The new kernel module syscall appraises kernel modules based
on policy. If the IMA policy requires kernel module checking,
fallback to module signature enforcing for the existing syscall.
Without CONFIG_MODULE_SIG_FORCE enabled, the kernel module's
integrity is unknown, return -EACCES.
Changelog v1:
- Fix ima_module_check() return result (Tetsuo Handa)
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
With the addition of the new kernel module syscall, which defines two
arguments - a file descriptor to the kernel module and a pointer to a NULL
terminated string of module arguments - it is now possible to measure and
appraise kernel modules like any other file on the file system.
This patch adds support to measure and appraise kernel modules in an
extensible and consistent manner.
To support filesystems without extended attribute support, additional
patches could pass the signature as the first parameter.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Pull security subsystem updates from James Morris:
"Highlights:
- Integrity: add local fs integrity verification to detect offline
attacks
- Integrity: add digital signature verification
- Simple stacking of Yama with other LSMs (per LSS discussions)
- IBM vTPM support on ppc64
- Add new driver for Infineon I2C TIS TPM
- Smack: add rule revocation for subject labels"
Fixed conflicts with the user namespace support in kernel/auditsc.c and
security/integrity/ima/ima_policy.c.
* 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: (39 commits)
Documentation: Update git repository URL for Smack userland tools
ima: change flags container data type
Smack: setprocattr memory leak fix
Smack: implement revoking all rules for a subject label
Smack: remove task_wait() hook.
ima: audit log hashes
ima: generic IMA action flag handling
ima: rename ima_must_appraise_or_measure
audit: export audit_log_task_info
tpm: fix tpm_acpi sparse warning on different address spaces
samples/seccomp: fix 31 bit build on s390
ima: digital signature verification support
ima: add support for different security.ima data types
ima: add ima_inode_setxattr/removexattr function and calls
ima: add inode_post_setattr call
ima: replace iint spinblock with rwlock/read_lock
ima: allocating iint improvements
ima: add appraise action keywords and default rules
ima: integrity appraisal extension
vfs: move ima_file_free before releasing the file
...
Use kuid's in the IMA rules.
When reporting the current uid in audit logs use from_kuid
to get a usable value.
Cc: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This adds an 'audit' policy action which audit logs file measurements.
Changelog v6:
- use new action flag handling (Dmitry Kasatkin).
- removed whitespace (Mimi)
Changelog v5:
- use audit_log_untrustedstring.
Changelog v4:
- cleanup digest -> hash conversion.
- use filename rather than d_path in ima_audit_measurement.
Changelog v3:
- Use newly exported audit_log_task_info for logging pid/ppid/uid/etc.
- Update the ima_policy ABI documentation.
Changelog v2:
- Use 'audit' action rather than 'measure_and_audit' to permit
auditing in the absence of measuring..
Changelog v1:
- Initial posting.
Signed-off-by: Peter Moody <pmoody@google.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Make the IMA action flag handling generic in order to support
additional new actions, without requiring changes to the base
implementation. New actions, like audit logging, will only
need to modify the define statements.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
When AUDIT action support is added to the IMA,
ima_must_appraise_or_measure() does not reflect the real meaning anymore.
Rename it to ima_get_action().
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
This patch adds support for digital signature based integrity appraisal.
With this patch, 'security.ima' contains either the file data hash or
a digital signature of the file data hash. The file data hash provides
the security attribute of file integrity. In addition to file integrity,
a digital signature provides the security attribute of authenticity.
Unlike EVM, when the file metadata changes, the digital signature is
replaced with an HMAC, modification of the file data does not cause the
'security.ima' digital signature to be replaced with a hash. As a
result, after any modification, subsequent file integrity appraisals
would fail.
Although digitally signed files can be modified, but by not updating
'security.ima' to reflect these modifications, in essence digitally
signed files could be considered 'immutable'.
IMA uses a different keyring than EVM. While the EVM keyring should not
be updated after initialization and locked, the IMA keyring should allow
updating or adding new keys when upgrading or installing packages.
