linux/scripts/check_extable.sh at master · multikernel/linux · GitHub

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#! /bin/bash

# SPDX-License-Identifier: GPL-2.0

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

}

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

}

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;

# 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

exit 0

linux/scripts/check_extable.sh at master · multikernel/linux · GitHub

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