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