diff mbox

[v5,3/8] ima: based on policy require signed kexec kernel images

Message ID 1530542283-26145-4-git-send-email-zohar@linux.vnet.ibm.com (mailing list archive)
State New, archived
Headers show

Commit Message

Mimi Zohar July 2, 2018, 2:37 p.m. UTC
The original kexec_load syscall can not verify file signatures, nor can
the kexec image be measured.  Based on policy, deny the kexec_load
syscall.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: David Howells <dhowells@redhat.com>

---
Changelog v3:
- use switch/case

 include/linux/ima.h                 |  7 +++++++
 security/integrity/ima/ima.h        |  1 +
 security/integrity/ima/ima_main.c   | 27 +++++++++++++++++++++++++++
 security/integrity/ima/ima_policy.c |  2 ++
 security/security.c                 |  7 ++++++-
 5 files changed, 43 insertions(+), 1 deletion(-)

Comments

Jay Freyensee July 2, 2018, 6:31 p.m. UTC | #1
On 7/2/18 7:37 AM, Mimi Zohar wrote:
> The original kexec_load syscall can not verify file signatures, nor can
> the kexec image be measured.  Based on policy, deny the kexec_load
> syscall.


Curiosity question: I thought kexec_load() syscall was used to load a 
crashdump?  If this is true, how would this work if kexec_load() is 
being denied?  I don't think I'd want to be hindered in cases where I'm 
trying to diagnose a crash.

Thanks,
Jay


> Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Luis R. Rodriguez <mcgrof@kernel.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: David Howells <dhowells@redhat.com>
>
> ---
> Changelog v3:
> - use switch/case
>
>   include/linux/ima.h                 |  7 +++++++
>   security/integrity/ima/ima.h        |  1 +
>   security/integrity/ima/ima_main.c   | 27 +++++++++++++++++++++++++++
>   security/integrity/ima/ima_policy.c |  2 ++
>   security/security.c                 |  7 ++++++-
>   5 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 0e4647e0eb60..84806b54b50a 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -11,6 +11,7 @@
>   #define _LINUX_IMA_H
>   
>   #include <linux/fs.h>
> +#include <linux/security.h>
>   #include <linux/kexec.h>
>   struct linux_binprm;
>   
> @@ -19,6 +20,7 @@ extern int ima_bprm_check(struct linux_binprm *bprm);
>   extern int ima_file_check(struct file *file, int mask, int opened);
>   extern void ima_file_free(struct file *file);
>   extern int ima_file_mmap(struct file *file, unsigned long prot);
> +extern int ima_load_data(enum kernel_load_data_id id);
>   extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
>   extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
>   			      enum kernel_read_file_id id);
> @@ -49,6 +51,11 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
>   	return 0;
>   }
>   
> +static inline int ima_load_data(enum kernel_load_data_id id)
> +{
> +	return 0;
> +}
> +
>   static inline int ima_read_file(struct file *file, enum kernel_read_file_id id)
>   {
>   	return 0;
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 2ab1affffa36..588e4813370c 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -232,6 +232,7 @@ int ima_policy_show(struct seq_file *m, void *v);
>   #define IMA_APPRAISE_MODULES	0x08
>   #define IMA_APPRAISE_FIRMWARE	0x10
>   #define IMA_APPRAISE_POLICY	0x20
> +#define IMA_APPRAISE_KEXEC	0x40
>   
>   #ifdef CONFIG_IMA_APPRAISE
>   int ima_appraise_measurement(enum ima_hooks func,
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index dca44cf7838e..71fecfef0939 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -496,6 +496,33 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
>   				   MAY_READ, func, 0);
>   }
>   
> +/**
> + * ima_load_data - appraise decision based on policy
> + * @id: kernel load data caller identifier
> + *
> + * Callers of this LSM hook can not measure, appraise, or audit the
> + * data provided by userspace.  Enforce policy rules requring a file
> + * signature (eg. kexec'ed kernel image).
> + *
> + * For permission return 0, otherwise return -EACCES.
> + */
> +int ima_load_data(enum kernel_load_data_id id)
> +{
> +	if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
> +		return 0;
> +
> +	switch (id) {
> +	case LOADING_KEXEC_IMAGE:
> +		if (ima_appraise & IMA_APPRAISE_KEXEC) {
> +			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
> +			return -EACCES;	/* INTEGRITY_UNKNOWN */
> +		}
> +	default:
> +		break;
> +	}
> +	return 0;
> +}
> +
>   static int __init init_ima(void)
>   {
>   	int error;
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 7f4a4de7e831..ebfb389b79df 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -448,6 +448,8 @@ static int ima_appraise_flag(enum ima_hooks func)
>   		return IMA_APPRAISE_FIRMWARE;
>   	else if (func == POLICY_CHECK)
>   		return IMA_APPRAISE_POLICY;
> +	else if (func == KEXEC_KERNEL_CHECK)
> +		return IMA_APPRAISE_KEXEC;
>   	return 0;
>   }
>   
> diff --git a/security/security.c b/security/security.c
> index 05fe5b1932d7..7b870df0a335 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1063,7 +1063,12 @@ EXPORT_SYMBOL_GPL(security_kernel_post_read_file);
>   
>   int security_kernel_load_data(enum kernel_load_data_id id)
>   {
> -	return call_int_hook(kernel_load_data, 0, id);
> +	int ret;
> +
> +	ret = call_int_hook(kernel_load_data, 0, id);
> +	if (ret)
> +		return ret;
> +	return ima_load_data(id);
>   }
>   
>   int security_task_fix_setuid(struct cred *new, const struct cred *old,
Mimi Zohar July 3, 2018, 1:07 p.m. UTC | #2
On Mon, 2018-07-02 at 11:31 -0700, J Freyensee wrote:
> 
> On 7/2/18 7:37 AM, Mimi Zohar wrote:
> > The original kexec_load syscall can not verify file signatures, nor can
> > the kexec image be measured.  Based on policy, deny the kexec_load
> > syscall.
> 
> 
> Curiosity question: I thought kexec_load() syscall was used to load a 
> crashdump?

