[PATCH] Allow automatic kernel taint on unsigned module load to be disabled

From: Matthew Garrett
Date: Fri Aug 04 2017 - 14:08:19 EST

Distributions may wish to provide kernels that permit loading of
unsigned modules based on certain policy decisions. Right now that
results in the kernel being tainted whenever an unsigned module is
loaded, which may not be desirable. Add a config option to disable that.

Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
init/Kconfig | 13 ++++++++++++-
kernel/module.c | 2 ++
2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 8514b25db21c..196860c5d1e5 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1749,12 +1749,23 @@ config MODULE_SIG
debuginfo strip done by some packagers (such as rpmbuild) and
inclusion into an initramfs that wants the module size reduced.

+ bool "Taint the kernel if unsigned modules are loaded"
+ default y
+ depends on MODULE_SIG
+ help
+ Taint the kernel if an unsigned kernel module is loaded. If this
+ option is enabled, the kernel will be tainted on an attempt to load
+ an unsigned module or signed modules for which we don't have a key
+ even if signature enforcement is disabled.
bool "Require modules to be validly signed"
depends on MODULE_SIG
Reject unsigned modules or signed modules for which we don't have a
- key. Without this, such modules will simply taint the kernel.
+ key. Without this, such modules will be loaded successfully but will
+ (if MODULE_UNSIGNED_TAINT is set) taint the kernel.

bool "Automatically sign all modules"
diff --git a/kernel/module.c b/kernel/module.c
index 40f983cbea81..71f80c8816f2 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3660,12 +3660,14 @@ static int load_module(struct load_info *info, const char __user *uargs,

mod->sig_ok = info->sig_ok;
if (!mod->sig_ok) {
pr_notice_once("%s: module verification failed: signature "
"and/or required key missing - tainting "
"kernel\n", mod->name);

/* To avoid stressing percpu allocator, do this once we're unique. */