Annotation of wikisrc/pkgsrc/hardening.mdwn, revision 1.12
1.1 khorben 1: [[!meta title="Hardening pkgsrc"]]
2:
1.9 khorben 3: A number of mechanisms are available in [pkgsrc](http://www.pkgsrc.org/) to
4: improve the security of the resulting system. They can be enabled individually
1.1 khorben 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
1.11 khorben 79: program starts, rather than simply when required at run-time. This will have
80: more impact on programs using a lot of symbols, or linked to libraries exposing
81: a lot of symbols. Therefore, daemons or programs otherwise running in
82: background are affected only when started. Programs loading plug-ins at
83: run-time are affected when loading the plug-ins.
1.7 khorben 84:
85: The impact is not expected to be noticeable on modern hardware, except in some
86: cases for big programs.
87:
1.12 ! khorben 88: ### Run-time crashes
! 89:
! 90: Some programs handle plug-ins and dependencies in a way that conflicts with
! 91: RELRO: for instance, with an initialization routine listing any other plug-in
! 92: required. With full RELRO, the missing symbols are resolved before the
! 93: initialization routine can run, and the dynamic loader will not be able to find
! 94: them directly and abort as a result. Unfortunately, this is how Xorg loads its
! 95: drivers. Partial RELRO can be applied instead in this case.
! 96:
1.3 khorben 97: ## Problems with `PKGSRC_USE_SSP`
98:
99: ### Packages failing to build
100:
101: The stack-smashing protection provided by this option does not work for some
102: programs. The two most common situations in which this happens are:
103:
104: * the program makes use of the `alloca(3)` library call (memory allocator on the
105: stack)
106: * the program allocates variables on the stack, with the size determined at
107: run-time.
108:
109: Both cases will require a modification to the program, or disabling this feature
110: for part or all of the build.
111:
112: ### Run-time crashes
113:
1.4 khorben 114: Again, this feature may cause some programs to crash, usually indicating an
115: actual bug in the program. Patching the original program is then required.
1.3 khorben 116:
1.8 khorben 117: ### Performance impact
118:
119: The compiler emits extra code when using this feature: a check for buffer
120: overflows is performed when entering and exiting functions, requiring an extra
121: variable on the stack. The level of protection can otherwise be adjusted to
122: affect only those functions considered more sensitive by the compiler (with
123: `-fstack-protector` instead of `-fstack-protector-all`).
124:
125: The impact is not expected to be noticeable on modern hardware. However,
126: programs with a hard requirement to run at the fastest possible speed should
127: avoid using this feature, or using libraries built with this feature.
128:
1.5 khorben 129: # Auditing the system
130:
131: The illusion of security is worse than having no security at all. This section
132: lists a number of ways to ensure the security features requested are actually
133: effective.
134:
135: _These instructions were obtained and tested on a system derived from NetBSD 7
136: (amd64). YMMV._
137:
138: ## Checking for PIE
139:
140: The ELF executable type in use changes for binaries built as PIE; without:
141:
142: $ file /path/to/bin/ary
143: /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
144:
145: as opposed to the following binary, built as PIE:
146:
147: $ file /path/to/pie/bin/ary
148: /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
149:
150: The latter result is then what is expected.
151:
152: ## Checking for RELRO
153:
154: The following command should list a section called `RELRO`:
155:
156: $ objdump -p /path/to/bin/ary
157:
158: /path/to/bin/ary: file format elf64-x86-64
159:
160: Program Header:
161: [...]
162: RELRO off 0x0000000000000d78 vaddr 0x0000000000600d78 paddr 0x0000000000600d78 align 2**0
1.6 khorben 163:
164: ## Checking for SSP
165:
166: Building objects, binaries and libraries with SSP will affect the presence of
167: additional symbols in the resulting file:
168:
169: $ nm /path/to/bin/ary
170: [...]
171: U __stack_chk_fail
172: 0000000000600ea0 B __stack_chk_guard
173:
174: This is an indicator that the program was indeed built with support for SSP.
175:
1.10 khorben 176: # References
177:
178: * <http://tk-blog.blogspot.co.at/2009/02/relro-not-so-well-known-memory.html>
179:
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