[RFC]selinux: Improving SELinux read/write performance
From: Yuichi Nakamura
Date: Thu Sep 06 2007 - 03:35:50 EST
Hello.
As I posted before in selinux list,
I found big overhead of SELinux in read/write on some CPUs,
and trying tuning.
There were discussion in previous threads.
Part 1:
http://marc.info/?t=118845343400001&r=1&w=2
Part 2:
http://marc.info/?t=118880749800004&r=1&w=2
I would like to RFC again about this topic.
1. Background
Look at benchmark result below.
lmbench simple read/write.
Big overhead exists especially on SH(SuperH) arch.
1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22
Base SELinux Overhead(%)
Simple read 1.10 1.24 12.3
Simple write 1.00 1.14 14.0
* Base: kernel compiled without SELinux support
2) Result for SH(SH4, SH7751R), kernel 2.6.22
Base SELinux Overhead(%)
Simple read 2.39 5.49 130.5
Simple write 2.07 5.10 146.6
# This result is a little different from previous threads,
# because I changed some kernel configs.
Overhead more than 100%
I also found about 70-90% overhead in ARM.
2. About patch
I found a overhead in selinux_file_permission function.
This is a function that is called in read/write calls,
and does SELinux permission check.
SELinux checks permission both in open and read/write time.
Stephen Smalley sugessted that we can usually skip permission check
in selinux_file_permission.
By this patch,
permission check in selinux_file_permssion is done only when
- sid of task has changed after file open
- sid of inode has changed after file open
- policy load or boolean change happen after file open
To detect these changes,
I added entries in file_security struct and saving these values at file open.
And to save sid of inode at the time of file open,
I had to add new LSM hook in __dentry_open function.
3. Benchmark after applying this patch
1) Result for x86(Pentium 4 2.6Ghz), kernel 2.6.22
Base SELinux Overhead(%)
Simple read 1.10 1.12 1.6(Before 12.3)
Simple write 1.00 1.03 3.6(Before 14.0)
2) Result for SH(SH4, SH7751R), kernel 2.6.22
Base SELinux Overhead(%)
Simple read 2.39 2.65 11.1(Before 130.5)
Simple write 2.07 2.28 10.5(Before 146.6)
Performance has improved a lot.
I want comments from community.
Signed-off-by: Yuichi Nakamura<ynakam@xxxxxxxxxxxxxx>
---
fs/open.c | 5 +++
include/linux/security.h | 11 +++++++
security/selinux/avc.c | 5 ++-
security/selinux/hooks.c | 54 +++++++++++++++++++++++++++++++++++++-
security/selinux/include/objsec.h | 3 ++
5 files changed, 76 insertions(+), 2 deletions(-)
diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/avc.c linux-2.6.22/security/selinux/avc.c
--- linux-2.6.22.orig/security/selinux/avc.c 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.22/security/selinux/avc.c 2007-09-06 14:33:35.000000000 +0900
@@ -123,6 +123,7 @@ DEFINE_PER_CPU(struct avc_cache_stats, a
#endif
static struct avc_cache avc_cache;
+u32 policy_seqno = 0;
static struct avc_callback_node *avc_callbacks;
static struct kmem_cache *avc_node_cachep;
@@ -431,8 +432,10 @@ static int avc_latest_notif_update(int s
ret = -EAGAIN;
}
} else {
- if (seqno > avc_cache.latest_notif)
+ if (seqno > avc_cache.latest_notif) {
avc_cache.latest_notif = seqno;
+ policy_seqno = seqno;
+ }
}
spin_unlock_irqrestore(¬if_lock, flag);
diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/hooks.c linux-2.6.22/security/selinux/hooks.c
--- linux-2.6.22.orig/security/selinux/hooks.c 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.22/security/selinux/hooks.c 2007-09-06 16:08:36.000000000 +0900
@@ -84,6 +84,7 @@
extern unsigned int policydb_loaded_version;
extern int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm);
extern int selinux_compat_net;
+extern u32 policy_seqno;
#ifdef CONFIG_SECURITY_SELINUX_DEVELOP
int selinux_enforcing = 0;
@@ -220,6 +221,8 @@ static int file_alloc_security(struct fi
fsec->file = file;
fsec->sid = tsec->sid;
+ fsec->tsid = tsec->sid;
+ fsec->pseqno = policy_seqno;
fsec->fown_sid = tsec->sid;
file->f_security = fsec;
@@ -2458,7 +2461,7 @@ static int selinux_inode_listsecurity(st
/* file security operations */
-static int selinux_file_permission(struct file *file, int mask)
+static int do_selinux_file_permission(struct file *file, int mask)
{
int rc;
struct inode *inode = file->f_path.dentry->d_inode;
@@ -2480,6 +2483,43 @@ static int selinux_file_permission(struc
return selinux_netlbl_inode_permission(inode, mask);
}
+static int selinux_file_permission(struct file *file, int mask)
+{
+ struct inode *inode = file->f_path.dentry->d_inode;
