Annotation of wikisrc/pkgsrc/hardening.mdwn, revision 1.7
1.1 khorben 1: [[!meta title="Hardening pkgsrc"]]
2:
3: [pkgsrc](http://www.pkgsrc.org/) supports a number of mechanisms that are meant
4: to improve the security of compiled binaries. They can be individually enabled
5: in `mk.conf`, and consist of:
6:
7: * `PKGSRC_MKPIE`: forces the creation of PIE (Position Independent
8: Executables) when supported on the current platform. This option is necessary
9: to fully leverage ASLR as a mitigation for security vulnerabilities.
10: * `PKGSRC_USE_FORTIFY`: allows substitute wrappers to be used for commonly used
11: functions that do not bounds checking regularly - but could in some cases.
12: * `PKGSRC_USE_RELRO`: this also makes the exploitation of some security
13: vulnerabilities more difficult in some cases.
14: * `PKGSRC_USE_SSP`: enables stack-smashing protection (again, on supported
15: platforms)
16:
1.2 khorben 17: # Caveats
18:
19: ## Problems with `PKGSRC_MKPIE`
20:
21: ### No support for cwrappers
22:
23: As of the time of this article `PKGSRC_MKPIE` is not supported by
24: `pkgtools/cwrappers` (`USE_CWRAPPERS` in `mk.conf`).
25:
26: ### Packages failing to build
27:
28: A number of packages may fail to build with this option enabled. The failures
29: are often related to the absence of the "-fPIC" compilation flag when building
30: libraries or executables (or ideally "-fPIE" in the latter case). This flag is
31: added to the `CFLAGS` already, but requires the package to actually support it.
32:
33: #### How to fix
34:
35: These instructions are meant as a reference only; they likely need to be adapted
36: for many packages individually.
37:
38: For packages using `Makefiles`:
39:
40: MAKE_FLAGS+= CFLAGS=${CFLAGS:Q}
41: MAKE_FLAGS+= LDFLAGS=${LDFLAGS:Q}
42:
43: For packages using `Imakefiles`:
44:
45: MAKE_FLAGS+= CCOPTIONS=${CFLAGS:Q}
46: MAKE_FLAGS+= LOCAL_LDFLAGS=${LDFLAGS:Q}
47:
48: ### Run-time crashes
49:
50: Some programs may fail to run, or crash at random times once built as PIE. Two
51: scenarios are essentially possible:
52:
53: * actual bug in the program crashing, exposed thanks to ASLR/mprotect;
54: * bug in the implementation of ASLR/mprotect in the Operating System.
55:
1.4 khorben 56: ## Problems with `PKGSRC_USE_FORTIFY`
57:
58: ### Packages failing to build
59:
60: This feature makes use of pre-processing directives to look for hardened,
61: alternative implementations of essential library calls. Some programs may fail
62: to build as a result; this usually happens for those trying too hard to be
63: portable, or otherwise abusing definitions in the standard library.
64:
65: This will require a modification to the program, or disabling this feature for
66: part or all of the build.
67:
68: ### Run-time crashes
69:
70: Just like with `PKGSRC_MKPIE` above, this feature may cause some programs to
71: crash, usually indicating an actual bug in the program. The fix will typically
72: involve patching the original program.
73:
1.7 ! khorben 74: ## Problems with `PKGSRC_USE_RELRO`
! 75:
! 76: ### Performance impact
! 77:
! 78: For better protection, full RELRO requires every symbol to be resolved when the
! 79: program starts, rather than lazily at run-time. This will have more impact on
! 80: programs using a lot of symbols, or linked to libraries exposing a lot of
! 81: symbols. Therefore, daemons or programs otherwise running in background are
! 82: affected only when started. Programs loading plug-ins at run-time are affected
! 83: when loading the plug-ins.
! 84:
! 85: The impact is not expected to be noticeable on modern hardware, except in some
! 86: cases for big programs.
! 87:
1.3 khorben 88: ## Problems with `PKGSRC_USE_SSP`
89:
90: ### Packages failing to build
91:
92: The stack-smashing protection provided by this option does not work for some
93: programs. The two most common situations in which this happens are:
94:
95: * the program makes use of the `alloca(3)` library call (memory allocator on the
96: stack)
97: * the program allocates variables on the stack, with the size determined at
98: run-time.
99:
100: Both cases will require a modification to the program, or disabling this feature
101: for part or all of the build.
102:
103: ### Run-time crashes
104:
1.4 khorben 105: Again, this feature may cause some programs to crash, usually indicating an
106: actual bug in the program. Patching the original program is then required.
1.3 khorben 107:
1.5 khorben 108: # Auditing the system
109:
110: The illusion of security is worse than having no security at all. This section
111: lists a number of ways to ensure the security features requested are actually
112: effective.
113:
114: _These instructions were obtained and tested on a system derived from NetBSD 7
115: (amd64). YMMV._
116:
117: ## Checking for PIE
118:
119: The ELF executable type in use changes for binaries built as PIE; without:
120:
121: $ file /path/to/bin/ary
122: /path/to/bin/ary: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for NetBSD 7.0, not stripped
123:
124: as opposed to the following binary, built as PIE:
125:
126: $ file /path/to/pie/bin/ary
127: /path/to/pie/bin/ary: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for NetBSD 7.0, not stripped
128:
129: The latter result is then what is expected.
130:
131: ## Checking for RELRO
132:
133: The following command should list a section called `RELRO`:
134:
135: $ objdump -p /path/to/bin/ary
136:
137: /path/to/bin/ary: file format elf64-x86-64
138:
139: Program Header:
140: [...]
141: RELRO off 0x0000000000000d78 vaddr 0x0000000000600d78 paddr 0x0000000000600d78 align 2**0
1.6 khorben 142:
143: ## Checking for SSP
144:
145: Building objects, binaries and libraries with SSP will affect the presence of
146: additional symbols in the resulting file:
147:
148: $ nm /path/to/bin/ary
149: [...]
150: U __stack_chk_fail
151: 0000000000600ea0 B __stack_chk_guard
152:
153: This is an indicator that the program was indeed built with support for SSP.
154:
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