linux-kernel - Re: [PATCH v8 1/4] x86/KASLR: Clarify identity map interface

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Message-ID: <20160511062442.GA24803@gmail.com>
Date:	Wed, 11 May 2016 08:24:42 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Borislav Petkov <bp@...e.de>, Yinghai Lu <yinghai@...nel.org>,
	Baoquan He <bhe@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>,
	kernel-hardening@...ts.openwall.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 1/4] x86/KASLR: Clarify identity map interface


* Kees Cook <keescook@...omium.org> wrote:

> +/*
> + * Mapping information structure passed to kernel_ident_mapping_init().
> + * Due to relocation, pointers must be assigned at run time not build time.
> + */
> +static struct x86_mapping_info mapping_info = {
> +	.pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
> +};

> +void initialize_identity_maps(void)
>  {
> +	/* Init mapping_info with run-time function/buffer pointers. */
> +	mapping_info.alloc_pgt_page = alloc_pgt_page;
> +	mapping_info.context = &pgt_data;

Could you please outline the precise failure mode? What gets executed when, which 
pointer gets relocated and which not, and exactly when does it pose a problem, 
etc.

Thanks,

	Ingo