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

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Message-ID: <20150316051152.GE26587@dhcp-16-105.nay.redhat.com>
Date:	Mon, 16 Mar 2015 13:11:52 +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 09:36pm, 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.
> >
> > 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. And also parse_kaslr_setup is a function specified to
> > handle kaslr, it doesn't make me uncomfortable to implement with a
> > specific knowledge which here means the setup_data is a global varialbe
> > in kernel code and no need to do early_memremap since mapping has been
> > built .
> 
> I should not put that checking in. even parse_setup_data does not check
> early_memmap return.

Yes, I think so. Otherwise it involves incorrect handling. 

Still I think no need to do early_memremap. Because kaslr_setup_data is
ident mapped, it's not like other setup_data info which is passed in
from bootloader. But I am fine too if only do early_memremap
without checking.


Thanks
Baoquan

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