[lkml]   [2018]   [May]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH v2] efi: Ignore unrealistically large option roms
On 1 May 2018 at 15:52, David Laight <> wrote:
> From: Ard Biesheuvel
>> Sent: 28 April 2018 07:41
>> On 27 April 2018 at 23:35, Hans de Goede <> 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.

16 MB is the smallest number we can use that still guarantees that we
will not misidentify a valid option ROM as bogus. But in reality,
option ROMs are rarely that large.

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

Could you elaborate?

 \ /
  Last update: 2018-05-01 15:58    [W:0.033 / U:0.304 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site