[PATCH V31 18/25] Lock down module params that specify hardware parameters (eg. ioport)

From: Matthew Garrett <matthewgarrett@google.com>
To: jmorris@namei.org
Cc: linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org, dhowells@redhat.com,
	linux-api@vger.kernel.org, luto@kernel.org,
	Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
	Matthew Garrett <mjg59@google.com>
Subject: [PATCH V31 18/25] Lock down module params that specify hardware parameters (eg. ioport)
Date: Tue, 26 Mar 2019 11:27:34 -0700	[thread overview]
Message-ID: <20190326182742.16950-19-matthewgarrett@google.com> (raw)
In-Reply-To: <20190326182742.16950-1-matthewgarrett@google.com>

From: David Howells <dhowells@redhat.com>

Provided an annotation for module parameters that specify hardware
parameters (such as io ports, iomem addresses, irqs, dma channels, fixed
dma buffers and other types).

Suggested-by: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
---
 kernel/params.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/kernel/params.c b/kernel/params.c
index ce89f757e6da..da1297f7cc26 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -108,13 +108,19 @@ bool parameq(const char *a, const char *b)
 	return parameqn(a, b, strlen(a)+1);
 }
 
-static void param_check_unsafe(const struct kernel_param *kp)
+static bool param_check_unsafe(const struct kernel_param *kp,
+			       const char *doing)
 {
 	if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
 		pr_notice("Setting dangerous option %s - tainting kernel\n",
 			  kp->name);
 		add_taint(TAINT_USER, LOCKDEP_STILL_OK);
 	}
+
+	if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
+	    kernel_is_locked_down("Command line-specified device addresses, irqs and dma channels", LOCKDOWN_INTEGRITY))
+		return false;
+	return true;
 }
 
 static int parse_one(char *param,
@@ -144,8 +150,10 @@ static int parse_one(char *param,
 			pr_debug("handling %s with %p\n", param,
 				params[i].ops->set);
 			kernel_param_lock(params[i].mod);
-			param_check_unsafe(&params[i]);
-			err = params[i].ops->set(val, &params[i]);
+			if (param_check_unsafe(&params[i], doing))
+				err = params[i].ops->set(val, &params[i]);
+			else
+				err = -EPERM;
 			kernel_param_unlock(params[i].mod);
 			return err;
 		}
@@ -553,6 +561,12 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
 	return count;
 }
 
+#ifdef CONFIG_MODULES
+#define mod_name(mod) (mod)->name
+#else
+#define mod_name(mod) "unknown"
+#endif
+
 /* sysfs always hands a nul-terminated string in buf.  We rely on that. */
 static ssize_t param_attr_store(struct module_attribute *mattr,
 				struct module_kobject *mk,
@@ -565,8 +579,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
 		return -EPERM;
 
 	kernel_param_lock(mk->mod);
-	param_check_unsafe(attribute->param);
-	err = attribute->param->ops->set(buf, attribute->param);
+	if (param_check_unsafe(attribute->param, mod_name(mk->mod)))
+		err = attribute->param->ops->set(buf, attribute->param);
+	else
+		err = -EPERM;
 	kernel_param_unlock(mk->mod);
 	if (!err)
 		return len;
-- 
2.21.0.392.gf8f6787159e-goog

