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https://github.com/xigh/x-trace

FreeBSD 11+12 kernel hacking example : x-trace, simple tool to trace execution
https://github.com/xigh/x-trace

driver freebsd kernel syscalls trace trace-execution

Last synced: 26 days ago
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FreeBSD 11+12 kernel hacking example : x-trace, simple tool to trace execution

Host: GitHub
URL: https://github.com/xigh/x-trace
Owner: xigh
Created: 2016-09-18T18:12:04.000Z (over 8 years ago)
Default Branch: master
Last Pushed: 2019-01-17T14:00:37.000Z (about 6 years ago)
Last Synced: 2024-11-10T19:27:04.697Z (3 months ago)
Topics: driver, freebsd, kernel, syscalls, trace, trace-execution
Language: C
Homepage:
Size: 172 KB
Stars: 1
Watchers: 2
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md

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README

# x-trace
FreeBSD 11+12 kernel hacking example : x-trace, simple tool to trace execution

Description
--------------

This is a simple example of FreeBSD 11 kernel hacking. It comes with a driver (sys/), a userland program that communicates with the driver (bin/xtrace) and two tools (bin/xdump, bin/xdot) to dump the content of the binary file created by xtrace.

How to install
--------------

# git clone https://github.com/xigh/x-trace
# cd x-trace
# make

How to use it
--------------

Load the kernel module:

# kldload sys/xtrace.ko

Trace the execution of /bin/ls:

# bin/xtrace/xtrace /bin/ls
started pid 4467
Makefile bin sys xtrace.out
child returned with 0

Dump the file generated by xtrace:

# bin/xdump/xdump xtrace.out
4466: fork pid=4467
4467: exec '/bin/ls' argc=1 envc=24
argv:
0: /bin/ls
envv:
0: e
1: bin/xtSHELL=/bin/csh
2: SSH_CLIENT=2a01:....
3: LOGNAME=xigh
4: PAGER=more
5: MAIL=/var/mail/xigh
6: PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:...
7: EDITOR=vi
8: ENV=/home/xigh/.shrc
9: OLDPWD=/usr/home/xigh/src
10: PWD=/usr/home/xigh/src/xtrace
11: TERM=xterm-256color
12: SSH_TTY=/dev/pts/1
13: HOME=/root
14: USER=xigh
15: SSH_CONNECTION=2a01:....
16: BLOCKSIZE=K
17: HOSTTYPE=FreeBSD
18: VENDOR=amd
19: OSTYPE=FreeBSD
20: MACHTYPE=x86_64
21: SHLVL=1
22: GROUP=wheel
23: HOST=fbsd11
4467: exit rval=0

Or use the new xexec tool I created:

# bin/xexec/xexec xtrace.out
?:/bin/sh
?:/usr/bin/make
/usr/home/xigh/src/x-trace:/bin/sh "-c" "cc --version || echo 0.0.0"
/usr/home/xigh/src/x-trace:/usr/bin/cc "--version"
/usr/home/xigh/src/x-trace:/bin/sh "-c" "echo \"6.0.1 6.0.1)\" | awk -F. '{print $1 * 10000 + $2 * 100 + $3;}'"
/usr/home/xigh/src/x-trace:/usr/bin/awk "-F." "{print $1 * 10000 + $2 * 100 + $3;}"
/usr/home/xigh/src/x-trace:/bin/sh "-c" "{ echo \"__FreeBSD_cc_version\" | cc -E - 2>/dev/null || echo __FreeBSD_cc_version; } | sed -n '$p'"
/usr/home/xigh/src/x-trace:/usr/bin/sed "-n" "$p"
/usr/home/xigh/src/x-trace:/usr/bin/cc "-E" "-"
/usr/home/xigh/src/x-trace:/usr/bin/cc "-cc1" "-triple" "x86_64-unknown-freebsd12.0" "-E" "-disable-free" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "-" "-mrelocation-model" "static" "-mthread-model" "posix" "-mdisable-fp-elim" "-masm-verbose" "-mconstructor-aliases" "-munwind-tables" "-fuse-init-array" "-target-cpu" "x86-64" "-dwarf-column-info" "-debugger-tuning=gdb" "-resource-dir" "/usr/lib/clang/6.0.1" "-fdebug-compilation-dir" "/usr/home/xigh/src/x-trace" "-ferror-limit" "19" "-fmessage-length" "0" "-fobjc-runtime=gnustep" "-fdiagnostics-show-option" "-o" "-" "-x" "c" "-"
/usr/home/xigh/src/x-trace:/bin/sh "-c" "(ld --version || echo none) | sed -n 1p"
/usr/home/xigh/src/x-trace:/usr/bin/ld "--version"
...

