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

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Message-ID: <20150316030818.GA14862@dhcp-128-1.nay.redhat.com>
Date:	Mon, 16 Mar 2015 11:08:18 +0800
From:	Minfei Huang <mhuang@...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>, Baoquan He <bhe@...hat.com>,
	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 10:02am, Yinghai Lu wrote:
> On Sun, Mar 15, 2015 at 5:18 AM, Minfei Huang <mhuang@...hat.com> wrote:
> > On 03/15/15 at 12:49am, Yinghai Lu wrote:
> > It confuses me with the virtual address in function parse_kaslr_setup.
> > When we are in here(parse_kaslr_setup), we already use the virtual
> > address, instead of physical address. Is it all right?
> 
> setup_data is using physical address to have linked list.
> 
> we have setup_arch==>parse_setup_data(), that is way before
> init_mem_mapping() to have final kernel mapping setup yet.
> 
> For 64bit, we may use virtual address with help of early mapping with
> #PF handler.
> But 32bit, we don't have that.
> 
> So just use early_memmap to get virtual address to access the value.
> 

Hi, Yinghai!

Thank you for your reply.
I find that the variate kaslr_setup_data is a global variate. Always we
can use physical address to access the value.

But it is more comfortable that we use the early_memmap to access the
value.

Thanks
Minfei

> >
> > In the other words, using physical address in parse_kaslr_setup is
> > always a mistake, whatever the kaslr is on or off.
> >
> 
> The problem is: old code just use physical address as value.
> 
> Thanks
> 
> Yinghai
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