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1#! /bin/bash
2# (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com>
3
4obj=$1
5
6file ${obj} | grep -q ELF || (echo "${obj} is not and ELF file." 1>&2 ; exit 0)
7
8# Bail out early if there isn't an __ex_table section in this object file.
9objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null
10[ $? -ne 0 ] && exit 0
11
12white_list=.text,.fixup
13
14suspicious_relocs=$(objdump -rj __ex_table ${obj} | tail -n +6 |
15 grep -v $(eval echo -e{${white_list}}) | awk '{print $3}')
16
17# No suspicious relocs in __ex_table, jobs a good'un
18[ -z "${suspicious_relocs}" ] && exit 0
19
20
21# After this point, something is seriously wrong since we just found out we
22# have some relocations in __ex_table which point to sections which aren't
23# white listed. If you're adding a new section in the Linux kernel, and
24# you're expecting this section to contain code which can fault (i.e. the
25# __ex_table relocation to your new section is expected), simply add your
26# new section to the white_list variable above. If not, you're probably
27# doing something wrong and the rest of this code is just trying to print
28# you more information about it.
29
30function find_section_offset_from_symbol()
31{
32 eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /')
33
34 # addr2line takes addresses in hexadecimal...
35 section_offset=$(printf "0x%016x" $(( ${section_offset} + $2 )) )
36}
37
38function find_symbol_and_offset_from_reloc()
39{
40 # Extract symbol and offset from the objdump output
41 eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/')
42
43 # When the relocation points to the begining of a symbol or section, it
44 # won't print the offset since it is zero.
45 if [ -z "${symbol_offset}" ]; then
46 symbol_offset=0x0
47 fi
48}
49
50function find_alt_replacement_target()
51{
52 # The target of the .altinstr_replacement is the relocation just before
53 # the .altinstr_replacement one.
54 eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' |
55 sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/')
56}
57
58function handle_alt_replacement_reloc()
59{
60 # This will define alt_target_section and alt_target_section_offset
61 find_alt_replacement_target ${section} ${section_offset}
62
63 echo "Error: found a reference to .altinstr_replacement in __ex_table:"
64 addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}'
65
66 error=true
67}
68
69function is_executable_section()
70{
71 objdump -hwj ${section} ${obj} | grep -q CODE
72 return $?
73}
74
75function handle_suspicious_generic_reloc()
76{
77 if is_executable_section ${section}; then
78 # We've got a relocation to a non white listed _executable_
79 # section, print a warning so the developper adds the section to
80 # the white list or fix his code. We try to pretty-print the file
81 # and line number where that relocation was added.
82 echo "Warning: found a reference to section \"${section}\" in __ex_table:"
83 addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}'
84 else
85 # Something is definitively wrong here since we've got a relocation
86 # to a non-executable section, there's no way this would ever be
87 # running in the kernel.
88 echo "Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}"
89 error=true
90 fi
91}
92
93function handle_suspicious_reloc()
94{
95 case "${section}" in
96 ".altinstr_replacement")
97 handle_alt_replacement_reloc ${section} ${section_offset}
98 ;;
99 *)
100 handle_suspicious_generic_reloc ${section} ${section_offset}
101 ;;
102 esac
103}
104
105function diagnose()
106{
107
108 for reloc in ${suspicious_relocs}; do
109 # Let's find out where the target of the relocation in __ex_table
110 # is, this will define ${symbol} and ${symbol_offset}
111 find_symbol_and_offset_from_reloc ${reloc}
112
113 # When there's a global symbol at the place of the relocation,
114 # objdump will use it instead of giving us a section+offset, so
115 # let's find out which section is this symbol in and the total
116 # offset withing that section.
117 find_section_offset_from_symbol ${symbol} ${symbol_offset}
118
119 # In this case objdump was presenting us with a reloc to a symbol
120 # rather than a section. Now that we've got the actual section,
121 # we can skip it if it's in the white_list.
122 if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then
123 continue;
124 fi
125
126 # Will either print a warning if the relocation happens to be in a
127 # section we do not know but has executable bit set, or error out.
128 handle_suspicious_reloc
129 done
130}
131
132function check_debug_info() {
133 objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null ||
134 echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \
135 "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output."
