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lkdtm: Add REPORT_STACK for checking stack offsets
For validating the stack offset behavior, report the offset from a given process's first seen stack address. Add s script to calculate the results to the LKDTM kselftests. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20210401232347.2791257-7-keescook@chromium.org
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@ -134,6 +134,23 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void)
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__lkdtm_CORRUPT_STACK((void *)&data);
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}
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static pid_t stack_pid;
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static unsigned long stack_addr;
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void lkdtm_REPORT_STACK(void)
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{
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volatile uintptr_t magic;
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pid_t pid = task_pid_nr(current);
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if (pid != stack_pid) {
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pr_info("Starting stack offset tracking for pid %d\n", pid);
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stack_pid = pid;
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stack_addr = (uintptr_t)&magic;
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}
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pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic));
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}
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void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
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{
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static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};
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@ -110,6 +110,7 @@ static const struct crashtype crashtypes[] = {
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CRASHTYPE(EXHAUST_STACK),
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CRASHTYPE(CORRUPT_STACK),
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CRASHTYPE(CORRUPT_STACK_STRONG),
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CRASHTYPE(REPORT_STACK),
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CRASHTYPE(CORRUPT_LIST_ADD),
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CRASHTYPE(CORRUPT_LIST_DEL),
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CRASHTYPE(STACK_GUARD_PAGE_LEADING),
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@ -17,6 +17,7 @@ void lkdtm_LOOP(void);
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void lkdtm_EXHAUST_STACK(void);
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void lkdtm_CORRUPT_STACK(void);
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void lkdtm_CORRUPT_STACK_STRONG(void);
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void lkdtm_REPORT_STACK(void);
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void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void);
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void lkdtm_SOFTLOCKUP(void);
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void lkdtm_HARDLOCKUP(void);
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1
tools/testing/selftests/lkdtm/.gitignore
vendored
1
tools/testing/selftests/lkdtm/.gitignore
vendored
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@ -1,2 +1,3 @@
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*.sh
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!run.sh
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!stack-entropy.sh
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@ -5,6 +5,7 @@ include ../lib.mk
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# NOTE: $(OUTPUT) won't get default value if used before lib.mk
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TEST_FILES := tests.txt
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TEST_PROGS := stack-entropy.sh
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TEST_GEN_PROGS = $(patsubst %,$(OUTPUT)/%.sh,$(shell awk '{print $$1}' tests.txt | sed -e 's/\#//'))
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all: $(TEST_GEN_PROGS)
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36
tools/testing/selftests/lkdtm/stack-entropy.sh
Executable file
36
tools/testing/selftests/lkdtm/stack-entropy.sh
Executable file
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@ -0,0 +1,36 @@
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#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0
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#
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# Measure kernel stack entropy by sampling via LKDTM's REPORT_STACK test.
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set -e
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samples="${1:-1000}"
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# 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 $samples); do
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echo "REPORT_STACK" >/sys/kernel/debug/provoke-crash/DIRECT
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if [ -t 1 ]; then
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percent=$(( 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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exit 1
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else
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exit 0
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fi
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