From: Stewart Smith <stewart@linux.vnet.ibm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Baoquan He <bhe@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
"kexec\@lists.infradead.org" <kexec@lists.infradead.org>,
Dave Young <dyoung@redhat.com>, Petr Tesarik <ptesarik@suse.cz>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Vivek Goyal <vgoyal@redhat.com>,
AKASHI Takahiro <takahiro.akashi@linaro.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
"linux-arm-kernel\@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 0/3] extend kexec_file_load system call
Date: Wed, 13 Jul 2016 18:20:10 +1000 [thread overview]
Message-ID: <87mvlmne4l.fsf@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAKv+Gu9kEeVuW6Hj7HYOMojE5SLEZ69uAW2t9xZySw0uWNLcBQ@mail.gmail.com>
Ard Biesheuvel <ard.biesheuvel@linaro.org> writes:
> On 13 July 2016 at 09:36, Russell King - ARM Linux
> <linux@armlinux.org.uk> wrote:
>> On Wed, Jul 13, 2016 at 02:59:51PM +1000, Stewart Smith wrote:
>>> Russell King - ARM Linux <linux@armlinux.org.uk> writes:
>>> > On Tue, Jul 12, 2016 at 10:58:05PM +0200, Petr Tesarik wrote:
>>> >> I'm not an expert on DTB, so I can't provide an example of code
>>> >> execution, but you have already mentioned the /chosen/linux,stdout-path
>>> >> property. If an attacker redirects the bootloader to an insecure
>>> >> console, they may get access to the system that would otherwise be
>>> >> impossible.
>>> >
>>> > I fail to see how kexec connects with the boot loader - the DTB image
>>> > that's being talked about is one which is passed from the currently
>>> > running kernel to the to-be-kexec'd kernel. For ARM (and I suspect
>>> > also ARM64) that's a direct call chain which doesn't involve any
>>> > boot loader or firmware, and certainly none that would involve the
>>> > passed DTB image.
>>>
>>> For OpenPOWER machines, kexec is the bootloader. Our bootloader is a
>>> linux kernel and initramfs with a UI (petitboot) - this means we never
>>> have to write a device driver twice: write a kernel one and you're done
>>> (for booting from the device and using it in your OS).
>>
>> I think you misunderstood my point.
>>
>> On ARM, we do not go:
>>
>> kernel (kexec'd from) -> boot loader -> kernel (kexec'd to)
>>
>> but we go:
>>
>> kernel (kexec'd from) -> kernel (kexec'd to)
>>
>> There's no intermediate step involving any bootloader.
>>
>> Hence, my point is that the dtb loaded by kexec is _only_ used by the
>> kernel which is being kexec'd to, not by the bootloader, nor indeed
>> the kernel which it is loaded into.
>>
>> Moreover, if you read the bit that I quoted (which is what I was
>> replying to), you'll notice that it is talking about the DTB loaded
>> by kexec somehow causing the _bootloader_ to be redirected to an
>> alternative console. This point is wholely false on ARM.
>>
>
> The particular example may not apply, but the argument that the DTB
> -as a description of the hardware topology- needs to be signed if the
> kernel is also signed is valid. We do the same in the UEFI stub, i.e.,
> it normally takes a dtb= argument to allow the DTB to be overridden,
> but this feature is disabled when Secure Boot is in effect. By the
> same reasoning, if any kind of kexec kernel image validation is in
> effect, we should either validate the DTB image as well, or disallow
> external DTBs and only perform kexec with the kernel's current DTB
> (the blob it was booted with, not the unflattened data structure)
DTB booted with != current description of hardware
We could have had: PCI hotplug, CPU/memory/cache offlined due to
hardware error, change in available pstates / CPU frequencies.
There is merit in having a signed dtb if you're booting a signed kernel
in a secure boot scenario. However, we still need to set up /chosen/ and
we still need a way to do something like the offb hack.
--
Stewart Smith
OPAL Architect, IBM.
