linux-kernel - Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers when requested

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <54106707.4010006@codeaurora.org>
Date:	Wed, 10 Sep 2014 10:58:15 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Doug Anderson <dianders@...omium.org>
CC:	Mark Rutland <mark.rutland@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sonny Rao <sonnyrao@...omium.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clocksource: arch_timer: Fix code to use physical timers
 when requested

On 09/05/2014 06:11 PM, Doug Anderson wrote:
> Mark,
> 
> On Thu, Aug 28, 2014 at 2:35 AM, Mark Rutland <mark.rutland@....com> wrote:
>> Not if you boot Linux at hyp, as we've recommended for this precise
>> reason. That doesn't fix other things like CNTFRQ if the secure
>> initialisation doesn't poke that, however.
> 
> I'll freely admit that I'm out of my league and out of my comfort zone
> here, but...
> 
> In the theory that firmware ought to be as minimal as possible
> (because it's hard to update and hard to keep in sync with kernel
> versions), it seems like firmware ought to start the kernel out in as
> permissive mode as it's willing to provide, right?
> 
> If the kernel is started out as permissive as possible then it can do
> anything it needs to.  Future versions of the kernel can be
> implemented to do any way-cool things that they want to do without an
> update to firmware, right?  ...and current versions of the kernel can
> just shed permissions if they don't want them.
> 
> ...so if I understand correctly, "Secure SVC" mode is more permissive
> than "Non Secure HYP" mode, right?  It looks to me as if we currently
> start the kernel in "Secure SVC" mode.  What do you think about the
> kernel detecting Secure SVC and then dropping down permission levels
> (to Non Secure HYP).  Once it did this, it could update things like
> the virtual offset and then transition down further into non-secure
> SVC mode.
> 
> ...or maybe this has been discussed millions of times already and I'm
> just clueless.  ...or maybe this is just too hard for the kernel to do
> in a generic way?

I think this is a great idea. When running on simulators, it would make (the
non-DTB parts of) the bootwrapper and QEMU's built-in bootloader unnecessary.

Implementing it on AArch64 should be trivial as you can just read CurrentEL
and work from whatever EL/PL you're at. Is there an easy way to check whether
you're in secure or nonsecure mode in AArch32? I seem to recall discussion
about putting this information into the DTB, which makes me think there isn't.

Christopher

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by the Linux Foundation.
--
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/