[PATCH 2/4] selftests/arm: Add signal tests

[Dev Jain]

This patch introduces two signal tests, and generic test wrappers similar to
selftests/arm64/signal directory, along with the mangling testcases found
therein. arm_cpsr, dumped by the kernel to user space in the ucontext structure
to the signal handler, is mangled with. The kernel must spot this illegal
attempt and the testcases are expected to terminate via SEGV.

Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 .../selftests/arm/signal/test_signals.c       |  27 ++
 .../selftests/arm/signal/test_signals.h       |  74 +++++
 .../selftests/arm/signal/test_signals_utils.c | 257 ++++++++++++++++++
 .../selftests/arm/signal/test_signals_utils.h | 128 +++++++++
 .../signal/testcases/mangle_cpsr_aif_bits.c   |  33 +++
 .../mangle_cpsr_invalid_compat_toggle.c       |  29 ++
 6 files changed, 548 insertions(+)
 create mode 100644 tools/testing/selftests/arm/signal/test_signals.c
 create mode 100644 tools/testing/selftests/arm/signal/test_signals.h
 create mode 100644 tools/testing/selftests/arm/signal/test_signals_utils.c
 create mode 100644 tools/testing/selftests/arm/signal/test_signals_utils.h
 create mode 100644 tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
 create mode 100644 tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c

diff --git a/tools/testing/selftests/arm/signal/test_signals.c b/tools/testing/selftests/arm/signal/test_signals.c
new file mode 100644
index 000000000000..1ecf1e9f041c
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/test_signals.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 ARM Limited
+ *
+ * Generic test wrapper for arm signal tests.
+ *
+ * Each test provides its own tde struct tdescr descriptor to link with
+ * this wrapper. Framework provides common helpers.
+ */
+#include <kselftest.h>
+
+#include "test_signals.h"
+#include "test_signals_utils.h"
+
+struct tdescr *current = &tde;
+
+int main(int argc, char *argv[])
+{
+	ksft_print_msg("%s :: %s\n", current->name, current->descr);
+	if (test_setup(current) && test_init(current)) {
+		test_run(current);
+		test_cleanup(current);
+	}
+	test_result(current);
+
+	return current->result;
+}
diff --git a/tools/testing/selftests/arm/signal/test_signals.h b/tools/testing/selftests/arm/signal/test_signals.h
new file mode 100644
index 000000000000..bbd147127d66
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/test_signals.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2024 ARM Limited */
+
+#ifndef __TEST_SIGNALS_H__
+#define __TEST_SIGNALS_H__
+
+#include <signal.h>
+#include <stdbool.h>
+#include <ucontext.h>
+
+/*
+ * Using ARCH specific and sanitized Kernel headers from the tree.
+ */
+#include <asm/ptrace.h>
+#include <asm/hwcap.h>
+
+/*
+ * A descriptor used to describe and configure a test case.
+ * Fields with a non-trivial meaning are described inline in the following.
+ */
+struct tdescr {
+	/* KEEP THIS FIELD FIRST for easier lookup from assembly */
+	void			*token;
+	/* when disabled token based sanity checking is skipped in handler */
+	bool			sanity_disabled;
+	/* just a name for the test-case; manadatory field */
+	char			*name;
+	char			*descr;
+
+	bool			initialized;
+	unsigned int		minsigstksz;
+	/* signum used as a test trigger. Zero if no trigger-signal is used */
+	int			sig_trig;
+	/*
+	 * signum considered as a successful test completion.
