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

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Date:	Fri, 21 Jun 2013 12:56:28 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linux EFI <linux-efi@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH -v2 4/4] x86, efi: Map runtime services 1:1

On Mon, 17 Jun, at 07:50:16PM, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.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@...e.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
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