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 if (td->feats_incompatible & td->feats_supported) 22 return false; 23 return (td->feats_required & td->feats_supported) == td->feats_required; 24 } 25 26 /* 27 * Obtaining a valid and full-blown ucontext_t from userspace is tricky: 28 * libc getcontext does() not save all the regs and messes with some of 29 * them (pstate value in particular is not reliable). 30 * 31 * Here we use a service signal to grab the ucontext_t from inside a 32 * dedicated signal handler, since there, it is populated by Kernel 33 * itself in setup_sigframe(). The grabbed context is then stored and 34 * made available in td->live_uc. 35 * 36 * As service-signal is used a SIGTRAP induced by a 'brk' instruction, 37 * because here we have to avoid syscalls to trigger the signal since 38 * they would cause any SVE sigframe content (if any) to be removed. 39 * 40 * Anyway this function really serves a dual purpose: 41 * 42 * 1. grab a valid sigcontext into td->live_uc for result analysis: in 43 * such case it returns 1. 44 * 45 * 2. detect if, somehow, a previously grabbed live_uc context has been 46 * used actively with a sigreturn: in such a case the execution would have 47 * magically resumed in the middle of this function itself (seen_already==1): 48 * in such a case return 0, since in fact we have not just simply grabbed 49 * the context. 50 * 51 * This latter case is useful to detect when a fake_sigreturn test-case has 52 * unexpectedly survived without hitting a SEGV. 53 * 54 * Note that the case of runtime dynamically sized sigframes (like in SVE 55 * context) is still NOT addressed: sigframe size is supposed to be fixed 56 * at sizeof(ucontext_t). 57 */ 58 static __always_inline bool get_current_context(struct tdescr *td, 59 ucontext_t *dest_uc, 60 size_t dest_sz) 61 { 62 static volatile bool seen_already; 63 64 assert(td && dest_uc); 65 /* it's a genuine invocation..reinit */ 66 seen_already = 0; 67 td->live_uc_valid = 0; 68 td->live_sz = dest_sz; 69 memset(dest_uc, 0x00, td->live_sz); 70 td->live_uc = dest_uc; 71 /* 72 * Grab ucontext_t triggering a SIGTRAP. 73 * 74 * Note that: 75 * - live_uc_valid is declared volatile sig_atomic_t in 76 * struct tdescr since it will be changed inside the 77 * sig_copyctx handler 78 * - the additional 'memory' clobber is there to avoid possible 79 * compiler's assumption on live_uc_valid and the content 80 * pointed by dest_uc, which are all changed inside the signal 81 * handler 82 * - BRK causes a debug exception which is handled by the Kernel 83 * and finally causes the SIGTRAP signal to be delivered to this 84 * test thread. Since such delivery happens on the ret_to_user() 85 * /do_notify_resume() debug exception return-path, we are sure 86 * that the registered SIGTRAP handler has been run to completion 87 * before the execution path is restored here: as a consequence 88 * we can be sure that the volatile sig_atomic_t live_uc_valid 89 * carries a meaningful result. Being in a single thread context 90 * we'll also be sure that any access to memory modified by the 91 * handler (namely ucontext_t) will be visible once returned. 92 * - note that since we are using a breakpoint instruction here 93 * to cause a SIGTRAP, the ucontext_t grabbed from the signal 94 * handler would naturally contain a PC pointing exactly to this 95 * BRK line, which means that, on return from the signal handler, 96 * or if we place the ucontext_t on the stack to fake a sigreturn, 97 * we'll end up in an infinite loop of BRK-SIGTRAP-handler. 98 * For this reason we take care to artificially move forward the 99 * PC to the next instruction while inside the signal handler. 100 */ 101 asm volatile ("brk #666" 102 : "+m" (*dest_uc) 103 : 104 : "memory"); 105 106 /* 107 * If we get here with seen_already==1 it implies the td->live_uc 108 * context has been used to get back here....this probably means 109 * a test has failed to cause a SEGV...anyway live_uc does not 110 * point to a just acquired copy of ucontext_t...so return 0 111 */ 112 if (seen_already) { 113 fprintf(stdout, 114 "Unexpected successful sigreturn detected: live_uc is stale !\n"); 115 return 0; 116 } 117 seen_already = 1; 118 119 return td->live_uc_valid; 120 } 121 122 int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes); 123 #endif 124