+ struct task_security_struct *tsec = current->security;
+ struct file_security_struct *fsec = file->f_security;
+ struct inode_security_struct *isec = inode->i_security;
+
+ if (!mask) {
+ /* No permission to check. Existence test. */
+ return 0;
+ }
+
+ if (tsec->sid != fsec->tsid) {
+ if (tsec->sid != fsec->sid) {
+ struct vfsmount *mnt = file->f_path.mnt;
+ struct dentry *dentry = file->f_path.dentry;
+ struct avc_audit_data ad;
+ int rc;
+ AVC_AUDIT_DATA_INIT(&ad, FS);
+ ad.u.fs.mnt = mnt;
+ ad.u.fs.dentry = dentry;
+ rc = avc_has_perm(tsec->sid, fsec->sid,
+ SECCLASS_FD,
+ FD__USE,
+ &ad);
+ if (rc)
+ return rc;
+ }
+ return do_selinux_file_permission(file, mask);
+ }
+
+ if (fsec->isid == isec->sid && fsec->pseqno == policy_seqno)
+ return selinux_netlbl_inode_permission(inode, mask);
+
+ return do_selinux_file_permission(file, mask);
+}
+
static int selinux_file_alloc_security(struct file *file)
{
return file_alloc_security(file);
@@ -2715,6 +2755,16 @@ static int selinux_file_receive(struct f
return file_has_perm(current, file, file_to_av(file));
}
+static int selinux_dentry_open(struct file *file, int flags)
+{
+ struct file_security_struct *fsec;
+ struct inode_security_struct *isec;
+ fsec = file->f_security;
+ isec = file->f_path.dentry->d_inode->i_security;
+ fsec->isid = isec->sid;
+ return 0;
+}
+
/* task security operations */
static int selinux_task_create(unsigned long clone_flags)
@@ -4780,6 +4830,8 @@ static struct security_operations selinu
.file_send_sigiotask = selinux_file_send_sigiotask,
.file_receive = selinux_file_receive,
+ .dentry_open = selinux_dentry_open,
+
.task_create = selinux_task_create,
.task_alloc_security = selinux_task_alloc_security,
.task_free_security = selinux_task_free_security,
diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/security/selinux/include/objsec.h linux-2.6.22/security/selinux/include/objsec.h
--- linux-2.6.22.orig/security/selinux/include/objsec.h 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.22/security/selinux/include/objsec.h 2007-09-06 14:58:11.000000000 +0900
@@ -53,6 +53,9 @@ struct file_security_struct {
struct file *file; /* back pointer to file object */
u32 sid; /* SID of open file description */
u32 fown_sid; /* SID of file owner (for SIGIO) */
+ u32 tsid; /* SID of task at the time of file open*/
+ u32 isid; /* SID of inode at the time of file open */
+ u32 pseqno; /* Policy seqno at the time of file open */
};
struct superblock_security_struct {
diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/fs/open.c linux-2.6.22/fs/open.c
--- linux-2.6.22.orig/fs/open.c 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.22/fs/open.c 2007-09-06 15:12:29.000000000 +0900
@@ -698,6 +698,11 @@ static struct file *__dentry_open(struct
if (!open && f->f_op)
open = f->f_op->open;
+
+ error = security_dentry_open(f, flags);
+ if (error)
+ goto cleanup_all;
+
if (open) {
error = open(inode, f);
if (error)
diff -purN -X linux-2.6.22/Documentation/dontdiff linux-2.6.22.orig/include/linux/security.h linux-2.6.22/include/linux/security.h
--- linux-2.6.22.orig/include/linux/security.h 2007-07-09 08:32:17.000000000 +0900
+++ linux-2.6.22/include/linux/security.h 2007-09-06 15:22:39.000000000 +0900
@@ -503,6 +503,11 @@ struct request_sock;
* @file contains the file structure being received.
* Return 0 if permission is granted.
*
+ * Security hook for dentry
+ *
+ * @dentry_open
+ * Check permission or get additional information before opening dentry.
+ *
* Security hooks for task operations.
*
* @task_create:
@@ -1253,6 +1258,7 @@ struct security_operations {
int (*file_send_sigiotask) (struct task_struct * tsk,
struct fown_struct * fown, int sig);
int (*file_receive) (struct file * file);
+ int (*dentry_open) (struct file *file, int flags);
int (*task_create) (unsigned long clone_flags);
int (*task_alloc_security) (struct task_struct * p);
@@ -1854,6 +1860,11 @@ static inline int security_file_receive
return security_ops->file_receive (file);
}
+static inline int security_dentry_open (struct file *file, int flags)
+{
+ return security_ops->dentry_open (file, flags);
+}
+
static inline int security_task_create (unsigned long clone_flags)
{
return security_ops->task_create (clone_flags);
Regards,
--
Yuichi Nakamura
Hitachi Software Engineering Co., Ltd.
Japan SELinux Users Group(JSELUG): http://www.selinux.gr.jp/
SELinux Policy Editor: http://seedit.sourceforge.net/
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