[PATCH 4/4] kselftest/arm64: Add tests for POR_EL0 save/reset/restore

[Kevin Brodsky <kevin.brodsky@arm.com>]

POR_EL0 is expected to be:
- Saved in the poe_context record
- Reset to POR_EL0_INIT when invoking the signal handler
- Restored from poe_context when returning from the signal handler

Add a new test, poe_restore, to check that the save/reset/restore
mechanism is working as intended. See commit 2e8a1acea859 ("arm64:
signal: Improve POR_EL0 handling to avoid uaccess failures") for
more details.

This commit did not handle the case where poe_context is missing
correctly. This was recently fixed; add a new test,
poe_missing_poe_context, to check this case.

Note: td->pass is only set to true at the very end, as an unexpected
signal may occur in case of failure (especially in
poe_missing_poe_context if POR_EL0 is restored to an invalid value).
Failures are tracked with a global, failed_check.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 .../testcases/poe_missing_poe_context.c       | 73 +++++++++++++++++++
 .../arm64/signal/testcases/poe_restore.c      | 64 ++++++++++++++++
 2 files changed, 137 insertions(+)
 create mode 100644 tools/testing/selftests/arm64/signal/testcases/poe_missing_poe_context.c
 create mode 100644 tools/testing/selftests/arm64/signal/testcases/poe_restore.c

diff --git a/tools/testing/selftests/arm64/signal/testcases/poe_missing_poe_context.c b/tools/testing/selftests/arm64/signal/testcases/poe_missing_poe_context.c
new file mode 100644
index 000000000000..abab7400d9df
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/poe_missing_poe_context.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Arm Ltd
+ *
+ * Verify that the POR_EL0 register is left untouched on sigreturn if the
+ * POE frame record is missing.
+ */
+
+#include <asm/sigcontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+#define POR_EL0_INIT	0x07ul
+#define POR_EL0_CUSTOM	0x77ul
+
+static bool failed_check;
+
+static bool modify_por_el0(struct tdescr *td)
+{
+	set_por_el0(POR_EL0_CUSTOM);
+
+	return true;
+}
+
+static int signal_remove_poe_context(struct tdescr *td, siginfo_t *si,
+				      ucontext_t *uc)
+{
+	struct _aarch64_ctx *ctx = GET_UC_RESV_HEAD(uc);
+	struct _aarch64_ctx *poe_ctx_head;
+
+	poe_ctx_head = get_header(ctx, POE_MAGIC, sizeof(uc->uc_mcontext),
+				  NULL);
+	if (!poe_ctx_head) {
+		fprintf(stderr, "Missing poe_context record\n");
+		failed_check = true;
+		return 0;
+	}
+
+	/*
+	 * Actually removing the record would require moving down the next
+	 * records. An easier option is to turn it into an ESR record, which is
+	 * ignored by sigreturn().
+	 */
+	poe_ctx_head->magic = ESR_MAGIC;
+
+	return 0;
+}
+
+static void check_por_el0_preserved(struct tdescr *td)
+{
+	uint64_t por_el0 = get_por_el0();
+
+	if (por_el0 == POR_EL0_INIT) {
+		fprintf(stderr, "POR_EL0 preserved\n");
+	} else {
+		fprintf(stderr, "POR_EL0 unexpectedly set to %lx\n", por_el0);
+		failed_check = true;
+	}
+
+	td->pass = !failed_check;
+}
+
+struct tdescr tde = {
+	.name = "POR_EL0 missing poe_context",
+	.descr = "Remove poe_context record and check POR_EL0 is preserved",
+	.feats_required = FEAT_POE,
+	.timeout = 3,
+	.sig_trig = SIGUSR1,
+	.init = modify_por_el0,
+	.run = signal_remove_poe_context,
+	.check_result = check_por_el0_preserved,
+};
diff --git a/tools/testing/selftests/arm64/signal/testcases/poe_restore.c b/tools/testing/selftests/arm64/signal/testcases/poe_restore.c
new file mode 100644
index 000000000000..9f9a61a4214d
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/poe_restore.c
@@ -0,0 +1,64 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Arm Ltd
+ *
+ * Verify that the POR_EL0 register is saved and restored as expected on signal
+ * entry/return.
+ */
+
+#include <asm/sigcontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+#define POR_EL0_INIT	0x07ul
+#define POR_EL0_CUSTOM	0x77ul
+
+static bool failed_check;
+
+static bool modify_por_el0(struct tdescr *td)
+{
+	set_por_el0(POR_EL0_CUSTOM);
+
+	return true;
+}
+
+static int signal_check_por_el0_reset(struct tdescr *td, siginfo_t *si,
+				      ucontext_t *uc)
+{
+	uint64_t signal_por_el0 = get_por_el0();
+
+	if (signal_por_el0 != POR_EL0_INIT) {
+		fprintf(stderr, "POR_EL0 is %lx in signal handler (expected %lx)\n",
+			signal_por_el0, POR_EL0_INIT);
+		failed_check = true;
+	}
+
+	return 0;
+}
+
+static void check_por_el0_restored(struct tdescr *td)
+{
+	uint64_t por_el0 = get_por_el0();
+
+	if (por_el0 == POR_EL0_CUSTOM) {
+		fprintf(stderr, "POR_EL0 restored\n");
+	} else {
+		fprintf(stderr, "POR_EL0 was %lx but is now %lx\n",
+			POR_EL0_CUSTOM, por_el0);
+		failed_check = true;
+	}
+
+	td->pass = !failed_check;
+}
+
+struct tdescr tde = {
+	.name = "POR_EL0 restore",
+	.descr = "Validate that POR_EL0 is saved/restored on signal entry/return",
+	.feats_required = FEAT_POE,
+	.timeout = 3,
+	.sig_trig = SIGUSR1,
+	.init = modify_por_el0,
+	.run = signal_check_por_el0_reset,
+	.check_result = check_por_el0_restored,
+};
-- 
2.51.2