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Date: Wed, 11 May 2016 08:23:45 -0700
From: Kees Cook <keescook@...omium.org>
To: Ingo Molnar <mingo@...nel.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 <lasse.collin@...aani.org>, Andrew Morton <akpm@...ux-foundation.org>,
Dave Young <dyoung@...hat.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 1/4] x86/KASLR: Clarify identity map interface
On Tue, May 10, 2016 at 11:24 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * 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.
It's the issue described at the top of misc.c:
/*
* WARNING!!
* This code is compiled with -fPIC and it is relocated dynamically at
* run time, but no relocation processing is performed. This means that
* it is not safe to place pointers in static structures.
*/
Should this be repeated in each .c file maybe as a reminder?
If the rest of the patches look good, we could clean this up as a
following patch? What do you think?
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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