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Subject[PATCH] Make kernel taint on invalid module signatures configurable
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The default kernel behaviour is for unsigned or invalidly signed modules
to load without warning. Right now, If CONFIG_MODULE_SIG is enabled the
kernel will be tainted in this case. Distributions may wish to enable
CONFIG_MODULE_SIG in order to permit signature enforcement, but may not
wish to alter the behaviour of the kernel in the situation where
signature enforcement is not required. Add a new kernel configuration
option to allow the default behaviour to be toggled, and add a kernel
parameter in order to allow tainting to be enabled at runtime.

Signed-off-by: Matthew Garrett <mjg59@google.com>
---

Rusty, with luck this makes it clearer what I'm trying to achieve here.

Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
Documentation/admin-guide/module-signing.rst | 13 +++++++++----
init/Kconfig | 13 ++++++++++++-
kernel/module.c | 7 ++++++-
4 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d9c171ce4190..7ea1e9aeb7d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2291,6 +2291,12 @@
Note that if CONFIG_MODULE_SIG_FORCE is set, that
is always true, so this option does nothing.

+ module.sig_taint
+ [KNL] When CONFIG_MODULE_SIG is set, this means
+ that modules without (valid) signatures will taint the
+ kernel on load. Note that if CONFIG_MODULE_SIG_TAINT is
+ set, that is always true, so this option does nothing.
+
module_blacklist= [KNL] Do not load a comma-separated list of
modules. Useful for debugging problem modules.

diff --git a/Documentation/admin-guide/module-signing.rst b/Documentation/admin-guide/module-signing.rst
index 27e59498b487..96709b93c606 100644
--- a/Documentation/admin-guide/module-signing.rst
+++ b/Documentation/admin-guide/module-signing.rst
@@ -52,10 +52,11 @@ This has a number of options available:
This specifies how the kernel should deal with a module that has a
signature for which the key is not known or a module that is unsigned.

- If this is off (ie. "permissive"), then modules for which the key is not
- available and modules that are unsigned are permitted, but the kernel will
- be marked as being tainted, and the concerned modules will be marked as
- tainted, shown with the character 'E'.
+ If this is off (ie. "permissive"), then modules for which the key
+ is not available and modules that are unsigned are permitted. If
+ ``CONFIG_MODULE_SIG_TAINT`` is enabled or the sig_taint parameter is
+ set the kernel will be marked as being tainted, and the concerned
+ modules will be marked as tainted, shown with the character 'E'.

If this is on (ie. "restrictive"), only modules that have a valid
signature that can be verified by a public key in the kernel's possession
@@ -266,6 +267,10 @@ for which it has a public key. Otherwise, it will also load modules that are
unsigned. Any module for which the kernel has a key, but which proves to have
a signature mismatch will not be permitted to load.

+If ``CONFIG_MODULE_SIG_TAINT`` is enabled or module.sig_taint=1 is
+supplied on the kernel command line, the kernel will be tainted if an
+invalidly signed or unsigned module is loaded.
+
Any module that has an unparseable signature will be rejected.


diff --git a/init/Kconfig b/init/Kconfig
index 8514b25db21c..ffad18a3e890 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.

+config MODULE_SIG_TAINT
+ bool "Taint the kernel on unsigned or incorrectly signed module load"
+ default y
+ depends on MODULE_SIG
+ help
+ Taint the kernel if an unsigned or untrusted 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.
+
config MODULE_SIG_FORCE
bool "Require modules to be validly signed"
depends on MODULE_SIG
help
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_SIG_TAINT is set) taint the kernel.

config MODULE_SIG_ALL
bool "Automatically sign all modules"
diff --git a/kernel/module.c b/kernel/module.c
index 40f983cbea81..70c2edc5693c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -278,6 +278,11 @@ static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
module_param(sig_enforce, bool_enable_only, 0644);
#endif /* !CONFIG_MODULE_SIG_FORCE */

+static bool sig_taint = IS_ENABLED(CONFIG_MODULE_SIG_TAINT);
+#ifndef CONFIG_MODULE_SIG_TAINT
+module_param(sig_taint, bool_enable_only, 0644);
+#endif /* !CONFIG_MODULE_SIG_TAINT */
+
/* Block module loading/unloading? */
int modules_disabled = 0;
core_param(nomodule, modules_disabled, bint, 0);
@@ -3660,7 +3665,7 @@ static int load_module(struct load_info *info, const char __user *uargs,

#ifdef CONFIG_MODULE_SIG
mod->sig_ok = info->sig_ok;
- if (!mod->sig_ok) {
+ if (!mod->sig_ok && sig_taint) {
pr_notice_once("%s: module verification failed: signature "
"and/or required key missing - tainting "
"kernel\n", mod->name);
--
2.14.0.rc1.383.gd1ce394fe2-goog
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