name : check_extable.sh #! /bin/bash # SPDX-License-Identifier: GPL-2.0 # (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com> obj=$1 file ${obj} | grep -q ELF || (echo "${obj} is not an 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