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
---
.../selftests/powerpc/security/Makefile | 2 +
.../powerpc/security/mitigation-patching.sh | 75 +++
2 files changed, 77 insertions(+)
create mode 100755
tools/testing/selftests/powerpc/security/mitigation-patching.sh
diff --git a/tools/testing/selftests/powerpc/security/Makefile
b/tools/testing/selftests/powerpc/security/Makefile
index 844d18cd5f93..7488315fd847 100644
--- a/tools/testing/selftests/powerpc/security/Makefile
+++ b/tools/testing/selftests/powerpc/security/Makefile
@@ -1,6 +1,8 @@
# SPDX-License-Identifier: GPL-2.0+
TEST_GEN_PROGS := rfi_flush entry_flush uaccess_flush spectre_v2
+TEST_PROGS := mitigation-patching.sh
+
top_srcdir = ../../../../..
CFLAGS += -I../../../../../usr/include
diff --git a/tools/testing/selftests/powerpc/security/mitigation-patching.sh
b/tools/testing/selftests/powerpc/security/mitigation-patching.sh
new file mode 100755
index ..00197acb7ff1
--- /dev/null
+++ b/tools/testing/selftests/powerpc/security/mitigation-patching.sh
@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+TIMEOUT=10
+
+function do_one
+{
+local mitigation="$1"
+local orig
+local start
+local now
+
+orig=$(cat "$mitigation")
+
+start=$EPOCHSECONDS
+now=$start
+
+while [[ $((now-start)) -lt "$TIMEOUT" ]]
+do
+echo 0 > "$mitigation"
+echo 1 > "$mitigation"
+
+now=$EPOCHSECONDS
+done
+
+echo "$orig" > "$mitigation"
+}
+
+rc=0
+cd /sys/kernel/debug/powerpc || rc=1
+if [[ "$rc" -ne 0 ]]; then
+echo "Error: couldn't cd to /sys/kernel/debug/powerpc" >&2
+exit 1
+fi
+
+tainted=$(cat /proc/sys/kernel/tainted)
+if [[ "$tainted" -ne 0 ]]; then
+echo "Error: kernel already tainted!" >&2
+exit 1
+fi
+
+mitigations="barrier_nospec stf_barrier count_cache_flush rfi_flush
entry_flush uaccess_flush"
+
+for m in $mitigations
+do
+do_one "$m" &
+done
+
+echo "Spawned threads enabling/disabling mitigations ..."
+
+if stress-ng > /dev/null 2>&1; then
+stress="stress-ng"
+elif stress > /dev/null 2>&1; then
+stress="stress"
+else
+stress=""
+fi
+
+if [[ -n "$stress" ]]; then
+"$stress" -m "$(nproc)" -t "$TIMEOUT" &
+echo "Spawned VM stressors ..."
+fi
+
+echo "Waiting for timeout ..."
+wait
+
+tainted=$(cat /proc/sys/kernel/tainted)
+if [[ "$tainted" -ne 0 ]]; then
+echo "Error: kernel became tainted!" >&2
+exit 1
+fi
+
+echo "OK"
+exit 0
--
2.25.1
