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Message-ID: <alpine.LRH.2.21.1905311058560.16993@namei.org>
Date: Fri, 31 May 2019 10:59:16 +1000 (AEST)
From: James Morris <jmorris@...ei.org>
To: Kees Cook <keescook@...omium.org>
cc: Ke Wu <mikewu@...gle.com>, Jonathan Corbet <corbet@....net>,
"Serge E. Hallyn" <serge@...lyn.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH v2] Allow to exclude specific file types in LoadPin
On Thu, 30 May 2019, Kees Cook wrote:
> On Thu, May 30, 2019 at 12:22:08PM -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.
> >
> > Signed-off-by: Ke Wu <mikewu@...gle.com>
>
> Thanks for the updates!
>
> Acked-by: Kees Cook <keescook@...omium.org>
>
> James, I don't have anything else planned for loadpin this cycle. Do you
> want me to push this to Linus in the next cycle, or do you want to take
> it into one of your trees?
You should push it directly to Linus.
>
> Thanks!
>
> -Kees
>
> > ---
> > Changelog since v1:
> > - Mark ignore_read_file_id with __ro_after_init.
> > - Mark parse_exclude() with __init.
> > - Use ARRAY_SIZE(ignore_read_file_id) instead of READING_MAX_ID.
> >
> >
> > Documentation/admin-guide/LSM/LoadPin.rst | 10 ++++++
> > security/loadpin/loadpin.c | 38 +++++++++++++++++++++++
> > 2 files changed, 48 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..d5f064644c54 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] __ro_after_init;
> > static struct super_block *pinned_root;
> > static DEFINE_SPINLOCK(pinned_root_spinlock);
> >
> > @@ -129,6 +131,13 @@ 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) {
> > @@ -187,10 +196,37 @@ 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;
> > +
> > + 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 +239,5 @@ 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
> >
>
>
--
James Morris
<jmorris@...ei.org>
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