Changelog v4:
- Change IMA_DIGSIG to hex equivalent
Changelog v3:
- Permit files without any 'security.ima' xattr to be labeled properly.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
IMA-appraisal currently verifies the integrity of a file based on a
known 'good' measurement value. This patch reserves the first byte
of 'security.ima' as a place holder for the type of method used for
verifying file data integrity.
Changelog v1:
- Use the newly defined 'struct evm_ima_xattr_data'
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Based on xattr_permission comments, the restriction to modify 'security'
xattr is left up to the underlying fs or lsm. Ensure that not just anyone
can modify or remove 'security.ima'.
Changelog v1:
- Unless IMA-APPRAISE is configured, use stub ima_inode_removexattr()/setxattr()
functions. (Moved ima_inode_removexattr()/setxattr() to ima_appraise.c)
Changelog:
- take i_mutex to fix locking (Dmitry Kasatkin)
- ima_reset_appraise_flags should only be called when modifying or
removing the 'security.ima' xattr. Requires CAP_SYS_ADMIN privilege.
(Incorporated fix from Roberto Sassu)
- Even if allowed to update security.ima, reset the appraisal flags,
forcing re-appraisal.
- Replace CAP_MAC_ADMIN with CAP_SYS_ADMIN
- static inline ima_inode_setxattr()/ima_inode_removexattr() stubs
- ima_protect_xattr should be static
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
With IMA-appraisal's removal of the iint mutex and taking the i_mutex
instead, allocating the iint becomes a lot simplier, as we don't need
to be concerned with two processes racing to allocate the iint. This
patch cleans up and improves performance for allocating the iint.
- removed redundant double i_mutex locking
- combined iint allocation with tree search
Changelog v2:
- removed the rwlock/read_lock changes from this patch
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Unlike the IMA measurement policy, the appraise policy can not be dependent
on runtime process information, such as the task uid, as the 'security.ima'
xattr is written on file close and must be updated each time the file changes,
regardless of the current task uid.
This patch extends the policy language with 'fowner', defines an appraise
policy, which appraises all files owned by root, and defines 'ima_appraise_tcb',
a new boot command line option, to enable the appraise policy.
Changelog v3:
- separate the measure from the appraise rules in order to support measuring
without appraising and appraising without measuring.
- change appraisal default for filesystems without xattr support to fail
- update default appraise policy for cgroups
Changelog v1:
- don't appraise RAMFS (Dmitry Kasatkin)
- merged rest of "ima: ima_must_appraise_or_measure API change" commit
(Dmtiry Kasatkin)
ima_must_appraise_or_measure() called ima_match_policy twice, which
searched the policy for a matching rule. Once for a matching measurement
rule and subsequently for an appraisal rule. Searching the policy twice
is unnecessary overhead, which could be noticeable with a large policy.
The new version of ima_must_appraise_or_measure() does everything in a
single iteration using a new version of ima_match_policy(). It returns
IMA_MEASURE, IMA_APPRAISE mask.
With the use of action mask only one efficient matching function
is enough. Removed other specific versions of matching functions.
Changelog:
- change 'owner' to 'fowner' to conform to the new LSM conditions posted by
Roberto Sassu.
- fix calls to ima_log_string()
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
IMA currently maintains an integrity measurement list used to assert the
integrity of the running system to a third party. The IMA-appraisal
extension adds local integrity validation and enforcement of the
measurement against a "good" value stored as an extended attribute
'security.ima'. The initial methods for validating 'security.ima' are
hashed based, which provides file data integrity, and digital signature
based, which in addition to providing file data integrity, provides
authenticity.
This patch creates and maintains the 'security.ima' xattr, containing
the file data hash measurement. Protection of the xattr is provided by
EVM, if enabled and configured.
Based on policy, IMA calls evm_verifyxattr() to verify a file's metadata
integrity and, assuming success, compares the file's current hash value
with the one stored as an extended attribute in 'security.ima'.