+	 * Zero when no signal is expected on success
+	 */
+	int			sig_ok;
+	/* signum expected on unsupported CPU features. */
+	int			sig_unsupp;
+	/* a timeout in second for test completion */
+	unsigned int		timeout;
+	bool			triggered;
+	bool			pass;
+	unsigned int		result;
+	/* optional sa_flags for the installed handler */
+	int			sa_flags;
+	ucontext_t		saved_uc;
+	/* used by get_current_ctx() */
+	size_t			live_sz;
+	ucontext_t		*live_uc;
+	volatile sig_atomic_t	live_uc_valid;
+	/* optional test private data */
+	void			*priv;
+
+	/* a custom setup: called alternatively to default_setup */
+	int (*setup)(struct tdescr *td);
+	/* a custom init: called by default test init after test_setup */
+	bool (*init)(struct tdescr *td);
+	/* a custom cleanup function called before test exits */
+	void (*cleanup)(struct tdescr *td);
+	/* an optional function to be used as a trigger for starting test */
+	int (*trigger)(struct tdescr *td);
+	/*
+	 * the actual test-core: invoked differently depending on the
+	 * presence of the trigger function above; this is mandatory
+	 */
+	int (*run)(struct tdescr *td, siginfo_t *si, ucontext_t *uc);
+	/* an optional function for custom results' processing */
+	void (*check_result)(struct tdescr *td);
+};
+
+extern struct tdescr tde;
+#endif
diff --git a/tools/testing/selftests/arm/signal/test_signals_utils.c b/tools/testing/selftests/arm/signal/test_signals_utils.c
new file mode 100644
index 000000000000..96aeb11de151
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/test_signals_utils.c
@@ -0,0 +1,257 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2024 ARM Limited */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+#include <assert.h>
+#include <sys/auxv.h>
+#include <linux/auxvec.h>
+#include <ucontext.h>
+
+#include <asm/unistd.h>
+
+#include <kselftest.h>
+
+#include "test_signals.h"
+#include "test_signals_utils.h"
+
+
+extern struct tdescr *current;
+
+static int sig_copyctx = SIGTRAP;
+
+static void unblock_signal(int signum)
+{
+	sigset_t sset;
+
+	sigemptyset(&sset);
+	sigaddset(&sset, signum);
+	sigprocmask(SIG_UNBLOCK, &sset, NULL);
+}
+
+static void default_result(struct tdescr *td, bool force_exit)
+{
+	if (td->result == KSFT_SKIP) {
+		fprintf(stderr, "==>> completed. SKIP.\n");
+	} else if (td->pass) {
+		fprintf(stderr, "==>> completed. PASS(1)\n");
+		td->result = KSFT_PASS;
+	} else {
+		fprintf(stdout, "==>> completed. FAIL(0)\n");
+		td->result = KSFT_FAIL;
+	}
+
+	if (force_exit)
+		exit(td->result);
+}
+
+/*
+ * The following handle_signal_* helpers are used by main default_handler
+ * and are meant to return true when signal is handled successfully:
+ * when false is returned instead, it means that the signal was somehow
+ * unexpected in that context and it was NOT handled; default_handler will
+ * take care of such unexpected situations.
+ */
+
+static bool handle_signal_unsupported(struct tdescr *td,
+				      siginfo_t *si, void *uc)
+{
+
+	/* Mangling PC to avoid loops on original SIGILL */
+	((ucontext_t *)uc)->uc_mcontext.arm_pc += 4;
+
+	if (!td->initialized) {
+		fprintf(stderr,
+			"Got SIG_UNSUPP @test_init. Ignore.\n");
+	} else {
+		fprintf(stderr,
+			"-- RX SIG_UNSUPP on unsupported feat...OK\n");
+		td->pass = 1;
+		default_result(current, 1);
+	}
+
+	return true;
+}
+
+static bool handle_signal_trigger(struct tdescr *td,
+				  siginfo_t *si, void *uc)
+{
+	td->triggered = 1;
+
+	/* ->run was asserted NON-NULL in test_setup() already */
+	td->run(td, si, uc);
+
+	return true;
+}
+
+static bool handle_signal_ok(struct tdescr *td,
+			     siginfo_t *si, void *uc)
+{
+
+	/*
+	 * it's a bug in the test code when this assert fail:
+	 * if sig_trig was defined, it must have been used before getting here.
+	 */
+	assert(!td->sig_trig || td->triggered);
+	fprintf(stderr,
+		"SIG_OK -- SP:0x%lX  si_addr@:%p  si_code:%d  token@:%p  offset:%d\n",
+		((ucontext_t *)uc)->uc_mcontext.arm_sp,
+		si->si_addr, si->si_code, td->token, td->token - si->si_addr);
+
+	/*
+	 * Trying to narrow down the SEGV to the ones generated by Kernel itself
+	 * via arm64_notify_segfault(). This is a best-effort check anyway, and
+	 * the si_code check may need to change if this aspect of the kernel
+	 * ABI changes.
