DESCRIPTION
Each process on an illumos system has an associated set of security-flags which describe additional per-process security and exploit mitigation features which are enabled for that process.
There are four sets of these flags for each process, the effective set (abbreviated
E) are the set which currently apply to the process and are immutable. The inheritable set (abbreviated
I) are the flags which will become effective the next time the process calls one of the
exec(2) family of functions, and will be inherited as both the effective and inheritable sets by any child processes. The upper set (abbreviated
U) specify the maximal flags that a process can have in its inheritable set. The lower set (abbreviated
L) specify the minimal amount of flags that a process must have in its inheritable set. The inheritable set may be changed at any time, subject to permissions and the lower and upper sets.
To change the security-flags of a process one must have both permissions equivalent to those required to send a signal to the process and have the
PRIV_PROC_SECFLAGS privilege.
Currently available features are:
Address Space Layout Randomisation (
ASLR)
The base addresses of the stack, heap and shared library (including
ld.so) mappings are randomised, the bases of mapped regions other than those using
MAP_FIXED are randomised.
Currently, executable base addresses are
not randomised, due to which the mitigation provided by this feature is currently limited.
This flag may also be enabled by the presence of the
DT_SUNW_ASLR dynamic tag in the
.dynamic section of the executable file. If this tag has a value of 1, ASLR will be enabled. If the flag has a value of
0 ASLR will be disabled. If the tag is not present, the value of the ASLR flag will be inherited as normal.
Forbid mappings at NULL (
FORBIDNULLMAP)
Mappings with an address of 0 are forbidden, and return EINVAL rather than being honored.
Make the userspace stack non-executable (
NOEXECSTACK)
The stack will be mapped without executable permission, and attempts to execute it will fault.
System default security-flags are configured via properties on the
svc:/system/process-security service, which contains a boolean property per-flag in the
default,
lower and
upper, property groups. For example, to enable ASLR by default you would execute the following commands:
# svccfg -s svc:/system/process-security setprop default/aslr = true
This can be done by any user with the
solaris.smf.value.process-security authorization.
Since security-flags are strictly inherited, this will not take effect until the system or zone is next booted.