kselftest/arm64: Add tests for POR_EL0 save/reset/restore

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>
Signed-off-by: Will Deacon <will@kernel.org>

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 (file)
index 0000000..3f22d8c
--- /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);
+       size_t resv_size = GET_UCP_RESV_SIZE(uc);
+       struct _aarch64_ctx *poe_ctx_head;
+
+       poe_ctx_head = get_header(ctx, POE_MAGIC, resv_size, 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 (file)
index 0000000..9f9a61a
--- /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,
+};