Changelov v4:
- changed iint cache flags to hex values
Changelog v3:
- change appraisal default for filesystems without xattr support to fail
Changelog v2:
- fix audit msg 'res' value
- removed unused 'ima_appraise=' values
Changelog v1:
- removed unused iint mutex (Dmitry Kasatkin)
- setattr hook must not reset appraised (Dmitry Kasatkin)
- evm_verifyxattr() now differentiates between no 'security.evm' xattr
(INTEGRITY_NOLABEL) and no EVM 'protected' xattrs included in the
'security.evm' (INTEGRITY_NOXATTRS).
- replace hash_status with ima_status (Dmitry Kasatkin)
- re-initialize slab element ima_status on free (Dmitry Kasatkin)
- include 'security.ima' in EVM if CONFIG_IMA_APPRAISE, not CONFIG_IMA
- merged half "ima: ima_must_appraise_or_measure API change" (Dmitry Kasatkin)
- removed unnecessary error variable in process_measurement() (Dmitry Kasatkin)
- use ima_inode_post_setattr() stub function, if IMA_APPRAISE not configured
(moved ima_inode_post_setattr() to ima_appraise.c)
- make sure ima_collect_measurement() can read file
Changelog:
- add 'iint' to evm_verifyxattr() call (Dimitry Kasatkin)
- fix the race condition between chmod, which takes the i_mutex and then
iint->mutex, and ima_file_free() and process_measurement(), which take
the locks in the reverse order, by eliminating iint->mutex. (Dmitry Kasatkin)
- cleanup of ima_appraise_measurement() (Dmitry Kasatkin)
- changes as a result of the iint not allocated for all regular files, but
only for those measured/appraised.
- don't try to appraise new/empty files
- expanded ima_appraisal description in ima/Kconfig
- IMA appraise definitions required even if IMA_APPRAISE not enabled
- add return value to ima_must_appraise() stub
- unconditionally set status = INTEGRITY_PASS *after* testing status,
not before. (Found by Joe Perches)
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
IMA auditing code was compiled even when CONFIG_AUDIT was not enabled.
This patch compiles auditing code only when possible and enabled.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Set ima_initialized only if initialization was successful.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
IMA cannot be used as module and does not need __exit functions.
Removed them.
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
The IMA measurement list contains filename hints, which can be
ambigious without the full pathname. This patch replaces the
filename hint with the full pathname, simplifying for userspace
the correlating of file hash measurements with files.
Change log v1:
- Revert to short filenames, when full pathname is longer than IMA
measurement buffer size. (Based on Dmitry's review)
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
When IMA was first upstreamed, the bprm filename and interp were
always the same. Currently, the bprm->filename and bprm->interp
are the same, except for when only bprm->interp contains the
interpreter name. So instead of using the bprm->filename as
the IMA filename hint in the measurement list, we could replace
it with bprm->interp, but this feels too fragil.
The following patch is not much better, but at least there is some
indication that sometimes we're passing the filename and other times
the interpreter name.
Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Fix IMA kconfig warning on non-X86 architectures:
warning: (IMA) selects TCG_TIS which has unmet direct dependencies
(TCG_TPM && X86)
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
The audit res field ususally indicates success with a 1 and 0 for a
failure. So make IMA do it the same way.
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
Fix ima_policy.c sparse "warning: dereference of noderef expression"
message, by accessing cred->uid using current_cred().
Changelog v1:
- Change __cred to just cred (based on David Howell's comment)
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
The use of s_id should go through the untrusted string path, just to be
extra careful.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Mimi Zohar <zohar@us.ibm.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Info about new measurements are cached in the iint for performance. When
the inode is flushed from cache, the associated iint is flushed as well.
Subsequent access to the inode will cause the inode to be re-measured and
will attempt to add a duplicate entry to the measurement list.
This patch frees the duplicate measurement memory, fixing a memory leak.
