tools/testing/selftests/arm64/signal/test_signals_utils.h

   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