Re: [PATCH -v2 4/4] x86, efi: Map runtime services 1:1

Matt Fleming
2013-06-21T11:56:32Z

On Mon, 17 Jun, at 07:50:16PM, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
>
> Due to the braindead design of EFI, we cannot map runtime services more
> than once for the duration of a booted system. Thus, if we want to use
> EFI runtime services in a kexec'ed kernel, maybe the only possible and
> sensible approach would be to map them 1:1 so that when the kexec kernel
> loads, it can simply call those addresses without the need for remapping
> (which doesn't work anyway).
>
> Furthermore, this mapping approach could be of help with b0rked EFI
> implementations for a different set of reasons.
>
> This implementation is 64-bit only for now.
>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> ---
> arch/x86/include/asm/efi.h | 67 +++++++++++----
> arch/x86/platform/efi/efi.c | 165 +++++++++++++++++++++++++++++-------
> arch/x86/platform/efi/efi_stub_64.S | 56 ++++++++++++
> 3 files changed, 240 insertions(+), 48 deletions(-)

[...]

> + .macro SWITCH_PGT
> + cmpb $0, efi_use_11_map
> + je 1f;

Actually, this needs to be,

cmpb $0, efi_use_11_map(%rip)

because this code is built into the EFI boot stub which isn't loaded at
a fixed address and needs to be position independent.

--
Matt Fleming, Intel Open Source Technology Center