module: make it possible to have unsafe, tainting module params

Add flags field to struct kernel_params, and add the first flag: unsafe
parameter. Modifying a kernel parameter with the unsafe flag set, either
via the kernel command line or sysfs, will issue a warning and taint the
kernel.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Jon Mason <jon.mason@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

3 files changed, 47 insertions, 10 deletions

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 1d42dba6121d..bd672948f2f1 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -3587,7 +3587,7 @@ static void __used s8250_options(void)
 #ifdef CONFIG_SERIAL_8250_RSA
         __module_param_call(MODULE_PARAM_PREFIX, probe_rsa,
                 &param_array_ops, .arr = &__param_arr_probe_rsa,
-                0444, -1);
+                0444, -1, 0);
 #endif
 }
 #else
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 16fdddab856a..1e3ffb839daa 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -56,11 +56,21 @@ struct kernel_param_ops {
         void (*free)(void *arg);
 };
 
+/*
+ * Flags available for kernel_param
+ *
+ * UNSAFE - the parameter is dangerous and setting it will taint the kernel
+ */
+enum {
+        KERNEL_PARAM_FL_UNSAFE = (1 << 0)
+};
+
 struct kernel_param {
         const char *name;
         const struct kernel_param_ops *ops;
         u16 perm;
-        s16 level;
+        s8 level;
+        u8 flags;
         union {
                 void *arg;
                 const struct kparam_string *str;
@@ -137,7 +147,7 @@ struct kparam_array
  * The ops can have NULL set or get functions.
  */
 #define module_param_cb(name, ops, arg, perm)                                 \
-        __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1)
+        __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1, 0)
 
 /**
  * <level>_param_cb - general callback for a module/cmdline parameter
@@ -149,7 +159,7 @@ struct kparam_array
  * The ops can have NULL set or get functions.
  */
 #define __level_param_cb(name, ops, arg, perm, level)                   \
-        __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, level)
+        __module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, level, 0)
 
 #define core_param_cb(name, ops, arg, perm)             \
         __level_param_cb(name, ops, arg, perm, 1)
@@ -184,14 +194,14 @@ struct kparam_array
 
 /* This is the fundamental function for registering boot/module
    parameters. */
-#define __module_param_call(prefix, name, ops, arg, perm, level)        \
+#define __module_param_call(prefix, name, ops, arg, perm, level, flags) \
         /* Default value instead of permissions? */                     \
         static const char __param_str_##name[] = prefix #name; \
         static struct kernel_param __moduleparam_const __param_##name   \
         __used                                                          \
     __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
         = { __param_str_##name, ops, VERIFY_OCTAL_PERMISSIONS(perm),    \
-            level, { arg } }
+            level, flags, { arg } }
 
 /* Obsolete - use module_param_cb() */
 #define module_param_call(name, set, get, arg, perm)                    \
@@ -199,7 +209,7 @@ struct kparam_array
                 { 0, (void *)set, (void *)get };                        \
         __module_param_call(MODULE_PARAM_PREFIX,                        \
                             name, &__param_ops_##name, arg,             \
-                            (perm) + sizeof(__check_old_set_param(set))*0, -1)
+                            (perm) + sizeof(__check_old_set_param(set))*0, -1, 0)
 
 /* We don't get oldget: it's often a new-style param_get_uint, etc. */
 static inline int
@@ -279,7 +289,7 @@ static inline void __kernel_param_unlock(void)
  */
 #define core_param(name, var, type, perm)                               \
         param_check_##type(name, &(var));                               \
-        __module_param_call("", name, &param_ops_##type, &var, perm, -1)
+        __module_param_call("", name, &param_ops_##type, &var, perm, -1, 0)
 #endif /* !MODULE */
 
