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