test_signals_utils.h

  1/* SPDX-License-Identifier: GPL-2.0 */
  2/* Copyright (C) 2019 ARM Limited */
  3
  4#ifndef __TEST_SIGNALS_UTILS_H__
  5#define __TEST_SIGNALS_UTILS_H__
  6
  7#include <assert.h>
  8#include <stdio.h>
  9#include <stdint.h>
 10#include <string.h>
 11
 12#include <linux/compiler.h>
 13
 14#include "test_signals.h"
 15
 16int test_init(struct tdescr *td);
 17int test_setup(struct tdescr *td);
 18void test_cleanup(struct tdescr *td);
 19int test_run(struct tdescr *td);
 20void test_result(struct tdescr *td);
 21
 22#ifndef __NR_prctl
 23#define __NR_prctl 167
 24#endif
 25
 26/*
 27 * The prctl takes 1 argument but we need to ensure that the other
 28 * values passed in registers to the syscall are zero since the kernel
 29 * validates them.
 30 */
 31#define gcs_set_state(state)					\
 32	({								\
 33		register long _num  __asm__ ("x8") = __NR_prctl;	\
 34		register long _arg1 __asm__ ("x0") =  PR_SET_SHADOW_STACK_STATUS; \
 35		register long _arg2 __asm__ ("x1") = (long)(state);	\
 36		register long _arg3 __asm__ ("x2") = 0;			\
 37		register long _arg4 __asm__ ("x3") = 0;			\
 38		register long _arg5 __asm__ ("x4") = 0;			\
 39	                                                                      \
 40		__asm__  volatile (					\
 41			"svc #0\n"					\
 42			: "=r"(_arg1)					\
 43			: "r"(_arg1), "r"(_arg2),			\
 44			  "r"(_arg3), "r"(_arg4),			\
 45			  "r"(_arg5), "r"(_num)				\
 46			: "memory", "cc"				\
 47			);						\
 48		_arg1;							\
 49	})
 50
 51static inline __attribute__((always_inline)) uint64_t get_gcspr_el0(void)
 52{
 53	uint64_t val;
 54
 55	asm volatile("mrs %0, S3_3_C2_C5_1" : "=r" (val));
 56
 57	return val;
 58}
 59
 60static inline bool feats_ok(struct tdescr *td)
 61{
 62	if (td->feats_incompatible & td->feats_supported)
 63		return false;
 64	return (td->feats_required & td->feats_supported) == td->feats_required;
 65}
 66
 67/*
 68 * Obtaining a valid and full-blown ucontext_t from userspace is tricky:
 69 * libc getcontext does() not save all the regs and messes with some of
 70 * them (pstate value in particular is not reliable).
 71 *
 72 * Here we use a service signal to grab the ucontext_t from inside a
 73 * dedicated signal handler, since there, it is populated by Kernel
 74 * itself in setup_sigframe(). The grabbed context is then stored and
 75 * made available in td->live_uc.
 76 *
 77 * As service-signal is used a SIGTRAP induced by a 'brk' instruction,
 78 * because here we have to avoid syscalls to trigger the signal since
 79 * they would cause any SVE sigframe content (if any) to be removed.
 80 *
 81 * Anyway this function really serves a dual purpose:
 82 *
 83 * 1. grab a valid sigcontext into td->live_uc for result analysis: in
 84 * such case it returns 1.
 85 *
 86 * 2. detect if, somehow, a previously grabbed live_uc context has been
 87 * used actively with a sigreturn: in such a case the execution would have
 88 * magically resumed in the middle of this function itself (seen_already==1):
 89 * in such a case return 0, since in fact we have not just simply grabbed
 90 * the context.
 91 *
 92 * This latter case is useful to detect when a fake_sigreturn test-case has
 93 * unexpectedly survived without hitting a SEGV.
 94 *
 95 * Note that the case of runtime dynamically sized sigframes (like in SVE
 96 * context) is still NOT addressed: sigframe size is supposed to be fixed
 97 * at sizeof(ucontext_t).
 98 */
 99static __always_inline bool get_current_context(struct tdescr *td,
100						ucontext_t *dest_uc,
101						size_t dest_sz)
102{
103	static volatile bool seen_already;
104	int i;
105	char *uc = (char *)dest_uc;
106
107	assert(td && dest_uc);
108	/* it's a genuine invocation..reinit */
109	seen_already = 0;
110	td->live_uc_valid = 0;
111	td->live_sz = dest_sz;
112
113	/*
114	 * This is a memset() but we don't want the compiler to
115	 * optimise it into either instructions or a library call
116	 * which might be incompatible with streaming mode.
117	 */
118	for (i = 0; i < td->live_sz; i++) {
119		uc[i] = 0;
120		OPTIMIZER_HIDE_VAR(uc[0]);
121	}
122
123	td->live_uc = dest_uc;
124	/*
125	 * Grab ucontext_t triggering a SIGTRAP.
126	 *
127	 * Note that:
128	 * - live_uc_valid is declared volatile sig_atomic_t in
129	 *   struct tdescr since it will be changed inside the
130	 *   sig_copyctx handler
131	 * - the additional 'memory' clobber is there to avoid possible
132	 *   compiler's assumption on live_uc_valid and the content
133	 *   pointed by dest_uc, which are all changed inside the signal
134	 *   handler
135	 * - BRK causes a debug exception which is handled by the Kernel
136	 *   and finally causes the SIGTRAP signal to be delivered to this
137	 *   test thread. Since such delivery happens on the ret_to_user()
138	 *   /do_notify_resume() debug exception return-path, we are sure
139	 *   that the registered SIGTRAP handler has been run to completion
140	 *   before the execution path is restored here: as a consequence
141	 *   we can be sure that the volatile sig_atomic_t live_uc_valid
142	 *   carries a meaningful result. Being in a single thread context
143	 *   we'll also be sure that any access to memory modified by the
144	 *   handler (namely ucontext_t) will be visible once returned.
145	 * - note that since we are using a breakpoint instruction here
146	 *   to cause a SIGTRAP, the ucontext_t grabbed from the signal
147	 *   handler would naturally contain a PC pointing exactly to this
148	 *   BRK line, which means that, on return from the signal handler,
149	 *   or if we place the ucontext_t on the stack to fake a sigreturn,
150	 *   we'll end up in an infinite loop of BRK-SIGTRAP-handler.
151	 *   For this reason we take care to artificially move forward the
152	 *   PC to the next instruction while inside the signal handler.
153	 */
154	asm volatile ("brk #666"
155		      : "+m" (*dest_uc)
156		      :
157		      : "memory");
158
159	/*
160	 * If we were grabbing a streaming mode context then we may
161	 * have entered streaming mode behind the system's back and
162	 * libc or compiler generated code might decide to do
163	 * something invalid in streaming mode, or potentially even
164	 * the state of ZA.  Issue a SMSTOP to exit both now we have
165	 * grabbed the state.
166	 */
167	if (td->feats_supported & FEAT_SME)
168		asm volatile("msr S0_3_C4_C6_3, xzr");
169
170	/*
171	 * If we get here with seen_already==1 it implies the td->live_uc
172	 * context has been used to get back here....this probably means
173	 * a test has failed to cause a SEGV...anyway live_uc does not
174	 * point to a just acquired copy of ucontext_t...so return 0
175	 */
176	if (seen_already) {
177		fprintf(stdout,
178			"Unexpected successful sigreturn detected: live_uc is stale !\n");
179		return 0;
180	}
181	seen_already = 1;
182
183	return td->live_uc_valid;
184}
185
186int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes);
187#endif