On Wed, May 29, 2019 at 03:43:50PM -0700, Ke Wu wrote:
> Linux kernel already provide MODULE_SIG and KEXEC_VERIFY_SIG to
> make sure loaded kernel module and kernel image are trusted. This
> patch adds a kernel command line option "loadpin.exclude" which
> allows to exclude specific file types from LoadPin. This is useful
> when people want to use different mechanisms to verify module and
> kernel image while still use LoadPin to protect the integrity of
> other files kernel loads.
Cool; I like this. A few thoughts below...
>
> Signed-off-by: Ke Wu <mik...@google.com>
> ---
> Documentation/admin-guide/LSM/LoadPin.rst | 10 ++++++
> security/loadpin/loadpin.c | 37 +++++++++++++++++++++++
> 2 files changed, 47 insertions(+)
>
> diff --git a/Documentation/admin-guide/LSM/LoadPin.rst
> b/Documentation/admin-guide/LSM/LoadPin.rst
> index 32070762d24c..716ad9b23c9a 100644
> --- 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 055fb0a64169..8ee0c58fea40 100644
> --- a/security/loadpin/loadpin.c
> +++ b/security/loadpin/loadpin.c
> @@ -45,6 +45,8 @@ 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];
Since this is set up at init, let's mark ignore_read_file_id with
__ro_after_init.
> static struct super_block *pinned_root;
> static DEFINE_SPINLOCK(pinned_root_spinlock);
>
> @@ -129,6 +131,12 @@ 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 < READING_MAX_ID && ignore_read_file_id[id]) {
Can you use ARRAY_SIZE(ignore_read_file_id) here instead of
READING_MAX_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) {
> @@ -187,10 +195,37 @@ static struct security_hook_list loadpin_hooks[]
> __lsm_ro_after_init = {
> LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
> };
>
> +static void parse_exclude(void)
Please mark this __init (since it's called from another __init
function).
> +{
> + int i, j;
> + char *cur;
> +
> + 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(kernel_read_file_str); 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;
> }
> @@ -203,3 +238,5 @@ 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");
> --
> 2.22.0.rc1.257.g3120a18244-goog
>
Everything else looks good; thanks!
--
Kees Cook
