tools/testing/selftests/lkdtm/stack-entropy.sh

   1 #!/bin/sh
   2 # SPDX-License-Identifier: GPL-2.0
   3 #
   4 # Measure kernel stack entropy by sampling via LKDTM's REPORT_STACK test.
   5 set -e
   6 samples="${1:-1000}"
   7
   8 # Capture dmesg continuously since it may fill up depending on sample size.
   9 log=$(mktemp -t stack-entropy-XXXXXX)
  10 dmesg --follow >"$log" & pid=$!
  11 report=-1
  12 for i in $(seq 1 $samples); do
  13         echo "REPORT_STACK" >/sys/kernel/debug/provoke-crash/DIRECT
  14         if [ -t 1 ]; then
  15                 percent=$(( 100 * $i / $samples ))
  16                 if [ "$percent" -ne "$report" ]; then
  17                         /bin/echo -en "$percent%\r"
  18                         report="$percent"
  19                 fi
  20         fi
  21 done
  22 kill "$pid"
  23
  24 # Count unique offsets since last run.
  25 seen=$(tac "$log" | grep -m1 -B"$samples"0 'Starting stack offset' | \
  26         grep 'Stack offset' | awk '{print $NF}' | sort | uniq -c | wc -l)
  27 bits=$(echo "obase=2; $seen" | bc | wc -L)
  28 echo "Bits of stack entropy: $bits"
  29 rm -f "$log"
  30
  31 # We would expect any functional stack randomization to be at least 5 bits.
  32 if [ "$bits" -lt 5 ]; then
  33         exit 1
  34 else
  35         exit 0
  36 fi