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
15 int test_init(struct tdescr *td);
16 int test_setup(struct tdescr *td);
17 void test_cleanup(struct tdescr *td);
18 int test_run(struct tdescr *td);
19 void test_result(struct tdescr *td);
20
21 static 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 */
60 static __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
147 int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes);
148 #endif
149
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