+	 */
+	if (td->sig_ok == SIGSEGV && si->si_code != SEGV_ACCERR) {
+		fprintf(stdout,
+			"si_code != SEGV_ACCERR...test is probably broken!\n");
+		abort();
+	}
+	td->pass = 1;
+	/*
+	 * Some tests can lead to SEGV loops: in such a case we want to
+	 * terminate immediately exiting straight away; some others are not
+	 * supposed to outlive the signal handler code, due to the content of
+	 * the fake sigframe which caused the signal itself.
+	 */
+	default_result(current, 1);
+
+	return true;
+}
+
+static void default_handler(int signum, siginfo_t *si, void *uc)
+{
+	if (current->sig_unsupp && signum == current->sig_unsupp &&
+	    handle_signal_unsupported(current, si, uc)) {
+		fprintf(stderr, "Handled SIG_UNSUPP\n");
+	} else if (current->sig_trig && signum == current->sig_trig &&
+		   handle_signal_trigger(current, si, uc)) {
+		fprintf(stderr, "Handled SIG_TRIG\n");
+	} else if (current->sig_ok && signum == current->sig_ok &&
+		   handle_signal_ok(current, si, uc)) {
+		fprintf(stderr, "Handled SIG_OK\n");
+	} else if (signum == sig_copyctx && current->live_uc) {
+		fprintf(stderr, "Handled SIG_COPYCTX\n");
+	} else {
+		if (signum == SIGALRM && current->timeout) {
+			fprintf(stderr, "-- Timeout !\n");
+		} else {
+			fprintf(stderr,
+				"-- RX UNEXPECTED SIGNAL: %d code %d address %p\n",
+				signum, si->si_code, si->si_addr);
+		}
+		default_result(current, 1);
+	}
+}
+
+static int default_setup(struct tdescr *td)
+{
+	struct sigaction sa;
+
+	sa.sa_sigaction = default_handler;
+	sa.sa_flags = SA_SIGINFO | SA_RESTART;
+	sa.sa_flags |= td->sa_flags;
+	sigemptyset(&sa.sa_mask);
+	/* uncatchable signals naturally skipped ... */
+	for (int sig = 1; sig < 32; sig++)
+		sigaction(sig, &sa, NULL);
+	/*
+	 * RT Signals default disposition is Term but they cannot be
+	 * generated by the Kernel in response to our tests; so just catch
+	 * them all and report them as UNEXPECTED signals.
+	 */
+	for (int sig = SIGRTMIN; sig <= SIGRTMAX; sig++)
+		sigaction(sig, &sa, NULL);
+
+	/* just in case...unblock explicitly all we need */
+	if (td->sig_trig)
+		unblock_signal(td->sig_trig);
+	if (td->sig_ok)
+		unblock_signal(td->sig_ok);
+	if (td->sig_unsupp)
+		unblock_signal(td->sig_unsupp);
+
+	if (td->timeout) {
+		unblock_signal(SIGALRM);
+		alarm(td->timeout);
+	}
+	fprintf(stderr, "Registered handlers for all signals.\n");
+
+	return 1;
+}
+
+static inline int default_trigger(struct tdescr *td)
+{
+	return !raise(td->sig_trig);
+}
+
+int test_init(struct tdescr *td)
+{
+	if (td->sig_trig == sig_copyctx) {
+		fprintf(stdout,
+			"Signal %d is RESERVED, cannot be used as a trigger. Aborting\n",
+			sig_copyctx);
+		return 0;
+	}
+	/* just in case */
+	unblock_signal(sig_copyctx);
+
+	td->minsigstksz = getauxval(AT_MINSIGSTKSZ);
+	if (!td->minsigstksz)
+		td->minsigstksz = MINSIGSTKSZ;
+	fprintf(stderr, "Detected MINSTKSIGSZ:%d\n", td->minsigstksz);
+
+	/* Perform test specific additional initialization */
+	if (td->init && !td->init(td)) {
+		fprintf(stderr, "FAILED Testcase initialization.\n");
+		return 0;
+	}
+	td->initialized = 1;
+	fprintf(stderr, "Testcase initialized.\n");
+
+	return 1;
+}
+
+int test_setup(struct tdescr *td)
+{
+	/* assert core invariants symptom of a rotten testcase */
+	assert(current);
+	assert(td);
+	assert(td->name);
+	assert(td->run);
+
+	/* Default result is FAIL if test setup fails */
