From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 06/24] kexec_load: Disable at runtime if the kernel is locked down Date: Wed, 11 Apr 2018 14:00:17 -0500 Message-ID: <87po35k1q6.fsf@xmission.com> References: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> <152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk> (David Howells's message of "Wed, 11 Apr 2018 17:25:18 +0100") Sender: linux-kernel-owner@vger.kernel.org To: David Howells Cc: torvalds@linux-foundation.org, linux-man@vger.kernel.org, linux-api@vger.kernel.org, jmorris@namei.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org List-Id: linux-man@vger.kernel.org David Howells writes: > From: Matthew Garrett > > The kexec_load() syscall permits the loading and execution of arbitrary > code in ring 0, which is something that lock-down is meant to prevent. It > makes sense to disable kexec_load() in this situation. > > This does not affect kexec_file_load() syscall which can check for a > signature on the image to be booted. Maybing I am missing it but I am not seeing anything that would require kexec_file_load be configured such that it checks the loaded kernel. Without that I don't see the point of disabling kexec_load. Nacked-by: "Eric W. Biederman" Eric > Signed-off-by: Matthew Garrett > Signed-off-by: David Howells > Acked-by: Dave Young > Reviewed-by: "Lee, Chun-Yi" > Reviewed-by: James Morris > cc: kexec@lists.infradead.org > --- > > kernel/kexec.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/kexec.c b/kernel/kexec.c > index aed8fb2564b3..1553ac765e73 100644 > --- a/kernel/kexec.c > +++ b/kernel/kexec.c > @@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long nr_segments, > if (!capable(CAP_SYS_BOOT) || kexec_load_disabled) > return -EPERM; > > + /* > + * kexec can be used to circumvent module loading restrictions, so > + * prevent loading in that case > + */ > + if (kernel_is_locked_down("kexec of unsigned images")) > + return -EPERM; > + > /* > * Verify we have a legal set of flags > * This leaves us room for future extensions.