Create a graphviz representation of the trace:

# bin/xdot/xdot xtrace.out
digraph G {
"0:/usr/bin/make\n0:/usr/bin/make\n" -> "1:/bin/sh\n0:sh\n1:-c\n2:cc --version || echo 0...\n"
"1:/bin/sh\n0:sh\n1:-c\n2:cc --version || echo 0...\n" -> "2:/usr/bin/cc\n0:cc\n1:--version\n"
"0:/usr/bin/make\n0:/usr/bin/make\n" -> "3:/bin/sh\n0:sh\n1:-c\n2:echo '3.8.0 3.8.0)' | ...\n"
"3:/bin/sh\n0:sh\n1:-c\n2:echo '3.8.0 3.8.0)' | ...\n" -> "5:/usr/bin/awk\n0:awk\n1:-F.\n2:{print $1 * 10000 + $2...\n"
"0:/usr/bin/make\n0:/usr/bin/make\n" -> "6:/bin/sh\n0:sh\n1:-c\n2:{ echo '__FreeBSD_cc_v...\n"
"6:/bin/sh\n0:sh\n1:-c\n2:{ echo '__FreeBSD_cc_v...\n" -> "8:/usr/bin/sed\n0:sed\n1:-n\n2:$p\n"
"10:/usr/bin/cc\n0:cc\n1:-E\n2:-\n" -> "11:/usr/bin/cc\n0:/usr/bin/cc\n1:-cc1\n2:-triple\n3:x86_64-unknown-freebsd...\n4:-E\n5:-disable-free\n6:-disable-llvm-verifier\n7:-main-file-name\n8:-\n9:-mrelocation-model\n10:static\n11:-mthread-model\n12:posix\n13:-mdisable-fp-elim\n14:-masm-verbose\n15:-mconstructor-aliases\n16:-munwind-tables\n17:-target-cpu\n18:x86-64\n19:-dwarf-column-info\n20:-debugger-tuning=gdb\n21:-resource-dir\n22:/usr/bin/../lib/clang/...\n23:-fdebug-compilation-dir\n24:/usr/home/xigh/src/xtrace\n25:-ferror-limit\n26:19\n27:-fmessage-length\n28:0\n29:-fobjc-runtime=gnustep\n30:-fdiagnostics-show-option\n31:-o\n32:-\n33:-x\n34:c\n35:-\n"
"0:/usr/bin/make\n0:/usr/bin/make\n" -> "12:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n"
"12:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n" -> "13:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=sys/\n"
"13:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=sys/\n" -> "14:/bin/sh\n0:sh\n1:-c\n2:find /usr/src/sys/ -na...\n"
"13:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=sys/\n" -> "14:/usr/bin/find\n0:find\n1:/usr/src/sys/\n2:-name\n3:*_if.m\n"
"13:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=sys/\n" -> "15:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:echo 'Warning: Object ...\n"
"12:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n" -> "16:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/\n"
"16:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/\n" -> "17:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n"
"17:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n" -> "18:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xtrace/\n"
"18:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xtrace/\n" -> "19:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:echo 'Warning: Object ...\n"
"17:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n" -> "20:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xdump/\n"
"20:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xdump/\n" -> "21:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:echo 'Warning: Object ...\n"
"17:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:target=all; for dir i...\n" -> "22:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xdot/\n"
"22:/usr/bin/make\n0:/usr/bin/make\n1:all\n2:DIRPRFX=bin/xdot/\n" -> "23:/bin/sh\n0:/bin/sh\n1:-e\n2:-c\n3:echo 'Warning: Object ...\n"
}

![My image](img/example.png)

How it works
--------------

When the kernel module loads, it install hooks on a few syscalls:

cb_fork = sysent[SYS_fork].sy_call;
sysent[SYS_fork].sy_call = &xtrace_fork;
cb_vfork = sysent[SYS_vfork].sy_call;
sysent[SYS_vfork].sy_call = &xtrace_vfork;
cb_exit = sysent[SYS_exit].sy_call;
sysent[SYS_exit].sy_call = &xtrace_exit;
cb_exec = sysent[SYS_execve].sy_call;
sysent[SYS_execve].sy_call = &xtrace_exec;
cb_chdir = sysent[SYS_chdir].sy_call;
sysent[SYS_chdir].sy_call = &xtrace_chdir;

Then call the original syscall:

static sy_call_t *cb_exit = 0;
static int xtrace_exit(struct thread *td, void *uap) {
return cb_exit(td, uap);
}

Licence
--------------

Copyright (c) 2013-2019 Philippe Anel. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
4. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.