LXR linux/tools/testing/selftests/arm64/signal/test_signals

   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        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 */
  56static __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
 119int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes);
 120#endif
 121