linux-kernel - Re: [Techteam] [RFC PATCH] x86-32: Start out eflags and cr4 clean

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <50FA4EC7.6060402@laptop.org>
Date:	Fri, 18 Jan 2013 21:44:07 -1000
From:	Mitch Bradley <wmb@...top.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
CC:	Andres Salomon <dilinger@...ued.net>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, techteam@...ts.laptop.org,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [Techteam] [RFC PATCH] x86-32: Start out eflags and cr4 clean



On 1/18/2013 4:35 PM, H. Peter Anvin wrote:
> On 01/18/2013 05:05 PM, Mitch Bradley wrote:
>>
>>
>> On 1/18/2013 2:42 PM, H. Peter Anvin wrote:
>>> On 01/18/2013 04:40 PM, Andres Salomon wrote:
>>>> Bad news on this patch; I've been told that it breaks booting on an
>>>> XO-1.5.  Does anyone from OLPC know why yet?
>>>
>>> What are the settings of CR0 and CR4 on kernel entry on XO-1.5?
>>
>>
>> CR0 is 0x80000011
>> CR4 is 0x10
>>
> 
> OK, that makes sense... the kernel doesn't enable the PSE bit yet and I
> bet that's what you're using for the non-stolen page tables.

Indeed, we are using 4M pages to map the firmware into high virtual
addresses.

> 
> Can we simply disable paging before mucking with CR4?  The other option
> that I can see is to always enable PSE and PGE, since they are simply
> features opt-ins that don't do any harm if unused.  At the same time,
> though, entering the kernel through the default_entry path with paging
> enabled is definitely not anything the kernel expects.
> 
> Does this patch work for you?  Since we have ditched 386 support, we can
> mimic x86-64 (yay, one more difference gone!) and just use a predefined
> value for %cr0 (the FPU flags need to change if we are on an FPU-less
> chip, but that happens during FPU probing.)
> 
> Does this patch work for you?

We will test it and get back to you.

> 
> 	-hpa
> 
> 
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/