1.\" Copyright (c) 2022 Klara Systems 2.\" 3.\" This software was developed by Mitchell Horne <mhorne@FreeBSD.org> 4.\" under sponsorship from Juniper Networks and Klara Systems. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.Dd June 29, 2022 28.Dt MAC_DDB 4 29.Os 30.Sh NAME 31.Nm mac_ddb 32.Nd "Restricted kernel debugger interface policy" 33.Sh SYNOPSIS 34To compile the ddb policy 35into your kernel, place the following lines in your kernel 36configuration file: 37.Bd -ragged -offset indent 38.Cd "options MAC" 39.Cd "options MAC_DDB" 40.Ed 41.Pp 42Alternately, to load the ddb module at boot time, place the following line 43in your kernel configuration file: 44.Bd -ragged -offset indent 45.Cd "options MAC" 46.Ed 47.Pp 48and in 49.Xr loader.conf 5 : 50.Bd -literal -offset indent 51mac_ddb_load="YES" 52.Ed 53.Sh DESCRIPTION 54The 55.Nm 56policy module implements a MAC policy which restricts the set of commands that 57can be used at the 58.Xr ddb 4 59command prompt. 60The subset of permitted commands is limited to those which do not read or write 61to arbitrary memory locations. 62This is done to deter the possible extraction of system secrets while still 63allowing enough debugger functionality to diagnose a kernel panic. 64For example, the 65.Ic trace 66or 67.Ic show registers 68commands are allowed by this policy, but 69.Ic show Cm buffer Ar addr 70is not. 71.Pp 72All debugger commands that are declared with the 73.Va DB_CMD_MEMSAFE 74flag are allowed by 75.Nm . 76The policy provides validation functions to conditionally allow some additional 77commands, based on the user provided arguments. 78.Pp 79When loaded, the 80.Nm 81policy also ensures that only the 82.Xr ddb 4 83debugger backend may be executed; 84.Xr gdb 4 85may not. 86.Ss Label Format 87No labels are defined for 88.Nm . 89.Sh SEE ALSO 90.Xr ddb 4 , 91.Xr mac 4 , 92.Xr mac_biba 4 , 93.Xr mac_bsdextended 4 , 94.Xr mac_ifoff 4 , 95.Xr mac_lomac 4 , 96.Xr mac_mls 4 , 97.Xr mac_none 4 , 98.Xr mac_partition 4 , 99.Xr mac_portacl 4 , 100.Xr mac_seeotheruids 4 , 101.Xr mac_test 4 , 102.Xr mac 9 103.Sh BUGS 104While the MAC Framework design is intended to support the containment of 105the root user, not all attack channels are currently protected by entry 106point checks. 107As such, MAC Framework policies should not be relied on, in isolation, 108to protect against a malicious privileged user. 109