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From: Matthew Garrett <matthew.garrett@nebula.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"hpa@zytor.com" <hpa@zytor.com>
Subject: Re: [PATCH V3 02/11] PCI: Lock down BAR access when module security is enabled
Date: Wed, 4 Sep 2013 19:01:54 +0000	[thread overview]
Message-ID: <1378321314.13193.7.camel@x230> (raw)
In-Reply-To: <1378321109.2627.9.camel@shinybook.infradead.org>

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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On Wed, 2013-09-04 at 19:58 +0100, David Woodhouse wrote:
> On Wed, 2013-09-04 at 17:04 +0000, Matthew Garrett wrote:

> > How does virt passthrough work in this case? The current situation
> > appears to be that qemu just passes the BARs through to the guest, and
> > it's the guest that sets things up. We'd need to be able to ensure that
> > there's no way the guest driver can cause DMA into the host kernel.
> 
> We set up the IOMMU page tables so that the virtual bus addresses seen
> by the PCI device are 1:1 mapped to the guest "physical" address space.
> 
> That is, what the PCI device sees as a "physical" address is equivalent
> to what the guest sees as a "physical" address space. It can access
> memory which belongs to that guest, and nothing else. So that should be
> fine.

But presumably the guest's view of RAM is what gets written to the BARs?
I guess if we know it's constrained then there's no need to restrict the
addresses that can be set - we know that they'll be unable to overlap
the host RAM.

-- 
Matthew Garrett <matthew.garrett@nebula.com>
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WARNING: multiple messages have this Message-ID (diff)
From: Matthew Garrett <matthew.garrett-05XSO3Yj/JvQT0dZR+AlfA@public.gmane.org>
To: David Woodhouse <dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org"
	<keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	"hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org"
	<hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH V3 02/11] PCI: Lock down BAR access when module security is enabled
Date: Wed, 4 Sep 2013 19:01:54 +0000	[thread overview]
Message-ID: <1378321314.13193.7.camel@x230> (raw)
In-Reply-To: <1378321109.2627.9.camel-Fexsq3y4057IgHVZqg5X0TlWvGAXklZc@public.gmane.org>

On Wed, 2013-09-04 at 19:58 +0100, David Woodhouse wrote:
> On Wed, 2013-09-04 at 17:04 +0000, Matthew Garrett wrote:

> > How does virt passthrough work in this case? The current situation
> > appears to be that qemu just passes the BARs through to the guest, and
> > it's the guest that sets things up. We'd need to be able to ensure that
> > there's no way the guest driver can cause DMA into the host kernel.
> 
> We set up the IOMMU page tables so that the virtual bus addresses seen
> by the PCI device are 1:1 mapped to the guest "physical" address space.
> 
> That is, what the PCI device sees as a "physical" address is equivalent
> to what the guest sees as a "physical" address space. It can access
> memory which belongs to that guest, and nothing else. So that should be
> fine.

But presumably the guest's view of RAM is what gets written to the BARs?
I guess if we know it's constrained then there's no need to restrict the
addresses that can be set - we know that they'll be unable to overlap
the host RAM.

-- 
Matthew Garrett <matthew.garrett@nebula.com>

  reply	other threads:[~2013-09-04 19:03 UTC|newest]

