kselftest: arm64: mangle_pstate_invalid_compat_toggle and common utils

Add some arm64/signal specific boilerplate and utility code to help
further testcases' development.

Introduce also one simple testcase mangle_pstate_invalid_compat_toggle
and some related helpers: it is a simple mangle testcase which messes
with the ucontext_t from within the signal handler, trying to toggle
PSTATE state bits to switch the system between 32bit/64bit execution
state. Expects SIGSEGV on test PASS.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/Makefile

@@ -4,7 +4,7 @@
 ARCH ?= $(shell uname -m 2>/dev/null || echo not)
 
 ifneq (,$(filter $(ARCH),aarch64 arm64))
-ARM64_SUBTARGETS ?= tags
+ARM64_SUBTARGETS ?= tags signal
 else
 ARM64_SUBTARGETS :=
 endif

tools/testing/selftests/arm64/signal/.gitignore

@@ -0,0 +1,3 @@
+mangle_*
+fake_sigreturn_*
+!*.[ch]

tools/testing/selftests/arm64/signal/Makefile

@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (C) 2019 ARM Limited
+
+# Additional include paths needed by kselftest.h and local headers
+CFLAGS += -D_GNU_SOURCE -std=gnu99 -I.
+
+SRCS := $(filter-out testcases/testcases.c,$(wildcard testcases/*.c))
+PROGS := $(patsubst %.c,%,$(SRCS))
+
+# Generated binaries to be installed by top KSFT script
+TEST_GEN_PROGS := $(notdir $(PROGS))
+
+# Get Kernel headers installed and use them.
+KSFT_KHDR_INSTALL := 1
+
+# Including KSFT lib.mk here will also mangle the TEST_GEN_PROGS list
+# to account for any OUTPUT target-dirs optionally provided by
+# the toplevel makefile
+include ../../lib.mk
+
+$(TEST_GEN_PROGS): $(PROGS)
+	cp $(PROGS) $(OUTPUT)/
+
+clean:
+	$(CLEAN)
+	rm -f $(PROGS)
+
+# Common test-unit targets to build common-layout test-cases executables
+# Needs secondary expansion to properly include the testcase c-file in pre-reqs
+.SECONDEXPANSION:
+$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h
+	$(CC) $(CFLAGS) $^ -o $@

tools/testing/selftests/arm64/signal/README

@@ -0,0 +1,59 @@
+KSelfTest arm64/signal/
+=======================
+
+Signals Tests
++++++++++++++
+
+- Tests are built around a common main compilation unit: such shared main
+  enforces a standard sequence of operations needed to perform a single
+  signal-test (setup/trigger/run/result/cleanup)
+
+- The above mentioned ops are configurable on a test-by-test basis: each test
+  is described (and configured) using the descriptor signals.h::struct tdescr
+
+- Each signal testcase is compiled into its own executable: a separate
+  executable is used for each test since many tests complete successfully
+  by receiving some kind of fatal signal from the Kernel, so it's safer
+  to run each test unit in its own standalone process, so as to start each
+  test from a clean slate.
+
+- New tests can be simply defined in testcases/ dir providing a proper struct
+  tdescr overriding all the defaults we wish to change (as of now providing a
+  custom run method is mandatory though)
+
+- Signals' test-cases hereafter defined belong currently to two
+  principal families:
+
+  - 'mangle_' tests: a real signal (SIGUSR1) is raised and used as a trigger
+    and then the test case code modifies the signal frame from inside the
+    signal handler itself.
+
+  - 'fake_sigreturn_' tests: a brand new custom artificial sigframe structure
+    is placed on the stack and a sigreturn syscall is called to simulate a
+    real signal return. This kind of tests does not use a trigger usually and
+    they are just fired using some simple included assembly trampoline code.
+
+ - Most of these tests are successfully passing if the process gets killed by
+   some fatal signal: usually SIGSEGV or SIGBUS. Since while writing this
+   kind of tests it is extremely easy in fact to end-up injecting other
+   unrelated SEGV bugs in the testcases, it becomes extremely tricky to
+   be really sure that the tests are really addressing what they are meant
+   to address and they are not instead falling apart due to unplanned bugs
+   in the test code.
+   In order to alleviate the misery of the life of such test-developer, a few
+   helpers are provided:
+
+   - a couple of ASSERT_BAD/GOOD_CONTEXT() macros to easily parse a ucontext_t
+     and verify if it is indeed GOOD or BAD (depending on what we were
+     expecting), using the same logic/perspective as in the arm64 Kernel signals
+     routines.
+
+   - a sanity mechanism to be used in 'fake_sigreturn_'-alike tests: enabled by
+     default it takes care to verify that the test-execution had at least
+     successfully progressed up to the stage of triggering the fake sigreturn
+     call.
+
+  In both cases test results are expected in terms of:
+   - some fatal signal sent by the Kernel to the test process
+  or
+  - analyzing some final regs state

tools/testing/selftests/arm64/signal/test_signals.c

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 ARM Limited
+ *
+ * Generic test wrapper for arm64 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;
+
+int main(int argc, char *argv[])
+{
+	current = &tde;
+
+	ksft_print_msg("%s :: %s\n", current->name, current->descr);
+	if (test_setup(current)) {
+		test_run(current);
+		test_result(current);
+		test_cleanup(current);
+	}
+
+	return current->pass ? KSFT_PASS : KSFT_FAIL;
+}

tools/testing/selftests/arm64/signal/test_signals.h

@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2019 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 installed by KSFT
+ * framework since we asked for it by setting flag KSFT_KHDR_INSTALL
+ * in our Makefile.
+ */
+#include <asm/ptrace.h>
+#include <asm/hwcap.h>
+
+#define __stringify_1(x...)	#x
+#define __stringify(x...)	__stringify_1(x)
+
+#define get_regval(regname, out)			\
+{							\
+	asm volatile("mrs %0, " __stringify(regname)	\
+	: "=r" (out)					\
+	:						\
+	: "memory");					\
+}
+
+/*
+ * Feature flags used in tdescr.feats_required to specify
+ * any feature by the test
+ */
+enum {
+	FSSBS_BIT,
+	FMAX_END
+};
+
+#define FEAT_SSBS		(1UL << FSSBS_BIT)
+
+/*
+ * 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;
+	unsigned long		feats_required;
+	/* bitmask of effectively supported feats: populated at run-time */
+	unsigned long		feats_supported;
+	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;
+	/* optional sa_flags for the installed handler */
+	int			sa_flags;
+	ucontext_t		saved_uc;
+	/* optional test private data */
+	void                    *priv;
+
+	/* a custom setup function to be called before test starts */
+	int (*setup)(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 test starting */
+	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