 /**
@@ -297,7 +307,7 @@ static inline void __kernel_param_unlock(void)
                 = { len, string };                                      \
         __module_param_call(MODULE_PARAM_PREFIX, name,                  \
                             &param_ops_string,                          \
-                            .str = &__param_string_##name, perm, -1);   \
+                            .str = &__param_string_##name, perm, -1, 0);\
         __MODULE_PARM_TYPE(name, "string")
 
 /**
@@ -346,6 +356,22 @@ static inline void destroy_params(const struct kernel_param *params,
 #define __param_check(name, p, type) \
         static inline type __always_unused *__check_##name(void) { return(p); }
 
+/**
+ * param_check_unsafe - Warn and taint the kernel if setting dangerous options.
+ *
+ * This gets called from all the standard param setters, but can be used from
+ * custom setters as well.
+ */
+static inline void
+param_check_unsafe(const struct kernel_param *kp)
+{
+        if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
+                pr_warn("Setting dangerous option %s - tainting kernel\n",
+                        kp->name);
+                add_taint(TAINT_USER, LOCKDEP_STILL_OK);
+        }
+}
+
 extern struct kernel_param_ops param_ops_byte;
 extern int param_set_byte(const char *val, const struct kernel_param *kp);
 extern int param_get_byte(char *buffer, const struct kernel_param *kp);
@@ -444,7 +470,7 @@ extern int param_set_bint(const char *val, const struct kernel_param *kp);
         __module_param_call(MODULE_PARAM_PREFIX, name,                  \
                             &param_array_ops,                           \
                             .arr = &__param_arr_##name,                 \
-                            perm, -1);                                  \
+                            perm, -1, 0);                               \
         __MODULE_PARM_TYPE(name, "array of " #type)
 
 extern struct kernel_param_ops param_array_ops;
diff --git a/kernel/params.c b/kernel/params.c
index 8a484fc8bde8..ad8d04563c3a 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -233,6 +233,7 @@ char *parse_args(const char *doing,
 #define STANDARD_PARAM_DEF(name, type, format, strtolfn)                \
         int param_set_##name(const char *val, const struct kernel_param *kp) \
         {                                                               \
+                param_check_unsafe(kp);                                 \
                 return strtolfn(val, 0, (type *)kp->arg);               \
         }                                                               \
         int param_get_##name(char *buffer, const struct kernel_param *kp) \
@@ -265,6 +266,8 @@ int param_set_charp(const char *val, const struct kernel_param *kp)
                 return -ENOSPC;
         }
 
+        param_check_unsafe(kp);
+
         maybe_kfree_parameter(*(char **)kp->arg);
 
         /* This is a hack.  We can't kmalloc in early boot, and we
@@ -302,6 +305,8 @@ EXPORT_SYMBOL(param_ops_charp);
 /* Actually could be a bool or an int, for historical reasons. */
 int param_set_bool(const char *val, const struct kernel_param *kp)
 {
+        param_check_unsafe(kp);
+
         /* No equals means "set"... */
         if (!val) val = "1";
 
@@ -331,6 +336,8 @@ int param_set_invbool(const char *val, const struct kernel_param *kp)
         bool boolval;
         struct kernel_param dummy;
 
+        param_check_unsafe(kp);
+
         dummy.arg = &boolval;
         ret = param_set_bool(val, &dummy);
         if (ret == 0)
@@ -357,6 +364,8 @@ int param_set_bint(const char *val, const struct kernel_param *kp)
         bool v;
         int ret;
 
+        param_check_unsafe(kp);
+
         /* Match bool exactly, by re-using it. */
         boolkp = *kp;
         boolkp.arg = &v;
@@ -476,6 +485,8 @@ int param_set_copystring(const char *val, const struct kernel_param *kp)
 {
         const struct kparam_string *kps = kp->str;
 
+        param_check_unsafe(kp);
+
         if (strlen(val)+1 > kps->maxlen) {
                 pr_err("%s: string doesn't fit in %u chars.\n",
                        kp->name, kps->maxlen-1);