kexec is used to collect the memory used to analyze the crash dump.

> If this is true, how would this work if kexec_load() is 
> being denied?  I don't think I'd want to be hindered in cases where I'm 
> trying to diagnose a crash.

For trusted & secure boot, we need a full measurement list and
signature chain of trust rooted in HW.  Permitting kexec_load would
break these chains of trust.

Permitting/denying kexec_load is based on a runtime IMA policy.  Patch
6/8 "ima: add build time policy", in this patch set, introduces the
concept of a build time policy.  With these patches, you could
configure your kernel and/or load an IMA policy permitting kexec_load.

Mimi
diff mbox

Patch

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 0e4647e0eb60..84806b54b50a 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -11,6 +11,7 @@ 
 #define _LINUX_IMA_H
 
 #include <linux/fs.h>
+#include <linux/security.h>
 #include <linux/kexec.h>
 struct linux_binprm;
 
@@ -19,6 +20,7 @@  extern int ima_bprm_check(struct linux_binprm *bprm);
 extern int ima_file_check(struct file *file, int mask, int opened);
 extern void ima_file_free(struct file *file);
 extern int ima_file_mmap(struct file *file, unsigned long prot);
+extern int ima_load_data(enum kernel_load_data_id id);
 extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
 extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
 			      enum kernel_read_file_id id);
@@ -49,6 +51,11 @@  static inline int ima_file_mmap(struct file *file, unsigned long prot)
 	return 0;
 }
 
+static inline int ima_load_data(enum kernel_load_data_id id)
+{
+	return 0;
+}
+
 static inline int ima_read_file(struct file *file, enum kernel_read_file_id id)
 {
 	return 0;
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 2ab1affffa36..588e4813370c 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -232,6 +232,7 @@  int ima_policy_show(struct seq_file *m, void *v);
 #define IMA_APPRAISE_MODULES	0x08
 #define IMA_APPRAISE_FIRMWARE	0x10
 #define IMA_APPRAISE_POLICY	0x20
+#define IMA_APPRAISE_KEXEC	0x40
 
 #ifdef CONFIG_IMA_APPRAISE
 int ima_appraise_measurement(enum ima_hooks func,
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index dca44cf7838e..71fecfef0939 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -496,6 +496,33 @@  int ima_post_read_file(struct file *file, void *buf, loff_t size,
 				   MAY_READ, func, 0);
 }
 
+/**
+ * ima_load_data - appraise decision based on policy
+ * @id: kernel load data caller identifier
+ *
+ * Callers of this LSM hook can not measure, appraise, or audit the
+ * data provided by userspace.  Enforce policy rules requring a file
+ * signature (eg. kexec'ed kernel image).
+ *
+ * For permission return 0, otherwise return -EACCES.
+ */
+int ima_load_data(enum kernel_load_data_id id)
+{
+	if ((ima_appraise & IMA_APPRAISE_ENFORCE) != IMA_APPRAISE_ENFORCE)
+		return 0;
+
+	switch (id) {
+	case LOADING_KEXEC_IMAGE:
+		if (ima_appraise & IMA_APPRAISE_KEXEC) {
+			pr_err("impossible to appraise a kernel image without a file descriptor; try using kexec_file_load syscall.\n");
+			return -EACCES;	/* INTEGRITY_UNKNOWN */
+		}
+	default:
+		break;
+	}
+	return 0;
+}
+
 static int __init init_ima(void)
 {
 	int error;
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 7f4a4de7e831..ebfb389b79df 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -448,6 +448,8 @@  static int ima_appraise_flag(enum ima_hooks func)
 		return IMA_APPRAISE_FIRMWARE;
 	else if (func == POLICY_CHECK)
 		return IMA_APPRAISE_POLICY;
+	else if (func == KEXEC_KERNEL_CHECK)
+		return IMA_APPRAISE_KEXEC;
 	return 0;
 }
 
diff --git a/security/security.c b/security/security.c
index 05fe5b1932d7..7b870df0a335 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1063,7 +1063,12 @@  EXPORT_SYMBOL_GPL(security_kernel_post_read_file);
 
 int security_kernel_load_data(enum kernel_load_data_id id)
 {
-	return call_int_hook(kernel_load_data, 0, id);
+	int ret;
+
+	ret = call_int_hook(kernel_load_data, 0, id);
+	if (ret)
+		return ret;
+	return ima_load_data(id);
 }
 
 int security_task_fix_setuid(struct cred *new, const struct cred *old,