52 lines
1.4 KiB
Bash
52 lines
1.4 KiB
Bash
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#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0
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#
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# Measure kernel stack entropy by sampling via LKDTM's REPORT_STACK test.
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set -e
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samples="${1:-1000}"
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TRIGGER=/sys/kernel/debug/provoke-crash/DIRECT
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KSELFTEST_SKIP_TEST=4
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# Verify we have LKDTM available in the kernel.
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if [ ! -r $TRIGGER ] ; then
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/sbin/modprobe -q lkdtm || true
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if [ ! -r $TRIGGER ] ; then
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echo "Cannot find $TRIGGER (missing CONFIG_LKDTM?)"
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else
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echo "Cannot write $TRIGGER (need to run as root?)"
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fi
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# Skip this test
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exit $KSELFTEST_SKIP_TEST
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fi
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# Capture dmesg continuously since it may fill up depending on sample size.
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log=$(mktemp -t stack-entropy-XXXXXX)
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dmesg --follow >"$log" & pid=$!
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report=-1
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for i in $(seq 1 $samples); do
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echo "REPORT_STACK" > $TRIGGER
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if [ -t 1 ]; then
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percent=$(( 100 * $i / $samples ))
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if [ "$percent" -ne "$report" ]; then
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/bin/echo -en "$percent%\r"
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report="$percent"
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fi
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fi
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done
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kill "$pid"
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# Count unique offsets since last run.
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seen=$(tac "$log" | grep -m1 -B"$samples"0 'Starting stack offset' | \
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grep 'Stack offset' | awk '{print $NF}' | sort | uniq -c | wc -l)
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bits=$(echo "obase=2; $seen" | bc | wc -L)
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echo "Bits of stack entropy: $bits"
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rm -f "$log"
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# We would expect any functional stack randomization to be at least 5 bits.
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if [ "$bits" -lt 5 ]; then
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echo "Stack entropy is low! Booted without 'randomize_kstack_offset=y'?"
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exit 1
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else
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exit 0
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fi
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