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

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Date:	Thu, 06 Jun 2013 12:28:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Matt Fleming <matt@...sole-pimps.org>,
	Linux EFI <linux-efi@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Jiri Kosina <jkosina@...e.cz>, X86-ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 4/4] x86, efi: Map runtime services 1:1

On 06/06/2013 08:58 AM, Borislav Petkov wrote:
> --
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 654be4ae3047..7a6129afdff1 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1021,6 +1021,9 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code)
>  	/* Get the faulting address: */
>  	address = read_cr2();
>  
> +	if (read_cr3() == (unsigned long)real_mode_header->trampoline_pgd)
> +		pr_err("%s: #PF addr: 0x%lx\n", __func__, address);
> +
>  	/*
>  	 * Detect and handle instructions that would cause a page fault for
>  	 * both a tracked kernel page and a userspace page.
> 

Or we could materialize mappings for this specific PGD.  However, adding
a read of %cr3 in __do_page_fault sounds expensive.

	-hpa

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