[U-Boot] [PATCH v4 19/21] sandbox: Allow to execute from RAM

[Simon Glass]

Hi Alex,

On 21 June 2018 at 03:44, Alexander Graf <agraf at suse.de> wrote:
> On 06/21/2018 04:02 AM, Simon Glass wrote:
>>
>> Hi Alex,
>>
>> On 18 June 2018 at 09:23, Alexander Graf <agraf at suse.de> wrote:
>>>
>>> With efi_loader, we may want to execute payloads from RAM. By default,
>>> permissions on the RAM region don't allow us to execute from there
>>> though.
>>>
>>> So whenever we get into the efi_loader case, let's mark RAM as
>>> executable.
>>> That way we still protect normal cases, but allow for efi binaries to
>>> directly get executed from within RAM.
>>>
>>> For this, we hook into the already existing allow_unaligned() call which
>>> also transitions the system over into semantics required by the UEFI
>>> specification.
>>>
>>> Signed-off-by: Alexander Graf <agraf at suse.de>
>>> ---
>>>   arch/sandbox/cpu/cpu.c | 14 ++++++++++++++
>>>   arch/sandbox/cpu/os.c  | 14 ++++++++++++++
>>>   include/os.h           | 19 +++++++++++++++++++
>>>   3 files changed, 47 insertions(+)
>>>
>> What is this patch actually for? Does it make something work that did
>> not before? Where is it called?
>
>
> At least on aarch64 executing from the RAM region fails on the first
> instruction you call inside it, because it's not mapped with PROT_EXEC. I
> think not mapping it with PROT_EXEC is a good thing in the normal sandbox
> use case, but for EFI we need to run from RAM ;).
>
> So yes, this patch makes that work. It's called from allow_unaligned() which
> gets called from the bootefi command function.

OK I see. This is so that sandbox running on an ARM platform can
actually load and run an EFI application, right?

Can you please make this code and commit message ARM-specific? Also,
just call your code on start-up in cpu.c. We don't need to connect to
an allow_unaligned() thing, which is a misnomer in this case.

Regards,
Simon