diff mbox series

[V34,06/29] kexec_load: Disable at runtime if the kernel is locked down

Message ID 20190622000358.19895-7-matthewgarrett@google.com (mailing list archive)
State New, archived
Headers show
Series Lockdown as an LSM | expand

Commit Message

Matthew Garrett June 22, 2019, 12:03 a.m. UTC
From: Matthew Garrett <mjg59@srcf.ucam.org>

The kexec_load() syscall permits the loading and execution of arbitrary
code in ring 0, which is something that lock-down is meant to prevent. It
makes sense to disable kexec_load() in this situation.

This does not affect kexec_file_load() syscall which can check for a
signature on the image to be booted.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Acked-by: Dave Young <dyoung@redhat.com>
cc: kexec@lists.infradead.org
---
 include/linux/security.h     | 1 +
 kernel/kexec.c               | 8 ++++++++
 security/lockdown/lockdown.c | 1 +
 3 files changed, 10 insertions(+)

Comments

Kees Cook June 22, 2019, 11:52 p.m. UTC | #1
On Fri, Jun 21, 2019 at 05:03:35PM -0700, Matthew Garrett wrote:
> From: Matthew Garrett <mjg59@srcf.ucam.org>
> 
> The kexec_load() syscall permits the loading and execution of arbitrary
> code in ring 0, which is something that lock-down is meant to prevent. It
> makes sense to disable kexec_load() in this situation.
> 
> This does not affect kexec_file_load() syscall which can check for a
> signature on the image to be booted.
> 
> Signed-off-by: David Howells <dhowells@redhat.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> Signed-off-by: Matthew Garrett <mjg59@google.com>
> Acked-by: Dave Young <dyoung@redhat.com>
> cc: kexec@lists.infradead.org
> ---
>  include/linux/security.h     | 1 +
>  kernel/kexec.c               | 8 ++++++++
>  security/lockdown/lockdown.c | 1 +
>  3 files changed, 10 insertions(+)
> 
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 200175c8605a..00a31ab2e5ba 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -84,6 +84,7 @@ enum lockdown_reason {
>  	LOCKDOWN_NONE,
>  	LOCKDOWN_MODULE_SIGNATURE,
>  	LOCKDOWN_DEV_MEM,
> +	LOCKDOWN_KEXEC,
>  	LOCKDOWN_INTEGRITY_MAX,
>  	LOCKDOWN_CONFIDENTIALITY_MAX,
>  };
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 68559808fdfa..ec3f07a4b1c0 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -207,6 +207,14 @@ static inline int kexec_load_check(unsigned long nr_segments,
>  	if (result < 0)
>  		return result;
>  
> +	/*
> +	 * kexec can be used to circumvent module loading restrictions, so
> +	 * prevent loading in that case
> +	 */
> +	result = security_locked_down(LOCKDOWN_KEXEC);
> +	if (result)
> +		return result;
> +
>  	/*
>  	 * Verify we have a legal set of flags
>  	 * This leaves us room for future extensions.
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 565c87451f0f..08fcd8116db3 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -20,6 +20,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>  	[LOCKDOWN_NONE] = "none",
>  	[LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
>  	[LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
> +	[LOCKDOWN_KEXEC] = "kexec of unsigned images",
>  	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
>  	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
>  };
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
>
diff mbox series

Patch

diff --git a/include/linux/security.h b/include/linux/security.h
index 200175c8605a..00a31ab2e5ba 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -84,6 +84,7 @@  enum lockdown_reason {
 	LOCKDOWN_NONE,
 	LOCKDOWN_MODULE_SIGNATURE,
 	LOCKDOWN_DEV_MEM,
+	LOCKDOWN_KEXEC,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 68559808fdfa..ec3f07a4b1c0 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -207,6 +207,14 @@  static inline int kexec_load_check(unsigned long nr_segments,
 	if (result < 0)
 		return result;
 
+	/*
+	 * kexec can be used to circumvent module loading restrictions, so
+	 * prevent loading in that case
+	 */
+	result = security_locked_down(LOCKDOWN_KEXEC);
+	if (result)
+		return result;
+
 	/*
 	 * Verify we have a legal set of flags
 	 * This leaves us room for future extensions.
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 565c87451f0f..08fcd8116db3 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -20,6 +20,7 @@  static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_NONE] = "none",
 	[LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading",
 	[LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port",
+	[LOCKDOWN_KEXEC] = "kexec of unsigned images",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };