[PATCH V40 06/29] kexec_load: Disable at runtime if the kernel is locked down
From: Matthew Garrett <hidden>
Date: 2019-08-20 00:18:30
Also in:
kexec, linux-api, lkml
Subsystem:
kexec, lockdown security module, security subsystem, the rest · Maintainers:
Andrew Morton, Baoquan He, Mike Rapoport, Pasha Tatashin, Pratyush Yadav, Nicolas Bouchinet, Xiu Jianfeng, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
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. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Matthew Garrett <redacted> Acked-by: Dave Young <redacted> Reviewed-by: Kees Cook <redacted> cc: kexec@lists.infradead.org Signed-off-by: James Morris <jmorris@namei.org> --- include/linux/security.h | 1 + kernel/kexec.c | 8 ++++++++ security/lockdown/lockdown.c | 1 + 3 files changed, 10 insertions(+)
diff --git a/include/linux/security.h b/include/linux/security.h
index e5dd446ef35b..b607a8ac97fe 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h@@ -105,6 +105,7 @@ enum lockdown_reason { LOCKDOWN_NONE, LOCKDOWN_MODULE_SIGNATURE, LOCKDOWN_DEV_MEM, + LOCKDOWN_KEXEC, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_CONFIDENTIALITY_MAX, };
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 1b018f1a6e0d..bc933c0db9bf 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c@@ -205,6 +205,14 @@ static inline int kexec_load_check(unsigned long nr_segments, if (result < 0) return result; + /* + * kexec can be used to circumvent module loading restrictions, so + * prevent loading in that case + */ + result = security_locked_down(LOCKDOWN_KEXEC); + if (result) + return result; + /* * Verify we have a legal set of flags * This leaves us room for future extensions.
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 240ecaa10a1d..aaf30ad351f9 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c@@ -20,6 +20,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_NONE] = "none", [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading", [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port", + [LOCKDOWN_KEXEC] = "kexec of unsigned images", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };
--
2.23.0.rc1.153.gdeed80330f-goog