This patch series allows to disable module validity enforcement
in runtime through /sys/kernel/security/modsign/enforce interface.
Assuming CONFIG_MODULE_SIG_FORCE=y, here are the instructions to
disable the validity enforcement.
# cat /sys/kernel/security/modsign/enforce
# echo -n 0 > data
# openssl smime -sign -nocerts -noattr -binary -in data \
-inkey <system_trusted_key> -signer <cert> -outform der \
-out /sys/kernel/security/modsign/enforce
Now enable enforcement again on demand.
# echo 1 > /sys/kernel/security/modsign/enforce
Changelog:
v2:
- Support to disable validity enforcement in runtime.
/sys/kernel/security/modsign/enforce gives the result of current
enforcement policy of loading module.
Signed-off-by: Jia Zhang <[email protected]>
---
kernel/module.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/kernel/module.c b/kernel/module.c
index 79825ea..6b032577 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2794,11 +2794,60 @@ static int module_sig_check(struct load_info *info, int flags)
return err;
}
+
+#ifdef CONFIG_SECURITYFS
+static ssize_t modsign_enforce_read(struct file *filp, char __user *ubuf,
+ size_t count, loff_t *offp)
+{
+ char buf[2];
+
+ sprintf(buf, "%d", is_module_sig_enforced());
+
+ return simple_read_from_buffer(ubuf, count, offp, buf, 1);
+}
+
+static const struct file_operations modsign_enforce_ops = {
+ .read = modsign_enforce_read,
+ .llseek = generic_file_llseek,
+};
+
+static int __init securityfs_init(void)
+{
+ struct dentry *modsign_dir;
+ struct dentry *enforce;
+
+ modsign_dir = securityfs_create_dir("modsign", NULL);
+ if (IS_ERR(modsign_dir))
+ return -1;
+
+ enforce = securityfs_create_file("enforce",
+ S_IRUSR | S_IRGRP, modsign_dir,
+ NULL, &modsign_enforce_ops);
+ if (IS_ERR(enforce))
+ goto out;
+
+ return 0;
+out:
+ securityfs_remove(modsign_dir);
+
+ return -1;
+}
+#else /* !CONFIG_SECURITYFS */
+static int __init securityfs_init(void)
+{
+ return 0;
+}
+#endif
#else /* !CONFIG_MODULE_SIG */
static int module_sig_check(struct load_info *info, int flags)
{
return 0;
}
+
+static int __init securityfs_init(void)
+{
+ return 0;
+}
#endif /* !CONFIG_MODULE_SIG */
/* Sanity checks against invalid binaries, wrong arch, weird elf version. */
@@ -4395,8 +4444,14 @@ void module_layout(struct module *mod,
static int __init initialize_module(void)
{
+ int ret;
+
proc_modules_init();
+ ret = securityfs_init();
+ if (unlikely(ret))
+ return ret;
+
return 0;
}
module_init(initialize_module);
--
1.8.3.1
In order to disable the module validity enforcement, writing
a PKCS#7 signature corresponding the signed content '0' is
required. Given a simple way to archive this:
$ echo -n 0 > data
$ openssl smime -sign -nocerts -noattr -binary -in data \
-inkey <system_trusted_key> -signer <cert> -outform der \
-out data.sig
Note that the signing key must be a trust key located in
system trusted keyring. So even the root privilige cannot
simply disable the enforcement.
Signed-off-by: Jia Zhang <[email protected]>
---
kernel/module.c | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 114 insertions(+), 4 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
index 6b032577..16be198 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,6 +64,7 @@
#include <linux/bsearch.h>
#include <linux/dynamic_debug.h>
#include <linux/audit.h>
+#include <linux/verification.h>
#include <uapi/linux/module.h>
#include "module-internal.h"
@@ -288,6 +289,11 @@ bool is_module_sig_enforced(void)
}
EXPORT_SYMBOL(is_module_sig_enforced);
+static void set_module_sig_enforce(bool enforce)
+{
+ sig_enforce = enforce;
+}
+
/* Block module loading/unloading? */
int modules_disabled = 0;
core_param(nomodule, modules_disabled, bint, 0);
@@ -2796,6 +2802,61 @@ static int module_sig_check(struct load_info *info, int flags)
}
#ifdef CONFIG_SECURITYFS
+/*
+ * Check the intention of setting the enforcement policy.
