Remove WARN_ONCE for unaligned UEFI region?

[Heinrich Schuchardt]

On 11/5/22 23:43, Ard Biesheuvel wrote:
> On Sat, 5 Nov 2022 at 22:54, Ard Biesheuvel <ardb at kernel.org> wrote:
>>
>> (cc Heinrich and Ilias)
>>
>> On Sat, 5 Nov 2022 at 21:27, Linus Torvalds
>> <torvalds at linux-foundation.org> wrote:
>>>
>>> On Sat, Nov 5, 2022 at 1:18 PM Ard Biesheuvel <ardb at kernel.org> wrote:
>>>>
>>>> Yeah just rip it out. In the beginning, we tended to make these
>>>> warnings noisy so people will actually notice.
>>>
>>> Rip it out entirely, or replace ith pr_warn_once()?
>>>
>>
>> A warning that can only trigger on 16k or 64k page size kernels
>> clearly doesn't have a lot of coverage, so either we just drop it, or
>> we make the warning use SZ_64K and not PAGE_SIZE.
>>
>> And if we keep the warning, it should be separate from the if(): when
>> the regions are misaligned, we have to use RWX mappings because an
>> adjacent region that gets covered by the same mapping might require
>> it.
>>
>> Maybe I'll just whip up a patch myself.
>>
>>>> I'd still like to see a memory map (boot with efi=debug) so we can get
>>>> this reported and fixed in uboot. We need that so 16k and 64k pages
>>>> boot doesn't cause surprises with overlapping mappings.
>>>
>>> Here's the dmesg attached with efi=debug for your viewing pleasure.
>>>
>>
>> Thanks.
>>
>> I've cc'ed the u-boot EFI maintainers, who take EFI spec compliance
>> very seriously, so I'm sure we'll get this fixed quickly.
> 
> Grrr looking at the spec, it seems the wording we proposed at the time
> never made it in, and at the moment, it just reads:

Could you, please, provide a link to the proposal.

Best regards

Heinrich

> 
> """
> If a 64KiB physical page contains any 4KiB page with any of the
> following types listed below, then all 4KiB pages in the 64KiB page
> must use identical ARM Memory Page Attributes:
> — EfiRuntimeServicesCode
> — EfiRuntimeServicesData
> ...
> """
> 
> The problem here is that it doesn't take permission attributes into
> account, allowing the firmware to cram code and data regions into the
> same 64k page, and instructing the OS to use R-X for the code and RW-
> for the data, which it cannot do if it uses 16k or 64k pages.
> 
> So let's drop the warning and add it back later once the spec actually
> supports it.
> 
> Patch on its way ...