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| -rwxr-xr-x | scripts/check_extable.sh | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/scripts/check_extable.sh b/scripts/check_extable.sh new file mode 100755 index 0000000..0fb6b1c --- /dev/null +++ b/scripts/check_extable.sh @@ -0,0 +1,146 @@ +#! /bin/bash +# (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com> + +obj=$1 + +file ${obj} | grep -q ELF || (echo "${obj} is not and ELF file." 1>&2 ; exit 0) + +# Bail out early if there isn't an __ex_table section in this object file. +objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null +[ $? -ne 0 ] && exit 0 + +white_list=.text,.fixup + +suspicious_relocs=$(objdump -rj __ex_table ${obj} | tail -n +6 | + grep -v $(eval echo -e{${white_list}}) | awk '{print $3}') + +# No suspicious relocs in __ex_table, jobs a good'un +[ -z "${suspicious_relocs}" ] && exit 0 + + +# After this point, something is seriously wrong since we just found out we +# have some relocations in __ex_table which point to sections which aren't +# white listed. If you're adding a new section in the Linux kernel, and +# you're expecting this section to contain code which can fault (i.e. the +# __ex_table relocation to your new section is expected), simply add your +# new section to the white_list variable above. If not, you're probably +# doing something wrong and the rest of this code is just trying to print +# you more information about it. + +function find_section_offset_from_symbol() +{ + eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /') + + # addr2line takes addresses in hexadecimal... + section_offset=$(printf "0x%016x" $(( ${section_offset} + $2 )) ) +} + +function find_symbol_and_offset_from_reloc() +{ + # Extract symbol and offset from the objdump output + eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/') + + # When the relocation points to the begining of a symbol or section, it + # won't print the offset since it is zero. + if [ -z "${symbol_offset}" ]; then + symbol_offset=0x0 + fi +} + +function find_alt_replacement_target() +{ + # The target of the .altinstr_replacement is the relocation just before + # the .altinstr_replacement one. + eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' | + sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/') +} + +function handle_alt_replacement_reloc() +{ + # This will define alt_target_section and alt_target_section_offset + find_alt_replacement_target ${section} ${section_offset} + + echo "Error: found a reference to .altinstr_replacement in __ex_table:" + addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}' + + error=true +} + +function is_executable_section() +{ + objdump -hwj ${section} ${obj} | grep -q CODE + return $? +} + +function handle_suspicious_generic_reloc() +{ + if is_executable_section ${section}; then + # We've got a relocation to a non white listed _executable_ + # section, print a warning so the developper adds the section to + # the white list or fix his code. We try to pretty-print the file + # and line number where that relocation was added. + echo "Warning: found a reference to section \"${section}\" in __ex_table:" + addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}' + else + # Something is definitively wrong here since we've got a relocation + # to a non-executable section, there's no way this would ever be + # running in the kernel. + echo "Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}" + error=true + fi +} + +function handle_suspicious_reloc() +{ + case "${section}" in + ".altinstr_replacement") + handle_alt_replacement_reloc ${section} ${section_offset} + ;; + *) + handle_suspicious_generic_reloc ${section} ${section_offset} + ;; + esac +} + +function diagnose() +{ + + for reloc in ${suspicious_relocs}; do + # Let's find out where the target of the relocation in __ex_table + # is, this will define ${symbol} and ${symbol_offset} + find_symbol_and_offset_from_reloc ${reloc} + + # When there's a global symbol at the place of the relocation, + # objdump will use it instead of giving us a section+offset, so + # let's find out which section is this symbol in and the total + # offset withing that section. + find_section_offset_from_symbol ${symbol} ${symbol_offset} + + # In this case objdump was presenting us with a reloc to a symbol + # rather than a section. Now that we've got the actual section, + # we can skip it if it's in the white_list. + if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then + continue; + fi + + # Will either print a warning if the relocation happens to be in a + # section we do not know but has executable bit set, or error out. + handle_suspicious_reloc + done +} + +function check_debug_info() { + objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null || + echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \ + "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output." +} + +check_debug_info + +diagnose + +if [ "${error}" ]; then + exit 1 +fi + +exit 0 |
