kselftest/arm64: Add GCS signal tests

Do some testing of the signal handling for GCS, checking that a GCS
frame has the expected information in it and that the expected signals
are delivered with invalid operations.

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Tested-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20241001-arm64-gcs-v13-37-222b78d87eee@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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

@@ -3,6 +3,7 @@ mangle_*
 fake_sigreturn_*
 fpmr_*
 poe_*
+gcs_*
 sme_*
 ssve_*
 sve_*

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

@@ -6,6 +6,7 @@
 
 #include <assert.h>
 #include <stdio.h>
+#include <stdint.h>
 #include <string.h>
 
 #include <linux/compiler.h>
@@ -47,6 +48,15 @@ void test_result(struct tdescr *td);
 		_arg1;							\
 	})
 
+static inline __attribute__((always_inline)) uint64_t get_gcspr_el0(void)
+{
+	uint64_t val;
+
+	asm volatile("mrs %0, S3_3_C2_C5_1" : "=r" (val));
+
+	return val;
+}
+
 static inline bool feats_ok(struct tdescr *td)
 {
 	if (td->feats_incompatible & td->feats_supported)

tools/testing/selftests/arm64/signal/testcases/gcs_exception_fault.c

@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 ARM Limited
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <unistd.h>
+
+#include <sys/mman.h>
+#include <sys/prctl.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+/*
+ * We should get this from asm/siginfo.h but the testsuite is being
+ * clever with redefining siginfo_t.
+ */
+#ifndef SEGV_CPERR
+#define SEGV_CPERR 10
+#endif
+
+static inline void gcsss1(uint64_t Xt)
+{
+	asm volatile (
+		"sys #3, C7, C7, #2, %0\n"
+		:
+		: "rZ" (Xt)
+		: "memory");
+}
+
+static int gcs_op_fault_trigger(struct tdescr *td)
+{
+	/*
+	 * The slot below our current GCS should be in a valid GCS but
+	 * must not have a valid cap in it.
+	 */
+	gcsss1(get_gcspr_el0() - 8);
+
+	return 0;
+}
+
+static int gcs_op_fault_signal(struct tdescr *td, siginfo_t *si,
+				  ucontext_t *uc)
+{
+	ASSERT_GOOD_CONTEXT(uc);
+
+	return 1;
+}
+
+struct tdescr tde = {
+	.name = "Invalid GCS operation",
+	.descr = "An invalid GCS operation generates the expected signal",
+	.feats_required = FEAT_GCS,
+	.timeout = 3,
+	.sig_ok = SIGSEGV,
+	.sig_ok_code = SEGV_CPERR,
+	.sanity_disabled = true,
+	.trigger = gcs_op_fault_trigger,
+	.run = gcs_op_fault_signal,
+};

tools/testing/selftests/arm64/signal/testcases/gcs_frame.c

@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 ARM Limited
+ */
+
+#include <signal.h>
+#include <ucontext.h>
+#include <sys/prctl.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+static union {
+	ucontext_t uc;
+	char buf[1024 * 64];
+} context;
+
+static int gcs_regs(struct tdescr *td, siginfo_t *si, ucontext_t *uc)
+{
+	size_t offset;
+	struct _aarch64_ctx *head = GET_BUF_RESV_HEAD(context);
+	struct gcs_context *gcs;
+	unsigned long expected, gcspr;
+	uint64_t *u64_val;
+	int ret;
+
+	ret = prctl(PR_GET_SHADOW_STACK_STATUS, &expected, 0, 0, 0);
+	if (ret != 0) {
+		fprintf(stderr, "Unable to query GCS status\n");
+		return 1;
+	}
+
+	/* We expect a cap to be added to the GCS in the signal frame */
+	gcspr = get_gcspr_el0();
+	gcspr -= 8;
+	fprintf(stderr, "Expecting GCSPR_EL0 %lx\n", gcspr);
+
+	if (!get_current_context(td, &context.uc, sizeof(context))) {
+		fprintf(stderr, "Failed getting context\n");
+		return 1;
+	}
+
+	/* Ensure that the signal restore token was consumed */
+	u64_val = (uint64_t *)get_gcspr_el0() + 1;
+	if (*u64_val) {
+		fprintf(stderr, "GCS value at %p is %lx not 0\n",
+			u64_val, *u64_val);
+		return 1;
+	}
+
+	fprintf(stderr, "Got context\n");
+
+	head = get_header(head, GCS_MAGIC, GET_BUF_RESV_SIZE(context),
+			  &offset);
+	if (!head) {
+		fprintf(stderr, "No GCS context\n");
+		return 1;
+	}
+
+	gcs = (struct gcs_context *)head;
+
+	/* Basic size validation is done in get_current_context() */
+
+	if (gcs->features_enabled != expected) {
+		fprintf(stderr, "Features enabled %llx but expected %lx\n",
+			gcs->features_enabled, expected);
+		return 1;
+	}
+
+	if (gcs->gcspr != gcspr) {
+		fprintf(stderr, "Got GCSPR %llx but expected %lx\n",
+			gcs->gcspr, gcspr);
+		return 1;
+	}
+
+	fprintf(stderr, "GCS context validated\n");
+	td->pass = 1;
+
+	return 0;
+}
+
+struct tdescr tde = {
+	.name = "GCS basics",
+	.descr = "Validate a GCS signal context",
+	.feats_required = FEAT_GCS,
+	.timeout = 3,
+	.run = gcs_regs,
+};

tools/testing/selftests/arm64/signal/testcases/gcs_write_fault.c

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 ARM Limited
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <unistd.h>
+
+#include <sys/mman.h>
+#include <sys/prctl.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+static uint64_t *gcs_page;
+
+#ifndef __NR_map_shadow_stack
+#define __NR_map_shadow_stack 453
+#endif
+
+static bool alloc_gcs(struct tdescr *td)
+{
+	long page_size = sysconf(_SC_PAGE_SIZE);
+
+	gcs_page = (void *)syscall(__NR_map_shadow_stack, 0,
+				   page_size, 0);
+	if (gcs_page == MAP_FAILED) {
+		fprintf(stderr, "Failed to map %ld byte GCS: %d\n",
+			page_size, errno);
+		return false;
+	}
+
+	return true;
+}
+
+static int gcs_write_fault_trigger(struct tdescr *td)
+{
+	/* Verify that the page is readable (ie, not completely unmapped) */
+	fprintf(stderr, "Read value 0x%lx\n", gcs_page[0]);
+
+	/* A regular write should trigger a fault */
+	gcs_page[0] = EINVAL;
+
+	return 0;
+}
+
+static int gcs_write_fault_signal(struct tdescr *td, siginfo_t *si,
+				  ucontext_t *uc)
+{
+	ASSERT_GOOD_CONTEXT(uc);
+
+	return 1;
+}
+
+
+struct tdescr tde = {
+	.name = "GCS write fault",
+	.descr = "Normal writes to a GCS segfault",
+	.feats_required = FEAT_GCS,
+	.timeout = 3,
+	.sig_ok = SIGSEGV,
+	.sanity_disabled = true,
+	.init = alloc_gcs,
+	.trigger = gcs_write_fault_trigger,
+	.run = gcs_write_fault_signal,
+};