1 files changed, 60 insertions, 1 deletions

diff --git a/share/man/man4/capsicum.4 b/share/man/man4/capsicum.4
index 3c3eab5d798b..1de8e4531f4f 100644
--- a/share/man/man4/capsicum.4
+++ b/share/man/man4/capsicum.4
@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd January 3, 2024
+.Dd June 17, 2025
 .Dt CAPSICUM 4
 .Os
 .Sh NAME
@@ -37,6 +37,12 @@
 .Nm
 is a lightweight OS capability and sandbox framework implementing a hybrid
 capability system model.
+.Nm
+is designed to blend capabilities with UNIX.
+This approach achieves many of the benefits of least-privilege operation, while
+preserving existing UNIX APIs and performance, and presents application authors
+with an adoption path for capability-oriented design.
+.Pp
 Capabilities are unforgeable tokens of authority that can be delegated and must
 be presented to perform an action.
 .Nm
@@ -59,6 +65,34 @@ namespaces) is restricted; only explicitly delegated rights, referenced by
 memory mappings or file descriptors, may be used.
 Once set, the flag is inherited by future children processes, and may not be
 cleared.
+.Pp
+Access to system calls in capability mode is restricted: some system calls
+requiring global namespace access are unavailable, while others are
+constrained.
+For instance,
+.Xr sysctl 2
+can be used to query process-local information such as address space layout,
+but also to monitor a system’s network connections.
+.Xr sysctl 2
+is constrained by explicitly marking \(~~60 of over 15000 parameters as permitted
+in capability mode; all others are denied.
+.Pp
+The system calls which require constraints are
+.Xr sysctl 2 ,
+.Xr shm_open 2
+.Pq which is permitted to create anonymous memory objects but not named ones
+and the
+.Xr openat 2
+family of system calls.
+The
+.Xr openat 2
+calls already accept a file descriptor argument as the directory to perform the
+.Xr open 2 ,
+.Xr rename 2 ,
+etc. relative to; in capability mode the
+.Xr openat 2
+family of system calls are constrained so that they can only operate on
+objects “under” the provided file descriptor.
 .It capabilities
 Limit operations that can be called on file descriptors.
 For example, a file descriptor returned by
@@ -101,6 +135,20 @@ restrict access to global namespaces:
 Processes can only act upon their own process ID with syscalls such as
 .Xr cpuset_setaffinity 2 .
 .El
+.Pp
+.Fx
+provides some additional functionality to support application sandboxing that
+is not part of
+.Nm
+itself:
+.Bl -tag -width indent
+.It Xr capsicum_helpers 3
+A set of a inline functions which simplify modifying programs to use
+.Nm .
+.It Xr libcasper 3
+A library that provides services for sandboxed applications, such as operating
+on files specified on a command line or establishing network connections.
+.El
 .Sh SEE ALSO
 .Xr cap_enter 2 ,
 .Xr cap_fcntls_limit 2 ,
@@ -138,3 +186,14 @@ and
 .An Kris Kennaway Aq Mt kris@FreeBSD.org
 at Google, Inc., and
 .An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net .
+Portions of this manual page are drawn from
+.Rs
+.%A Robert N. M. Watson
+.%A Jonathan Anderson
+.%A Ben Laurie
+.%A Kris Kennaway
+.%T Capsicum: practical capabilities for UNIX
+.%J USENIX Security Symposium
+.%D August 2010
+.%O DOI: 10.5555/1929820.1929824
+.Re