[U-Boot] [PATCH] efi_loader: Patch non-runtime code out at ExitBootServices already

[Heinrich Schuchardt]

On 1/25/19 10:43 PM, Ard Biesheuvel wrote:
> On Fri, 25 Jan 2019 at 19:21, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>>
>> On 1/23/19 6:33 PM, Alexander Graf wrote:
>>> While discussing something compeltely different, Ard pointed out
>>> that it might be legal to omit calling SetVirtualAddressMap altogether.
>>>
>>> While that sounds great, we currently rely on that call to remove
>>> all function pointers to code that we do not support outside of
>>> boot services.
>>>
>>> So let's patch out those bits already on the call to ExitBootServices,
>>> so that we can successfully run even when an OS chooses to omit
>>> any call to SetVirtualAddressMap.
>>
>> Such an operating system would not be allowed to use any virtual
>> addresses at any time because runtime drivers would not be informed
>> about the mapping.
>>
> 
> No. The OS would be permitted to invoke the runtime services at their
> original offset.
> 
> For arm64, this is trivially achievable, since we already use userland
> mappings for the runtime services. On 32-bit architectures, it is more
> complicated, since the boot time mapping of peripherals and/or memory
> may conflict with the kernel's layout of the address space (e.g., if
> your NOR flash lives above 0xc0000000, you *have* to remap it for the
> runtime services to be able to use it).
> 
> 
> 
>> Does such an operating system exist?
>> Or is this only a hypothetical case?
>>
>>>
>>> Reported-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>>> Signed-off-by: Alexander Graf <agraf at suse.de>
>>
>> I am missing a description of the side effects of the change, e.g.
>>
>> Our EFI unit tests call the Reset() service.
>>
>> So Python tests will fail on systems that do not implement Reset() in a
>> runtime compatible manner.
>>
> 
> All runtime services (except SetVirtualAddresMap() and
> ConvertPointer(), obviously) may be used at runtime with or without
> installing a virtual address mapping.
> 

With this patch in place Travis CI testing fails:

After 'bootefi selftest' this output is not ejected:
m = u_boot_console.p.expect(['resetting', 'U-Boot'])

And after the reset U-Boot crashes (observed for qemu-arm64_defconfig).

Best regards

Heinrich