linux-kernel - Re: [PATCH v4] x86, kaslr: Access the correct kaslr

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Date:	Mon, 16 Mar 2015 13:19:35 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jiri Kosina <jkosina@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v4] x86, kaslr: Access the correct kaslr_enabled variable

On 03/15/15 at 10:04pm, Yinghai Lu wrote:
> On Sun, Mar 15, 2015 at 8:28 PM, Baoquan He <bhe@...hat.com> wrote:
> > On 03/15/15 at 12:49am, Yinghai Lu wrote:
> >
> > It's good to check the ret value as Boris suggested. However it could
> > fail since early_memremap self fail, e.g slot not found. In this case
> > making kaslr_enabled true may not be good.
> 
> It should not fail. we always follow map/access/unmap. and sometime
> would have two for copying between them.

Well, then I would say if add checking too in other places for
setup_data handling, e.g parse_setup_data you mentioned. Or don't check
at all place to make them consistent. 

> 
> >
> > As Minfei talked with you kaslr_setup_data is a global variable inside
> > kernel code, it has been ident mapped. Just derefencing the physical
> > address which is virtual address too and getting the real stored value
> > may be safer.
> 
> No.
> That ident mapping is set in arch/x86/kernel/head_64.S and it
> is only for switchover. and it is gone when
> arch/x86/kernel/head64.c::x86_64_start_kernel/reset_early_page_tables
> is called.
> 
> That reset_early_page_tables will only keep kernel high mapping
> and clear all other.

Ah, yes. You are right. I didn't get this clearly, Thanks for telling.

Thanks
Baoquan

> 
> Thanks
> 
> Yinghai
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