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Cc: stable@vger.kernel.org
* 'for-linus' of git://github.com/richardweinberger/linux: (90 commits)
um: fix ubd cow size
um: Fix kmalloc argument order in um/vdso/vma.c
um: switch to use of drivers/Kconfig
UserModeLinux-HOWTO.txt: fix a typo
UserModeLinux-HOWTO.txt: remove ^H characters
um: we need sys/user.h only on i386
um: merge delay_{32,64}.c
um: distribute exports to where exported stuff is defined
um: kill system-um.h
um: generic ftrace.h will do...
um: segment.h is x86-only and needed only there
um: asm/pda.h is not needed anymore
um: hw_irq.h can go generic as well
um: switch to generic-y
um: clean Kconfig up a bit
um: a couple of missing dependencies...
um: kill useless argument of free_chan() and free_one_chan()
um: unify ptrace_user.h
um: unify KSTK_...
um: fix gcov build breakage
...
Fixes sparse warnings:
security/integrity/ima/ima_main.c:105:6: warning: symbol 'ima_file_free' was not declared. Should it be static?
security/integrity/ima/ima_main.c:167:5: warning: symbol 'ima_file_mmap' was not declared. Should it be static?
security/integrity/ima/ima_main.c:192:5: warning: symbol 'ima_bprm_check' was not declared. Should it be static?
security/integrity/ima/ima_main.c:211:5: warning: symbol 'ima_file_check' was not declared. Should it be static?
Signed-off-by: James Morris <jmorris@namei.org>
Fixes sparse warning:
security/integrity/ima/ima_fs.c:290:5: warning: symbol 'ima_open_policy' was not declared. Should it be static?
Signed-off-by: James Morris <jmorris@namei.org>
Move the inode integrity data(iint) management up to the integrity directory
in order to share the iint among the different integrity models.
Changelog:
- don't define MAX_DIGEST_SIZE
- rename several globally visible 'ima_' prefixed functions, structs,
locks, etc to 'integrity_'
- replace '20' with SHA1_DIGEST_SIZE
- reflect location change in appropriate Kconfig and Makefiles
- remove unnecessary initialization of iint_initialized to 0
- rebased on current ima_iint.c
- define integrity_iint_store/lock as static
There should be no other functional changes.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>
The original ima_must_measure() function based its results on cached
iint information, which required an iint be allocated for all files.
Currently, an iint is allocated only for files in policy. As a result,
for those files in policy, ima_must_measure() is now called twice: once
to determine if the inode is in the measurement policy and, the second
time, to determine if it needs to be measured/re-measured.
The second call to ima_must_measure() unnecessarily checks to see if
the file is in policy. As we already know the file is in policy, this
patch removes the second unnecessary call to ima_must_measure(), removes
the vestige iint parameter, and just checks the iint directly to determine
if the inode has been measured or needs to be measured/re-measured.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Eric Paris <eparis@redhat.com>
Now that i_readcount is maintained by the VFS layer, remove the
imbalance checking in IMA. Cleans up the IMA code nicely.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Eric Paris <eparis@redhat.com>
ima_counts_get() updated the readcount and invalidated the PCR,
as necessary. Only update the i_readcount in the VFS layer.
Move the PCR invalidation checks to ima_file_check(), where it
belongs.
Maintaining the i_readcount in the VFS layer, will allow other
subsystems to use i_readcount.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Eric Paris <eparis@redhat.com>
If security_filter_rule_init() doesn't return a rule, then not everything
is as fine as the return code implies.
This bug only occurs when the LSM (eg. SELinux) is disabled at runtime.