Thread overview: 108+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-03 23:50 Matthew Garrett
2013-09-03 23:50 ` (unknown), Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 01/11] Add secure_modules() call Matthew Garrett
2013-09-04  0:45   ` James Morris
2013-09-04  0:45     ` James Morris
2013-09-05  2:14   ` joeyli
2013-09-05  2:14     ` joeyli
2013-09-03 23:50 ` [PATCH V3 02/11] PCI: Lock down BAR access when module security is enabled Matthew Garrett
2013-09-04  0:45   ` James Morris
2013-09-04  0:45     ` James Morris
2013-09-04 16:57   ` David Woodhouse
2013-09-04 16:57     ` David Woodhouse
2013-09-04 17:04     ` Matthew Garrett
2013-09-04 17:04       ` Matthew Garrett
2013-09-04 18:58       ` David Woodhouse
2013-09-04 19:01         ` Matthew Garrett [this message]
2013-09-04 19:01           ` Matthew Garrett
2013-09-04 19:31           ` David Woodhouse
2013-09-04 19:31             ` David Woodhouse
2013-09-03 23:50 ` [PATCH V3 03/11] x86: Lock down IO port " Matthew Garrett
2013-09-04  0:45   ` James Morris
2013-09-05  3:52   ` H. Peter Anvin
2013-09-05  3:52     ` H. Peter Anvin
2013-09-05  3:58     ` Matthew Garrett
2013-09-05  3:58       ` Matthew Garrett
2013-09-05 15:36       ` H. Peter Anvin
2013-09-05 15:36         ` H. Peter Anvin
2013-09-03 23:50 ` [PATCH V3 04/11] ACPI: Limit access to custom_method Matthew Garrett
2013-09-04  0:46   ` James Morris
2013-09-04  0:46     ` James Morris
2013-09-03 23:50 ` [PATCH V3 05/11] asus-wmi: Restrict debugfs interface when module loading is restricted Matthew Garrett
2013-09-04  0:46   ` James Morris
2013-09-04  0:46     ` James Morris
2013-09-03 23:50 ` [PATCH V3 06/11] Restrict /dev/mem and /dev/kmem " Matthew Garrett
2013-09-04  0:47   ` James Morris
2013-09-04  0:47     ` James Morris
2013-09-03 23:50 ` [PATCH V3 07/11] acpi: Ignore acpi_rsdp kernel parameter " Matthew Garrett
2013-09-03 23:50   ` Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions Matthew Garrett
2013-09-04  0:48   ` James Morris
2013-09-04  0:48     ` James Morris
2013-09-04 20:09   ` jerry.hoemann
2013-09-04 20:09     ` jerry.hoemann-VXdhtT5mjnY
2013-09-04 20:12     ` Matthew Garrett
2013-09-04 20:12       ` Matthew Garrett
2013-09-04 20:12       ` Matthew Garrett
2013-09-04 20:14     ` Josh Boyer
2013-09-04 20:14       ` Josh Boyer
2013-09-04 20:14       ` Josh Boyer
2013-09-08  6:40   ` Greg KH
2013-09-08  6:40     ` Greg KH
2013-09-08  6:44     ` Matthew Garrett
2013-09-08  6:44       ` Matthew Garrett
2013-09-08  7:24       ` Greg KH
2013-09-08  7:24         ` Greg KH
2013-09-08 14:40         ` Matthew Garrett
2013-09-08 14:40           ` Matthew Garrett
2013-09-08 15:51         ` Kees Cook
2013-09-08 15:51           ` Kees Cook
2013-09-08 16:18           ` Greg KH
2013-09-08 16:18             ` Greg KH
2013-09-08 16:24             ` Matthew Garrett
2013-09-08 16:24               ` Matthew Garrett
2013-09-08 16:39               ` Greg KH
2013-09-08 16:39                 ` Greg KH
2013-09-08 16:59                 ` Matthew Garrett
2013-09-08 16:59                   ` Matthew Garrett
2013-09-08 17:22                   ` Greg KH
2013-09-08 17:22                     ` Greg KH
2013-09-08 17:25                     ` Matthew Garrett
2013-09-08 17:25                       ` Matthew Garrett
2013-09-08 17:11           ` James Bottomley
2013-09-08 17:11             ` James Bottomley
2013-09-08 17:15             ` Matthew Garrett
2013-09-08 17:15               ` Matthew Garrett
2013-09-08 17:22               ` James Bottomley
2013-09-08 17:22                 ` James Bottomley
2013-09-08 17:27                 ` Matthew Garrett
2013-09-08 17:27                   ` Matthew Garrett
2013-09-08 17:32                   ` James Bottomley
2013-09-08 17:32                     ` James Bottomley
2013-09-08 17:38                     ` Matthew Garrett
2013-09-08 17:38                       ` Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 09/11] uswsusp: Disable when module loading is restricted Matthew Garrett
2013-09-04  0:48   ` James Morris
2013-09-04  0:48     ` James Morris
2013-09-05  3:20   ` joeyli
2013-09-05  3:20     ` joeyli
2013-09-03 23:50 ` [PATCH V3 10/11] x86: Restrict MSR access " Matthew Garrett
2013-09-04  0:49   ` James Morris
2013-09-04  0:49     ` James Morris
2013-09-03 23:50 ` [PATCH V3 11/11] Add option to automatically enforce module signatures when in Secure Boot mode Matthew Garrett
2013-09-03 23:50   ` Matthew Garrett
2013-09-04  1:42   ` James Morris
2013-09-04  1:42     ` James Morris
2013-09-04  1:42     ` Matthew Garrett
2013-09-04  1:42       ` Matthew Garrett
2013-09-05  3:13   ` joeyli
2013-09-05  8:24   ` joeyli
2013-09-05  8:24     ` joeyli
2013-09-05 10:16   ` Matt Fleming
2013-09-05 10:16     ` Matt Fleming
2013-09-05 12:54     ` Matthew Garrett
2013-09-05 12:54       ` Matthew Garrett
2013-09-04 15:53 ` Kees Cook
2013-09-04 15:53   ` Re: Kees Cook
2013-09-04 16:05   ` Re: Josh Boyer
2013-09-04 16:05     ` Re: Josh Boyer

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