+ *
+ * Return 1 if enabling the policy, or return 0 if disabling
+ * the policy. Note that the root privilege cannot simply
+ * disable the policy without the authentication given by a
+ * trusted key.
+ */
+static int check_enforce(char *buf, size_t count)
+{
+ u8 *p;
+
+ if (buf[0] == '1') {
+ if (count == 1 || (count == 2 && buf[1] == '\n'))
+ return 1;
+
+ return -EINVAL;
+ }
+
+ /*
+ * In order to disable the enforcement policy, a PKCS#7 signature
+ * is supplied.
+ *
+ * Assuming ASN.1 encoding supplied, the minimal length would be
+ * 4-byte header plus at least 256-byte payload.
+ */
+ if (count < 260)
+ return -EINVAL;
+
+ p = (u8 *)buf;
+
+ /* The primitive type must be a sequnce */
+ if (p[0] != 0x30 || p[1] != 0x82)
+ return -EINVAL;
+
+ /* Match up the length of the supplied buffer */
+ if (be16_to_cpup((__be16 *)(p + 2)) != count - 4)
+ return -EINVAL;
+
+ return 0;
+}
+
+/*
+ * Disable the enforceme and verify the supplied PKCS#7 signature.
+ * The signed content is simply the charactoror '0'.
+ */
+static int disable_enforce(void *pkcs7, size_t pkcs7_len)
+{
+ char data = '0';
+
+ return verify_pkcs7_signature(&data, sizeof(data), pkcs7, pkcs7_len,
+ NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
+ NULL, NULL);
+}
+
static ssize_t modsign_enforce_read(struct file *filp, char __user *ubuf,
size_t count, loff_t *offp)
{
@@ -2806,7 +2867,50 @@ static ssize_t modsign_enforce_read(struct file *filp, char __user *ubuf,
return simple_read_from_buffer(ubuf, count, offp, buf, 1);
}
-static const struct file_operations modsign_enforce_ops = {
+static ssize_t modsign_enforce_write(struct file *filp,
+ const char __user *ubuf,
+ size_t count, loff_t *offp)
+{
+ char *buf;
+ ssize_t ret;
+ size_t max_buf_size = 1 << MAX_ORDER;
+
+ if (*offp > 1)
+ return -EFBIG;
+
+ if (count > max_buf_size)
+ return -EFBIG;
+
+ buf = kmalloc(count, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ ret = simple_write_to_buffer(buf, count, offp, ubuf, count);
+ if (ret <= 0) {
+ kfree(buf);
+ return ret;
+ }
+
+ ret = check_enforce(buf, count);
+ if (is_module_sig_enforced() && !ret) {
+ ret = disable_enforce(buf, count);
+ if (!ret) {
+ set_module_sig_enforce(false);
+ pr_notice("Kernel module validity enforcement disabled\n");
+ ret = count;
+ }
+ } else if (!is_module_sig_enforced() && ret == 1) {
+ set_module_sig_enforce(true);
+ pr_notice("Kernel module validity enforcement enabled\n");
+ ret = count;
+ }
+
+ kfree(buf);
+
+ return ret;
+}
+
+static struct file_operations modsign_enforce_ops = {
.read = modsign_enforce_read,
.llseek = generic_file_llseek,
};
@@ -2815,14 +2919,20 @@ static int __init securityfs_init(void)
{
struct dentry *modsign_dir;
struct dentry *enforce;
+ umode_t mode;
modsign_dir = securityfs_create_dir("modsign", NULL);
if (IS_ERR(modsign_dir))
return -1;
- enforce = securityfs_create_file("enforce",
- S_IRUSR | S_IRGRP, modsign_dir,
- NULL, &modsign_enforce_ops);
+ mode = S_IRUSR | S_IRGRP;
+ if (!is_module_sig_enforced()) {
+ modsign_enforce_ops.write = modsign_enforce_write;
+ mode |= S_IWUSR;
+ }
+
+ enforce = securityfs_create_file("enforce", mode, modsign_dir, NULL,
+ &modsign_enforce_ops);
if (IS_ERR(enforce))
goto out;
--
1.8.3.1
This entry point currently includes the procfs initialization,
and will include a securityfs initialization.