136}
137
138check_debug_info
139
140diagnose
141
142if [ "${error}" ]; then
143 exit 1
144fi
145
146exit 0
1#! /bin/bash
2# SPDX-License-Identifier: GPL-2.0
3# (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com>
4
5obj=$1
6
7file ${obj} | grep -q ELF || (echo "${obj} is not and ELF file." 1>&2 ; exit 0)
8
9# Bail out early if there isn't an __ex_table section in this object file.
10objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null
11[ $? -ne 0 ] && exit 0
12
13white_list=.text,.fixup
14
15suspicious_relocs=$(objdump -rj __ex_table ${obj} | tail -n +6 |
16 grep -v $(eval echo -e{${white_list}}) | awk '{print $3}')
17
18# No suspicious relocs in __ex_table, jobs a good'un
19[ -z "${suspicious_relocs}" ] && exit 0
20
21
22# After this point, something is seriously wrong since we just found out we
23# have some relocations in __ex_table which point to sections which aren't
24# white listed. If you're adding a new section in the Linux kernel, and
25# you're expecting this section to contain code which can fault (i.e. the
26# __ex_table relocation to your new section is expected), simply add your
27# new section to the white_list variable above. If not, you're probably
28# doing something wrong and the rest of this code is just trying to print
29# you more information about it.
30
31function find_section_offset_from_symbol()
32{
33 eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /')
34
35 # addr2line takes addresses in hexadecimal...
36 section_offset=$(printf "0x%016x" $(( ${section_offset} + $2 )) )
37}
38
39function find_symbol_and_offset_from_reloc()
40{
41 # Extract symbol and offset from the objdump output
42 eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/')
43
44 # When the relocation points to the begining of a symbol or section, it
45 # won't print the offset since it is zero.
46 if [ -z "${symbol_offset}" ]; then
47 symbol_offset=0x0
48 fi
49}
50
51function find_alt_replacement_target()
52{
53 # The target of the .altinstr_replacement is the relocation just before
54 # the .altinstr_replacement one.
55 eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' |
56 sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/')
57}
58
59function handle_alt_replacement_reloc()
60{
61 # This will define alt_target_section and alt_target_section_offset
62 find_alt_replacement_target ${section} ${section_offset}
63
64 echo "Error: found a reference to .altinstr_replacement in __ex_table:"
65 addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}'
66
67 error=true
68}
69
70function is_executable_section()
71{
72 objdump -hwj ${section} ${obj} | grep -q CODE
73 return $?
74}
75
76function handle_suspicious_generic_reloc()
77{
78 if is_executable_section ${section}; then
79 # We've got a relocation to a non white listed _executable_
80 # section, print a warning so the developper adds the section to
81 # the white list or fix his code. We try to pretty-print the file
82 # and line number where that relocation was added.
83 echo "Warning: found a reference to section \"${section}\" in __ex_table:"
84 addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}'
85 else
86 # Something is definitively wrong here since we've got a relocation
87 # to a non-executable section, there's no way this would ever be
88 # running in the kernel.
89 echo "Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}"
90 error=true
91 fi
92}
93
94function handle_suspicious_reloc()
95{
96 case "${section}" in
97 ".altinstr_replacement")
98 handle_alt_replacement_reloc ${section} ${section_offset}
99 ;;
100 *)
101 handle_suspicious_generic_reloc ${section} ${section_offset}
102 ;;
103 esac
104}
105
106function diagnose()
107{
108
109 for reloc in ${suspicious_relocs}; do
110 # Let's find out where the target of the relocation in __ex_table
111 # is, this will define ${symbol} and ${symbol_offset}
112 find_symbol_and_offset_from_reloc ${reloc}
113
114 # When there's a global symbol at the place of the relocation,
115 # objdump will use it instead of giving us a section+offset, so
116 # let's find out which section is this symbol in and the total
117 # offset withing that section.
118 find_section_offset_from_symbol ${symbol} ${symbol_offset}
119
120 # In this case objdump was presenting us with a reloc to a symbol
121 # rather than a section. Now that we've got the actual section,
122 # we can skip it if it's in the white_list.
123 if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then
124 continue;
125 fi
126
127 # Will either print a warning if the relocation happens to be in a
128 # section we do not know but has executable bit set, or error out.
129 handle_suspicious_reloc
130 done
131}
132
133function check_debug_info() {
134 objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null ||
135 echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \
136 "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output."
137}
138
139check_debug_info
140
141diagnose
142
143if [ "${error}" ]; then
144 exit 1
145fi
146
147exit 0