| Message ID | 152346391877.4030.6270466586590461223.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
David Howells <dhowells@redhat.com> writes: > From: Matthew Garrett <mjg59@srcf.ucam.org> > > 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" <ebiederm@xmission.com> Eric > Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org> > Signed-off-by: David Howells <dhowells@redhat.com> > Acked-by: Dave Young <dyoung@redhat.com> > Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com> > Reviewed-by: James Morris <james.l.morris@oracle.com> > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Eric W. Biederman <ebiederm@xmission.com> wrote: > 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. I meant to remove this patch too. David -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote: > David Howells <dhowells@redhat.com> writes: > > > From: Matthew Garrett <mjg59@srcf.ucam.org> > > > > 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" <ebiederm@xmission.com> The IMA "secure boot" policy requires the kexec image to be signed. This call to kernel_is_locked_down() could be replaced with a call to security_kernel_read_file(NULL, READING_KEXEC_IMAGE). It would be similar to the existing init_module syscall calling security_kernel_read_file(). Mimi -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 2018-04-11 at 16:09 -0400, Mimi Zohar wrote: > On Wed, 2018-04-11 at 14:00 -0500, Eric W. Biederman wrote: > > David Howells <dhowells@redhat.com> writes: > > > > > From: Matthew Garrett <mjg59@srcf.ucam.org> > > > > > > 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" <ebiederm@xmission.com> > > The IMA "secure boot" policy requires the kexec image to be signed. > This call to kernel_is_locked_down() could be replaced with a call > to security_kernel_read_file(NULL, READING_KEXEC_IMAGE). > > It would be similar to the existing init_module syscall calling > security_kernel_read_file(). David, enabling the IMA-appraisal "secure boot" policy should probably not be dependent on lockdown either. Mimi -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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.