loader: Allocate trampoline as EfiLoaderCode, not Data

[jim.chen.1827_gmail.com]

I tested this patch on the nigeria-sp7 in the Kitchener office, and it resolves an exception that originally took place during the loader stage.

[kib]

stand/efi/loader/arch/amd64/elf64_freebsd.c

114

The trampoline stack is located at the same page as code. So for EfiLoaderCode, could it be that some fw would deny the write?

[emaste]

stand/efi/loader/arch/amd64/elf64_freebsd.c

114

I am not certain, but believe that we will get only RWX or RW from AllocatePages for code or data. It may happen for PE image sections but not for allocations, I think.

If this is a concern we'd need to split into two allocations I suppose. Or EFI_MEMORY_ATTRIBUTE_PROTOCOL

[imp]

This should be fine.

[imp]

So you can't allocate pages for code read only... you've got to write to them sometime and there's no interface to change the mapping.

[emaste]

EFI_MEMORY_ATTRIBUTE_PROTOCOL is the interface to change mapping

[imp]

In D58383#1339358, @emaste wrote:

EFI_MEMORY_ATTRIBUTE_PROTOCOL is the interface to change mapping

Oh! That's shiny. I'll have to try that out... While sharing the stack and trampoline code is super-old-school, I know that some uses of that cause security problems... So far none here, but we'll keep this in mind if something pops up or I get a bunch of time to test it, etc, which I might have later in the year.