Adding an empty LSM rule causes ima_match_rules() to always succeed,
ignoring any remaining rules.
default IMA TCB policy:
# PROC_SUPER_MAGIC
dont_measure fsmagic=0x9fa0
# SYSFS_MAGIC
dont_measure fsmagic=0x62656572
# DEBUGFS_MAGIC
dont_measure fsmagic=0x64626720
# TMPFS_MAGIC
dont_measure fsmagic=0x01021994
# SECURITYFS_MAGIC
dont_measure fsmagic=0x73636673
< LSM specific rule >
dont_measure obj_type=var_log_t
measure func=BPRM_CHECK
measure func=FILE_MMAP mask=MAY_EXEC
measure func=FILE_CHECK mask=MAY_READ uid=0
Thus without the patch, with the boot parameters 'tcb selinux=0', adding
the above 'dont_measure obj_type=var_log_t' rule to the default IMA TCB
measurement policy, would result in nothing being measured. The patch
prevents the default TCB policy from being replaced.
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Cc: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: David Safford <safford@watson.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Current logic looks like this:
rc = ima_must_measure(NULL, inode, MAY_READ, FILE_CHECK);
if (rc < 0)
goto out;
if (mode & FMODE_WRITE) {
if (inode->i_readcount)
send_tomtou = true;
goto out;
}
if (atomic_read(&inode->i_writecount) > 0)
send_writers = true;
Lets assume we have a policy which states that all files opened for read
by root must be measured.
Lets assume the file has permissions 777.
Lets assume that root has the given file open for read.
Lets assume that a non-root process opens the file write.
The non-root process will get to ima_counts_get() and will check the
ima_must_measure(). Since it is not supposed to measure it will goto
out.
We should check the i_readcount no matter what since we might be causing
a ToMToU voilation!
This is close to correct, but still not quite perfect. The situation
could have been that root, which was interested in the mesurement opened
and closed the file and another process which is not interested in the
measurement is the one holding the i_readcount ATM. This is just overly
strict on ToMToU violations, which is better than not strict enough...
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently for every removed inode IMA must take a global lock and search
the IMA rbtree looking for an associated integrity structure. Instead
we explicitly mark an inode when we add an integrity structure so we
only have to take the global lock and do the removal if it exists.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Since finding a struct ima_iint_cache requires a valid struct inode, and
the struct ima_iint_cache is supposed to have the same lifetime as a
struct inode (technically they die together but don't need to be created
at the same time) we don't have to worry about the ima_iint_cache
outliving or dieing before the inode. So the refcnt isn't useful. Just
get rid of it and free the structure when the inode is freed.
Signed-off-by: Eric Paris <eapris@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
IMA always allocates an integrity structure to hold information about
every inode, but only needed this structure to track the number of
readers and writers currently accessing a given inode. Since that
information was moved into struct inode instead of the integrity struct
this patch stops allocating the integrity stucture until it is needed.
Thus greatly reducing memory usage.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
IMA currently allocated an inode integrity structure for every inode in
core. This stucture is about 120 bytes long. Most files however
(especially on a system which doesn't make use of IMA) will never need
any of this space. The problem is that if IMA is enabled we need to
know information about the number of readers and the number of writers
for every inode on the box. At the moment we collect that information
in the per inode iint structure and waste the rest of the space. This
patch moves those counters into the struct inode so we can eventually
stop allocating an IMA integrity structure except when absolutely
needed.
This patch does the minimum needed to move the location of the data.
Further cleanups, especially the location of counter updates, may still
be possible.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
IMA tracks the number of struct files which are holding a given inode
readonly and the number which are holding the inode write or r/w. It
needs this information so when a new reader or writer comes in it can
tell if this new file will be able to invalidate results it already made
about existing files.
aka if a task is holding a struct file open RO, IMA measured the file
and recorded those measurements and then a task opens the file RW IMA
needs to note in the logs that the old measurement may not be correct.
It's called a "Time of Measure Time of Use" (ToMToU) issue. The same is
true is a RO file is opened to an inode which has an open writer. We
cannot, with any validity, measure the file in question since it could
be changing.
This patch attempts to use the i_writecount field to track writers. The
i_writecount field actually embeds more information in it's value than
IMA needs but it should work for our purposes and allow us to shrink the
struct inode even more.
Signed-off-by: Eric Paris <eparis@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Mimi Zohar