Signed-off-by: Jia Zhang <[email protected]>
---
kernel/module.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/module.c b/kernel/module.c
index 003d0ab..79825ea 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4243,7 +4243,11 @@ static int __init proc_modules_init(void)
proc_create("modules", 0, NULL, &proc_modules_operations);
return 0;
}
-module_init(proc_modules_init);
+#else /* CONFIG_PROC_FS */
+static int __init proc_modules_init(void)
+{
+ return 0;
+}
#endif
/* Given an address, look for it in the module exception tables. */
@@ -4388,3 +4392,11 @@ void module_layout(struct module *mod,
}
EXPORT_SYMBOL(module_layout);
#endif
+
+static int __init initialize_module(void)
+{
+ proc_modules_init();
+
+ return 0;
+}
+module_init(initialize_module);
--
1.8.3.1
Call is_module_sig_enforced() instead.
Signed-off-by: Jia Zhang <[email protected]>
---
kernel/module.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/module.c b/kernel/module.c
index ad2d420..003d0ab 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2789,7 +2789,7 @@ static int module_sig_check(struct load_info *info, int flags)
}
/* Not having a signature is only an error if we're strict. */
- if (err == -ENOKEY && !sig_enforce)
+ if (err == -ENOKEY && !is_module_sig_enforced())
err = 0;
return err;
--
1.8.3.1
+++ Jia Zhang [08/03/18 12:26 +0800]:
>This patch series allows to disable module validity enforcement
>in runtime through /sys/kernel/security/modsign/enforce interface.
>
>Assuming CONFIG_MODULE_SIG_FORCE=y, here are the instructions to
>disable the validity enforcement.
>
># cat /sys/kernel/security/modsign/enforce
># echo -n 0 > data
># openssl smime -sign -nocerts -noattr -binary -in data \
> -inkey <system_trusted_key> -signer <cert> -outform der \
> -out /sys/kernel/security/modsign/enforce
>
>Now enable enforcement again on demand.
>
># echo 1 > /sys/kernel/security/modsign/enforce
>
>Changelog:
>v2:
>- Support to disable validity enforcement in runtime.
NAK - please use /sys/module/module/parameters/sig_enforce.
And I would rather keep this parameter bool_enable_only, plain and simple.
What use case do you have/why would you want to disable signature
enforcement - after having enabled it - during runtime? None of this
is explained nor justified in the cover letter.
Thanks,
Jessica
On 2018/3/12 下午9:28, Jessica Yu wrote:
> +++ Jia Zhang [08/03/18 12:26 +0800]:
>> This patch series allows to disable module validity enforcement
>> in runtime through /sys/kernel/security/modsign/enforce interface.
>>
>> Assuming CONFIG_MODULE_SIG_FORCE=y, here are the instructions to
>> disable the validity enforcement.
>>
>> # cat /sys/kernel/security/modsign/enforce
>> # echo -n 0 > data
>> # openssl smime -sign -nocerts -noattr -binary -in data \
>> -inkey <system_trusted_key> -signer <cert> -outform der \
>> -out /sys/kernel/security/modsign/enforce
>>
>> Now enable enforcement again on demand.
>>
>> # echo 1 > /sys/kernel/security/modsign/enforce
>>
>> Changelog:
>> v2:
>> - Support to disable validity enforcement in runtime.
>
> NAK - please use /sys/module/module/parameters/sig_enforce.
>
> And I would rather keep this parameter bool_enable_only, plain and simple.
> What use case do you have/why would you want to disable signature
> enforcement - after having enabled it - during runtime? None of this
> is explained nor justified in the cover letter.
Because there is no way to disable it such as module.no_sig_enforce when
MODULE_SIG_FORCE=y available unless re-compiling a kernel without this
enforcement. This is inconvenient a bit. IMA and SELinux both have
cmdline control, but modsign doesn't have.
Even we really have a module.no_sig_enforce in cmdline, runtime
disablement can be used to avoid machine reboot. Sometimes machine
reboot is expensive.
If you agree, I can implement the runtime disablement via
/sys/module/module/parameters/sig_enforce. Additionally, supporting
module.no_sig_enforce when MODULE_SIG_FORCE=y is another one to be
implemented.
Thanks,
Jia
>
> Thanks,
>
> Jessica