Merge tag 'loadpin-v5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees...

Pull security/loadpin updates from Kees Cook:

 - Allow exclusion of specific file types (Ke Wu)

* tag 'loadpin-v5.3-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  security/loadpin: Allow to exclude specific file types

diff --git a/Documentation/admin-guide/LSM/LoadPin.rst b/Documentation/admin-guide/LSM/LoadPin.rst
index 32070762d24c44f0efc47a7bb1e99e2cf9d18291..716ad9b23c9aa73115c21ee86538cf99cd7ec173 100644 (file)
--- a/Documentation/admin-guide/LSM/LoadPin.rst
+++ b/Documentation/admin-guide/LSM/LoadPin.rst
@@ -19,3 +19,13 @@ block device backing the filesystem is not read-only, a sysctl is
 created to toggle pinning: ``/proc/sys/kernel/loadpin/enabled``. (Having
 a mutable filesystem means pinning is mutable too, but having the
 sysctl allows for easy testing on systems with a mutable filesystem.)
+
+It's also possible to exclude specific file types from LoadPin using kernel
+command line option "``loadpin.exclude``". By default, all files are
+included, but they can be excluded using kernel command line option such
+as "``loadpin.exclude=kernel-module,kexec-image``". This allows to use
+different mechanisms such as ``CONFIG_MODULE_SIG`` and
+``CONFIG_KEXEC_VERIFY_SIG`` to verify kernel module and kernel image while
+still use LoadPin to protect the integrity of other files kernel loads. The
+full list of valid file types can be found in ``kernel_read_file_str``
+defined in ``include/linux/fs.h``.

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 79131efa963431736f3b11435a1cff7865ff3978..81519c804888c613fb86afc164f67238fcd333ba 100644 (file)
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -37,6 +37,8 @@ static void report_load(const char *origin, struct file *file, char *operation)
 }
 
 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
+static char *exclude_read_files[READING_MAX_ID];
+static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
 static struct super_block *pinned_root;
 static DEFINE_SPINLOCK(pinned_root_spinlock);
 
@@ -121,6 +123,13 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
        struct super_block *load_root;
        const char *origin = kernel_read_file_id_str(id);
 
+       /* If the file id is excluded, ignore the pinning. */
+       if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
+           ignore_read_file_id[id]) {
+               report_load(origin, file, "pinning-excluded");
+               return 0;
+       }
+
        /* This handles the older init_module API that has a NULL file. */
        if (!file) {
                if (!enforce) {
@@ -179,10 +188,47 @@ static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
        LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
 };
 
+static void __init parse_exclude(void)
+{
+       int i, j;
+       char *cur;
+
+       /*
+        * Make sure all the arrays stay within expected sizes. This
+        * is slightly weird because kernel_read_file_str[] includes
+        * READING_MAX_ID, which isn't actually meaningful here.
+        */
+       BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
+                    ARRAY_SIZE(ignore_read_file_id));
+       BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
+                    ARRAY_SIZE(ignore_read_file_id));
+
+       for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
+               cur = exclude_read_files[i];
+               if (!cur)
+                       break;
+               if (*cur == '\0')
+                       continue;
+
+               for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
+                       if (strcmp(cur, kernel_read_file_str[j]) == 0) {
+                               pr_info("excluding: %s\n",
+                                       kernel_read_file_str[j]);
+                               ignore_read_file_id[j] = 1;
+                               /*
+                                * Can not break, because one read_file_str
+                                * may map to more than on read_file_id.
+                                */
+                       }
+               }
+       }
+}
+
 static int __init loadpin_init(void)
 {
        pr_info("ready to pin (currently %senforcing)\n",
                enforce ? "" : "not ");
+       parse_exclude();
        security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
        return 0;
 }
@@ -195,3 +241,5 @@ DEFINE_LSM(loadpin) = {
 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
 module_param(enforce, int, 0);
 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
+module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
+MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");