test_signals_utils.h (4601B)
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 13int test_init(struct tdescr *td); 14int test_setup(struct tdescr *td); 15void test_cleanup(struct tdescr *td); 16int test_run(struct tdescr *td); 17void test_result(struct tdescr *td); 18 19static 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 */ 58static __always_inline bool get_current_context(struct tdescr *td, 59 ucontext_t *dest_uc) 60{ 61 static volatile bool seen_already; 62 63 assert(td && dest_uc); 64 /* it's a genuine invocation..reinit */ 65 seen_already = 0; 66 td->live_uc_valid = 0; 67 td->live_sz = sizeof(*dest_uc); 68 memset(dest_uc, 0x00, td->live_sz); 69 td->live_uc = dest_uc; 70 /* 71 * Grab ucontext_t triggering a SIGTRAP. 72 * 73 * Note that: 74 * - live_uc_valid is declared volatile sig_atomic_t in 75 * struct tdescr since it will be changed inside the 76 * sig_copyctx handler 77 * - the additional 'memory' clobber is there to avoid possible 78 * compiler's assumption on live_uc_valid and the content 79 * pointed by dest_uc, which are all changed inside the signal 80 * handler 81 * - BRK causes a debug exception which is handled by the Kernel 82 * and finally causes the SIGTRAP signal to be delivered to this 83 * test thread. Since such delivery happens on the ret_to_user() 84 * /do_notify_resume() debug exception return-path, we are sure 85 * that the registered SIGTRAP handler has been run to completion 86 * before the execution path is restored here: as a consequence 87 * we can be sure that the volatile sig_atomic_t live_uc_valid 88 * carries a meaningful result. Being in a single thread context 89 * we'll also be sure that any access to memory modified by the 90 * handler (namely ucontext_t) will be visible once returned. 91 * - note that since we are using a breakpoint instruction here 92 * to cause a SIGTRAP, the ucontext_t grabbed from the signal 93 * handler would naturally contain a PC pointing exactly to this 94 * BRK line, which means that, on return from the signal handler, 95 * or if we place the ucontext_t on the stack to fake a sigreturn, 96 * we'll end up in an infinite loop of BRK-SIGTRAP-handler. 97 * For this reason we take care to artificially move forward the 98 * PC to the next instruction while inside the signal handler. 99 */ 100 asm volatile ("brk #666" 101 : "+m" (*dest_uc) 102 : 103 : "memory"); 104 105 /* 106 * If we get here with seen_already==1 it implies the td->live_uc 107 * context has been used to get back here....this probably means 108 * a test has failed to cause a SEGV...anyway live_uc does not 109 * point to a just acquired copy of ucontext_t...so return 0 110 */ 111 if (seen_already) { 112 fprintf(stdout, 113 "Unexpected successful sigreturn detected: live_uc is stale !\n"); 114 return 0; 115 } 116 seen_already = 1; 117 118 return td->live_uc_valid; 119} 120 121int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes); 122#endif