From: James Morris <jmorris@namei.org>
To: Matthew Garrett <matthewgarrett@google.com>
Cc: Jiri Bohac <jbohac@suse.cz>,
linux-api@vger.kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, Matthew Garrett <mjg59@google.com>,
David Howells <dhowells@redhat.com>,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH V34 09/29] kexec_file: Restrict at runtime if the kernel is locked down
Date: Thu, 27 Jun 2019 14:59:09 +1000 (AEST) [thread overview]
Message-ID: <alpine.LRH.2.21.1906271423070.16512@namei.org> (raw)
In-Reply-To: <20190622000358.19895-10-matthewgarrett@google.com>
On Fri, 21 Jun 2019, Matthew Garrett wrote:
> From: Jiri Bohac <jbohac@suse.cz>
>
> When KEXEC_SIG is not enabled, kernel should not load images through
> kexec_file systemcall if the kernel is locked down.
This is not a criticism of the patch but a related issue which I haven't
seen discussed (apologies if it has).
If signed code is loaded into ring 0, verified by the kernel, then
executed, you still lose your secure/trusted/verified boot state. If the
currently running kernel has been runtime-compromised, any signature
verification performed by the kernel cannot be trusted.
This problem is out of scope for the lockdown threat model (which
naturally cannot include a compromised kernel), but folk should be aware
that signature-verified kexec does not provide equivalent assurance to a
full reboot on a secure-boot system.
Potential mitigations here include runtime integrity verification of the
kernel via a separate security monitor (hypervisor, SMM, TEE etc.) or some
kind of platform support for kexec verification.
--
James Morris
<jmorris@namei.org>
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next prev parent reply other threads:[~2019-06-27 4:59 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190622000358.19895-1-matthewgarrett@google.com>
2019-06-22 0:03 ` [PATCH V34 06/29] kexec_load: Disable at runtime if the kernel is locked down Matthew Garrett
2019-06-22 23:52 ` Kees Cook
2019-06-22 0:03 ` [PATCH V34 07/29] Copy secure_boot flag in boot params across kexec reboot Matthew Garrett
2019-06-22 23:53 ` Kees Cook
2019-06-22 0:03 ` [PATCH V34 08/29] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE Matthew Garrett
2019-06-24 2:01 ` Dave Young
2019-06-25 2:35 ` Dave Young
2019-06-22 0:03 ` [PATCH V34 09/29] kexec_file: Restrict at runtime if the kernel is locked down Matthew Garrett
2019-06-22 23:54 ` Kees Cook
2019-06-27 4:59 ` James Morris [this message]
2019-06-27 15:28 ` Matthew Garrett
2019-06-27 18:14 ` James Morris
2019-06-27 23:17 ` Matthew Garrett
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