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kernel
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linux
selftests/powerpc: Add test of mitigation patching
We recently discovered some of our mitigation patching was not safe
against other CPUs running concurrently.
Add a test which enable/disables all mitigations in a tight loop while
also running some stress load. On an unpatched system this almost always
leads to an oops and panic/reboot, but we also check if the kernel
becomes tainted in case we have a non-fatal oops.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210507064225.1556312-1-mpe@ellerman.id.au
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tools/testing/selftests/powerpc/security/Makefile
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tools/testing/selftests/powerpc/security/Makefile
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tools/testing/selftests/powerpc/security/mitigation-patching.sh
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tools/testing/selftests/powerpc/security/mitigation-patching.sh
···
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#!/usr/bin/env bash
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set -euo pipefail
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TIMEOUT=10
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function do_one
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{
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local mitigation="$1"
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local orig
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local start
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local now
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orig=$(cat "$mitigation")
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start=$EPOCHSECONDS
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now=$start
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while [[ $((now-start)) -lt "$TIMEOUT" ]]
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do
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echo 0 > "$mitigation"
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echo 1 > "$mitigation"
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now=$EPOCHSECONDS
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done
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echo "$orig" > "$mitigation"
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}
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rc=0
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cd /sys/kernel/debug/powerpc || rc=1
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if [[ "$rc" -ne 0 ]]; then
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echo "Error: couldn't cd to /sys/kernel/debug/powerpc" >&2
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exit 1
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fi
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tainted=$(cat /proc/sys/kernel/tainted)
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if [[ "$tainted" -ne 0 ]]; then
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echo "Error: kernel already tainted!" >&2
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exit 1
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fi
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mitigations="barrier_nospec stf_barrier count_cache_flush rfi_flush entry_flush uaccess_flush"
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for m in $mitigations
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do
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do_one "$m" &
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done
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echo "Spawned threads enabling/disabling mitigations ..."
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if stress-ng > /dev/null 2>&1; then
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stress="stress-ng"
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elif stress > /dev/null 2>&1; then
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stress="stress"
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else
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stress=""
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fi
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if [[ -n "$stress" ]]; then
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"$stress" -m "$(nproc)" -t "$TIMEOUT" &
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echo "Spawned VM stressors ..."
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fi
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echo "Waiting for timeout ..."
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wait
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tainted=$(cat /proc/sys/kernel/tainted)
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if [[ "$tainted" -ne 0 ]]; then
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echo "Error: kernel became tainted!" >&2
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exit 1
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fi
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echo "OK"
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exit 0