+	td->result = KSFT_FAIL;
+	if (td->setup)
+		return td->setup(td);
+	else
+		return default_setup(td);
+}
+
+int test_run(struct tdescr *td)
+{
+	if (td->trigger)
+		return td->trigger(td);
+	else if (td->sig_trig)
+		return default_trigger(td);
+	else
+		return td->run(td, NULL, NULL);
+}
+
+void test_result(struct tdescr *td)
+{
+	if (td->initialized && td->result != KSFT_SKIP && td->check_result)
+		td->check_result(td);
+	default_result(td, 0);
+}
+
+void test_cleanup(struct tdescr *td)
+{
+	if (td->cleanup)
+		td->cleanup(td);
+}
diff --git a/tools/testing/selftests/arm/signal/test_signals_utils.h b/tools/testing/selftests/arm/signal/test_signals_utils.h
new file mode 100644
index 000000000000..386dcc6c268d
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/test_signals_utils.h
@@ -0,0 +1,128 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2024 ARM Limited */
+
+#ifndef __TEST_SIGNALS_UTILS_H__
+#define __TEST_SIGNALS_UTILS_H__
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <linux/compiler.h>
+#include "test_signals.h"
+
+int test_init(struct tdescr *td);
+int test_setup(struct tdescr *td);
+void test_cleanup(struct tdescr *td);
+int test_run(struct tdescr *td);
+void test_result(struct tdescr *td);
+
+/*
+ * Obtaining a valid and full-blown ucontext_t from userspace is tricky:
+ * libc getcontext does() not save all the regs and messes with some of
+ * them (pstate value in particular is not reliable).
+ *
+ * Here we use a service signal to grab the ucontext_t from inside a
+ * dedicated signal handler, since there, it is populated by Kernel
+ * itself in setup_sigframe(). The grabbed context is then stored and
+ * made available in td->live_uc.
+ *
+ * As service-signal is used a SIGTRAP induced by a 'brk' instruction,
+ * because here we have to avoid syscalls to trigger the signal since
+ * they would cause any SVE sigframe content (if any) to be removed.
+ *
+ * Anyway this function really serves a dual purpose:
+ *
+ * 1. grab a valid sigcontext into td->live_uc for result analysis: in
+ * such case it returns 1.
+ *
+ * 2. detect if, somehow, a previously grabbed live_uc context has been
+ * used actively with a sigreturn: in such a case the execution would have
+ * magically resumed in the middle of this function itself (seen_already==1):
+ * in such a case return 0, since in fact we have not just simply grabbed
+ * the context.
+ *
+ * This latter case is useful to detect when a fake_sigreturn test-case has
+ * unexpectedly survived without hitting a SEGV.
+ *
+ * Note that the case of runtime dynamically sized sigframes (like in SVE
+ * context) is still NOT addressed: sigframe size is supposed to be fixed
+ * at sizeof(ucontext_t).
+ */
+static __always_inline bool get_current_context(struct tdescr *td,
+						ucontext_t *dest_uc,
+						size_t dest_sz)
+{
+	static volatile bool seen_already;
+	int i;
+	char *uc = (char *)dest_uc;
+
+	assert(td && dest_uc);
+	/* it's a genuine invocation..reinit */
+	seen_already = 0;
+	td->live_uc_valid = 0;
+	td->live_sz = dest_sz;
+
+	/*
+	 * This is a memset() but we don't want the compiler to
+	 * optimise it into either instructions or a library call
+	 * which might be incompatible with streaming mode.
+	 */
+	for (i = 0; i < td->live_sz; i++) {
+		uc[i] = 0;
+		OPTIMIZER_HIDE_VAR(uc[0]);
+	}
+
+	td->live_uc = dest_uc;
+	/*
+	 * Grab ucontext_t triggering a SIGTRAP.
