lockdown: Lock down /proc/kcore

Disallow access to /proc/kcore when the kernel is locked down to prevent
access to cryptographic data. This is limited to lockdown
confidentiality mode and is still permitted in integrity mode.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <jmorris@namei.org>

3 files changed, 7 insertions, 0 deletions

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index f5834488b67d..ee2c576cc94e 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -31,6 +31,7 @@
 #include <linux/ioport.h>
 #include <linux/memory.h>
 #include <linux/sched/task.h>
+#include <linux/security.h>
 #include <asm/sections.h>
 #include "internal.h"
 
@@ -545,6 +546,10 @@ out:
 
 static int open_kcore(struct inode *inode, struct file *filp)
 {
+        int ret = security_locked_down(LOCKDOWN_KCORE);
+
+        if (ret)
+                return ret;
         if (!capable(CAP_SYS_RAWIO))
                 return -EPERM;
 
diff --git a/include/linux/security.h b/include/linux/security.h
index d8db7ea4c4bf..669e8de5299d 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -116,6 +116,7 @@ enum lockdown_reason {
         LOCKDOWN_MODULE_PARAMETERS,
         LOCKDOWN_MMIOTRACE,
         LOCKDOWN_INTEGRITY_MAX,
+        LOCKDOWN_KCORE,
         LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 2eadbe0667e7..403b30357f75 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -31,6 +31,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
         [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
         [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
+        [LOCKDOWN_KCORE] = "/proc/kcore access",
         [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };