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 "test_signals.h" 12 13 int test_init(struct tdescr *td); 14 int test_setup(struct tdescr *td); 15 void test_cleanup(struct tdescr *td); 16 int test_run(struct tdescr *td); 17 void test_result(struct tdescr *td); 18 19 static inline bool feats_ok(struct tdescr *td) 20 { 21 return (td->feats_required & td->feats_supported) == td->feats_required; 22 } 23 24 /* 25 * Obtaining a valid and full-blown ucontext_t from userspace is tricky: 26 * libc getcontext does() not save all the regs and messes with some of 27 * them (pstate value in particular is not reliable). 28 * 29 * Here we use a service signal to grab the ucontext_t from inside a 30 * dedicated signal handler, since there, it is populated by Kernel 31 * itself in setup_sigframe(). The grabbed context is then stored and 32 * made available in td->live_uc. 33 * 34 * As service-signal is used a SIGTRAP induced by a 'brk' instruction, 35 * because here we have to avoid syscalls to trigger the signal since 36 * they would cause any SVE sigframe content (if any) to be removed. 37 * 38 * Anyway this function really serves a dual purpose: 39 * 40 * 1. grab a valid sigcontext into td->live_uc for result analysis: in 41 * such case it returns 1. 42 * 43 * 2. detect if, somehow, a previously grabbed live_uc context has been 44 * used actively with a sigreturn: in such a case the execution would have 45 * magically resumed in the middle of this function itself (seen_already==1): 46 * in such a case return 0, since in fact we have not just simply grabbed 47 * the context. 48 * 49 * This latter case is useful to detect when a fake_sigreturn test-case has 50 * unexpectedly survived without hitting a SEGV. 51 * 52 * Note that the case of runtime dynamically sized sigframes (like in SVE 53 * context) is still NOT addressed: sigframe size is supposed to be fixed 54 * at sizeof(ucontext_t). 55 */ 56 static __always_inline bool get_current_context(struct tdescr *td, 57 ucontext_t *dest_uc) 58 { 59 static volatile bool seen_already; 60 61 assert(td && dest_uc); 62 /* it's a genuine invocation..reinit */ 63 seen_already = 0; 64 td->live_uc_valid = 0; 65 td->live_sz = sizeof(*dest_uc); 66 memset(dest_uc, 0x00, td->live_sz); 67 td->live_uc = dest_uc; 68 /* 69 * Grab ucontext_t triggering a SIGTRAP. 70 * 71 * Note that: 72 * - live_uc_valid is declared volatile sig_atomic_t in 73 * struct tdescr since it will be changed inside the 74 * sig_copyctx handler 75 * - the additional 'memory' clobber is there to avoid possible 76 * compiler's assumption on live_uc_valid and the content 77 * pointed by dest_uc, which are all changed inside the signal 78 * handler 79 * - BRK causes a debug exception which is handled by the Kernel 80 * and finally causes the SIGTRAP signal to be delivered to this 81 * test thread. Since such delivery happens on the ret_to_user() 82 * /do_notify_resume() debug exception return-path, we are sure 83 * that the registered SIGTRAP handler has been run to completion 84 * before the execution path is restored here: as a consequence 85 * we can be sure that the volatile sig_atomic_t live_uc_valid 86 * carries a meaningful result. Being in a single thread context 87 * we'll also be sure that any access to memory modified by the 88 * handler (namely ucontext_t) will be visible once returned. 89 * - note that since we are using a breakpoint instruction here 90 * to cause a SIGTRAP, the ucontext_t grabbed from the signal 91 * handler would naturally contain a PC pointing exactly to this 92 * BRK line, which means that, on return from the signal handler, 93 * or if we place the ucontext_t on the stack to fake a sigreturn, 94 * we'll end up in an infinite loop of BRK-SIGTRAP-handler. 95 * For this reason we take care to artificially move forward the 96 * PC to the next instruction while inside the signal handler. 97 */ 98 asm volatile ("brk #666" 99 : "+m" (*dest_uc) 100 : 101 : "memory"); 102 103 /* 104 * If we get here with seen_already==1 it implies the td->live_uc 105 * context has been used to get back here....this probably means 106 * a test has failed to cause a SEGV...anyway live_uc does not 107 * point to a just acquired copy of ucontext_t...so return 0 108 */ 109 if (seen_already) { 110 fprintf(stdout, 111 "Unexpected successful sigreturn detected: live_uc is stale !\n"); 112 return 0; 113 } 114 seen_already = 1; 115 116 return td->live_uc_valid; 117 } 118 119 int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes); 120 #endif 121