linux-kernel - Re: [RFC 0/3] extend kexec_file

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Date:	Wed, 13 Jul 2016 16:36:32 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Russell King - ARM Linux <linux@...linux.org.uk>
Cc:	Stewart Smith <stewart@...ux.vnet.ibm.com>,
	Petr Tesarik <ptesarik@...e.cz>,
	linux-arm-kernel@...ts.infradead.org, bhe@...hat.com,
	arnd@...db.de, linuxppc-dev@...ts.ozlabs.org,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>,
	vgoyal@...hat.com
Subject: Re: [RFC 0/3] extend kexec_file_load system call

[snip]
> Now, going back to the more fundamental issue raised in my first reply,
> about the kernel command line.
> 
> On x86, I can see that it _is_ possible for userspace to specify a
> command line, and the kernel loading the image provides the command
> line to the to-be-kexeced kernel with very little checking.  So, if
> your kernel is signed, what stops the "insecure userspace" loading
> a signed kernel but giving it an insecure rootfs and/or console?

The kexec_file_load syscall was introduced for secure boot in the first
place. In case UEFI secure boot the signature verification chain only
covers kernel mode binaries. I think there is such problem in both normal
boot and kexec boot.

Thanks
Dave