+	 *
+	 * Note that:
+	 * - live_uc_valid is declared volatile sig_atomic_t in
+	 *   struct tdescr since it will be changed inside the
+	 *   sig_copyctx handler
+	 * - the additional 'memory' clobber is there to avoid possible
+	 *   compiler's assumption on live_uc_valid and the content
+	 *   pointed by dest_uc, which are all changed inside the signal
+	 *   handler
+	 * - BRK causes a debug exception which is handled by the Kernel
+	 *   and finally causes the SIGTRAP signal to be delivered to this
+	 *   test thread. Since such delivery happens on the ret_to_user()
+	 *   /do_notify_resume() debug exception return-path, we are sure
+	 *   that the registered SIGTRAP handler has been run to completion
+	 *   before the execution path is restored here: as a consequence
+	 *   we can be sure that the volatile sig_atomic_t live_uc_valid
+	 *   carries a meaningful result. Being in a single thread context
+	 *   we'll also be sure that any access to memory modified by the
+	 *   handler (namely ucontext_t) will be visible once returned.
+	 * - note that since we are using a breakpoint instruction here
+	 *   to cause a SIGTRAP, the ucontext_t grabbed from the signal
+	 *   handler would naturally contain a PC pointing exactly to this
+	 *   BRK line, which means that, on return from the signal handler,
+	 *   or if we place the ucontext_t on the stack to fake a sigreturn,
+	 *   we'll end up in an infinite loop of BRK-SIGTRAP-handler.
+	 *   For this reason we take care to artificially move forward the
+	 *   PC to the next instruction while inside the signal handler.
+	 */
+	asm volatile ("brk #666"
+		      : "+m" (*dest_uc)
+		      :
+		      : "memory");
+
+	/*
+	 * If we get here with seen_already==1 it implies the td->live_uc
+	 * context has been used to get back here....this probably means
+	 * a test has failed to cause a SEGV...anyway live_uc does not
+	 * point to a just acquired copy of ucontext_t...so return 0
+	 */
+	if (seen_already) {
+		fprintf(stdout,
+			"Unexpected successful sigreturn detected: live_uc is stale !\n");
+		return 0;
+	}
+	seen_already = 1;
+
+	return td->live_uc_valid;
+}
+
+#endif
diff --git a/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
new file mode 100644
index 000000000000..f422cd11ccf2
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 ARM Limited
+ *
+ * Try to mangle the ucontext from inside a signal handler, mangling the
+ * AIF bits in an illegal manner: this attempt must be spotted by Kernel
+ * and the test case is expected to be terminated via SEGV.
+ *
+ */
+
+#include "test_signals_utils.h"
+
+static int mangle_invalid_cpsr_run(struct tdescr *td, siginfo_t *si,
+				   ucontext_t *uc)
+{
+
+	/*
+	 * This config should trigger a SIGSEGV by Kernel when it checks
+	 * the sigframe consistency in valid_user_regs() routine.
+	 */
+	uc->uc_mcontext.arm_cpsr |= PSR_A_BIT | PSR_I_BIT | PSR_F_BIT;
+
+	return 1;
+}
+
+struct tdescr tde = {
+		.sanity_disabled = true,
+		.name = "MANGLE_CPSR_INVALID_AIF_BITS",
+		.descr = "Mangling uc_mcontext with INVALID AIF_BITS",
+		.sig_trig = SIGUSR1,
+		.sig_ok = SIGSEGV,
+		.run = mangle_invalid_cpsr_run,
+};
diff --git a/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c
new file mode 100644
index 000000000000..cb7eb8aec7f2
--- /dev/null
+++ b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2024 ARM Limited
+ *
+ * Try to mangle the ucontext from inside a signal handler, toggling
+ * the execution state bit: this attempt must be spotted by Kernel and
+ * the test case is expected to be terminated via SEGV.
+ */
+
+#include "test_signals_utils.h"
+
+static int mangle_invalid_cpsr_run(struct tdescr *td, siginfo_t *si,
+				   ucontext_t *uc)
+{
+
+	/* This config should trigger a SIGSEGV by Kernel */
+	uc->uc_mcontext.arm_cpsr ^= MODE32_BIT;
+
+	return 1;
+}
+
+struct tdescr tde = {
+		.sanity_disabled = true,
+		.name = "MANGLE_CPSR_INVALID_STATE_TOGGLE",
+		.descr = "Mangling uc_mcontext with INVALID STATE_TOGGLE",
+		.sig_trig = SIGUSR1,
+		.sig_ok = SIGSEGV,
+		.run = mangle_invalid_cpsr_run,
+};
-- 
2.39.2