next prev parent reply other threads:[~2016-07-13 8:20 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-12 1:41 [RFC 0/3] extend kexec_file_load system call AKASHI Takahiro
2016-07-12 1:41 ` [RFC 1/3] syscall: add kexec_file_load to generic unistd.h AKASHI Takahiro
2016-07-12 1:42 ` [RFC 2/3] kexec: add dtb info to struct kimage AKASHI Takahiro
2016-07-12 1:42 ` [RFC 3/3] kexec: extend kexec_file_load system call AKASHI Takahiro
2016-07-15 13:09 ` Vivek Goyal
2016-07-15 13:19 ` Mark Rutland
2016-07-18 2:30 ` Dave Young
2016-07-18 10:07 ` Mark Rutland
2016-07-19 0:55 ` Dave Young
2016-07-19 10:52 ` Mark Rutland
2016-07-19 12:24 ` Vivek Goyal
2016-07-19 12:47 ` Mark Rutland
2016-07-19 13:26 ` Vivek Goyal
2016-07-20 11:41 ` David Laight
2016-07-21 9:21 ` Russell King - ARM Linux
2016-07-18 2:33 ` Dave Young
2016-07-27 0:24 ` [PATCH v2 " Thiago Jung Bauermann
2016-08-05 20:46 ` Thiago Jung Bauermann
2016-07-12 13:25 ` [RFC 0/3] " Eric W. Biederman
2016-07-12 13:58 ` Thiago Jung Bauermann
2016-07-12 14:02 ` Vivek Goyal
2016-07-12 23:45 ` Stewart Smith
2016-07-13 13:27 ` Vivek Goyal
2016-07-12 14:02 ` Arnd Bergmann
2016-07-12 14:18 ` Vivek Goyal
2016-07-12 14:24 ` Arnd Bergmann
2016-07-12 14:50 ` Mark Rutland
2016-07-13 2:36 ` Dave Young
2016-07-13 8:01 ` Arnd Bergmann
2016-07-13 8:23 ` Stewart Smith
2016-07-13 9:41 ` Mark Rutland
2016-07-13 13:13 ` Arnd Bergmann
2016-07-13 18:45 ` Thiago Jung Bauermann
2016-07-13 19:59 ` Arnd Bergmann
2016-07-14 2:18 ` Thiago Jung Bauermann
2016-07-14 8:29 ` Arnd Bergmann
2016-07-15 1:44 ` Thiago Jung Bauermann
2016-07-15 7:31 ` Arnd Bergmann
2016-07-15 13:26 ` Vivek Goyal
2016-07-15 13:33 ` Mark Rutland
2016-07-15 15:29 ` Thiago Jung Bauermann
2016-07-15 15:47 ` Mark Rutland
2016-07-15 13:42 ` Russell King - ARM Linux
2016-07-15 20:26 ` Arnd Bergmann
2016-07-15 21:03 ` Thiago Jung Bauermann
2016-07-22 0:09 ` Thiago Jung Bauermann
2016-07-22 0:53 ` Jeremy Kerr
2016-07-22 2:54 ` Michael Ellerman
2016-07-22 20:41 ` Thiago Jung Bauermann
2016-07-15 8:49 ` Russell King - ARM Linux
2016-07-15 13:03 ` Vivek Goyal
2016-07-13 9:34 ` Mark Rutland
2016-07-13 17:38 ` AKASHI Takahiro
2016-07-13 17:58 ` Mark Rutland
2016-07-13 19:57 ` Arnd Bergmann
2016-07-14 12:42 ` Mark Rutland
2016-07-14 1:54 ` Dave Young
2016-07-14 1:50 ` Dave Young
2016-07-12 16:25 ` Thiago Jung Bauermann
2016-07-12 20:58 ` Petr Tesarik
2016-07-12 21:22 ` Eric W. Biederman
2016-07-12 21:36 ` Eric W. Biederman
2016-07-12 21:53 ` Petr Tesarik
2016-07-12 22:18 ` Russell King - ARM Linux
2016-07-13 4:59 ` Stewart Smith
2016-07-13 7:36 ` Russell King - ARM Linux
2016-07-13 7:47 ` Ard Biesheuvel
2016-07-13 8:09 ` Russell King - ARM Linux
2016-07-13 8:20 ` Stewart Smith [this message]
2016-07-13 7:55 ` Stewart Smith
2016-07-13 8:26 ` Russell King - ARM Linux
2016-07-13 8:36 ` Dave Young
2016-07-13 8:57 ` Petr Tesarik
2016-07-13 13:03 ` Vivek Goyal
2016-07-13 17:40 ` Russell King - ARM Linux
2016-07-13 18:22 ` Vivek Goyal
2016-07-18 12:46 ` Balbir Singh
2016-07-18 13:26 ` Vivek Goyal
2016-07-18 13:38 ` Vivek Goyal
2016-07-20 3:45 ` Balbir Singh
2016-07-20 8:35 ` Russell King - ARM Linux
2016-07-20 11:12 ` Arnd Bergmann
2016-07-20 15:50 ` Thiago Jung Bauermann
2016-07-20 12:46 ` Vivek Goyal
2016-07-20 12:27 ` Vivek Goyal
2016-07-12 23:41 ` Stewart Smith
2016-07-13 13:25 ` Vivek Goyal
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