arm64/signal/test_signals_utils.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 /* Copyright (C) 2019 ARM Limited */
0003
0004 #ifndef __TEST_SIGNALS_UTILS_H__
0005 #define __TEST_SIGNALS_UTILS_H__
0006
0007 #include <assert.h>
0008 #include <stdio.h>
0009 #include <string.h>
0010
0011 #include "test_signals.h"
0012
0013 int test_init(struct tdescr *td);
0014 int test_setup(struct tdescr *td);
0015 void test_cleanup(struct tdescr *td);
0016 int test_run(struct tdescr *td);
0017 void test_result(struct tdescr *td);
0018
0019 static inline bool feats_ok(struct tdescr *td)
0020 {
0021     if (td->feats_incompatible & td->feats_supported)
0022         return false;
0023     return (td->feats_required & td->feats_supported) == td->feats_required;
0024 }
0025
0026 /*
0027  * Obtaining a valid and full-blown ucontext_t from userspace is tricky:
0028  * libc getcontext does() not save all the regs and messes with some of
0029  * them (pstate value in particular is not reliable).
0030  *
0031  * Here we use a service signal to grab the ucontext_t from inside a
0032  * dedicated signal handler, since there, it is populated by Kernel
0033  * itself in setup_sigframe(). The grabbed context is then stored and
0034  * made available in td->live_uc.
0035  *
0036  * As service-signal is used a SIGTRAP induced by a 'brk' instruction,
0037  * because here we have to avoid syscalls to trigger the signal since
0038  * they would cause any SVE sigframe content (if any) to be removed.
0039  *
0040  * Anyway this function really serves a dual purpose:
0041  *
0042  * 1. grab a valid sigcontext into td->live_uc for result analysis: in
0043  * such case it returns 1.
0044  *
0045  * 2. detect if, somehow, a previously grabbed live_uc context has been
0046  * used actively with a sigreturn: in such a case the execution would have
0047  * magically resumed in the middle of this function itself (seen_already==1):
0048  * in such a case return 0, since in fact we have not just simply grabbed
0049  * the context.
0050  *
0051  * This latter case is useful to detect when a fake_sigreturn test-case has
0052  * unexpectedly survived without hitting a SEGV.
0053  *
0054  * Note that the case of runtime dynamically sized sigframes (like in SVE
0055  * context) is still NOT addressed: sigframe size is supposed to be fixed
0056  * at sizeof(ucontext_t).
0057  */
0058 static __always_inline bool get_current_context(struct tdescr *td,
0059                         ucontext_t *dest_uc)
0060 {
0061     static volatile bool seen_already;
0062
0063     assert(td && dest_uc);
0064     /* it's a genuine invocation..reinit */
0065     seen_already = 0;
0066     td->live_uc_valid = 0;
0067     td->live_sz = sizeof(*dest_uc);
0068     memset(dest_uc, 0x00, td->live_sz);
0069     td->live_uc = dest_uc;
0070     /*
0071      * Grab ucontext_t triggering a SIGTRAP.
0072      *
0073      * Note that:
0074      * - live_uc_valid is declared volatile sig_atomic_t in
0075      *   struct tdescr since it will be changed inside the
0076      *   sig_copyctx handler
0077      * - the additional 'memory' clobber is there to avoid possible
0078      *   compiler's assumption on live_uc_valid and the content
0079      *   pointed by dest_uc, which are all changed inside the signal
0080      *   handler
0081      * - BRK causes a debug exception which is handled by the Kernel
0082      *   and finally causes the SIGTRAP signal to be delivered to this
0083      *   test thread. Since such delivery happens on the ret_to_user()
0084      *   /do_notify_resume() debug exception return-path, we are sure
0085      *   that the registered SIGTRAP handler has been run to completion
0086      *   before the execution path is restored here: as a consequence
0087      *   we can be sure that the volatile sig_atomic_t live_uc_valid
0088      *   carries a meaningful result. Being in a single thread context
0089      *   we'll also be sure that any access to memory modified by the
0090      *   handler (namely ucontext_t) will be visible once returned.
0091      * - note that since we are using a breakpoint instruction here
0092      *   to cause a SIGTRAP, the ucontext_t grabbed from the signal
0093      *   handler would naturally contain a PC pointing exactly to this
0094      *   BRK line, which means that, on return from the signal handler,
0095      *   or if we place the ucontext_t on the stack to fake a sigreturn,
0096      *   we'll end up in an infinite loop of BRK-SIGTRAP-handler.
0097      *   For this reason we take care to artificially move forward the
0098      *   PC to the next instruction while inside the signal handler.
0099      */
0100     asm volatile ("brk #666"
0101               : "+m" (*dest_uc)
0102               :
0103               : "memory");
0104
0105     /*
0106      * If we get here with seen_already==1 it implies the td->live_uc
0107      * context has been used to get back here....this probably means
0108      * a test has failed to cause a SEGV...anyway live_uc does not
0109      * point to a just acquired copy of ucontext_t...so return 0
0110      */
0111     if (seen_already) {
0112         fprintf(stdout,
0113             "Unexpected successful sigreturn detected: live_uc is stale !\n");
0114         return 0;
0115     }
0116     seen_already = 1;
0117
0118     return td->live_uc_valid;
0119 }
0120
0121 int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes);
0122 #endif