these errors, by checking romsize
> > before doing the alloc and if it is larger then 256M silently ignore the
> > ROM fields instead of trying to alloc mem and fail.
> >
> 
> The UEFI spec limits the size of option ROMs to 16 MiB, so I'd prefer
> we use that as the upper bound instead.

Copying even 16MB of rom data into physical memory on the 'off chance' that
the kernel might need it seems a waste of memory.

I can't help feeling that some kind of caching would be more appropriate.

	David