121 lines
4.4 KiB
C
121 lines
4.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright (C) 2019 ARM Limited */
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#ifndef __TEST_SIGNALS_UTILS_H__
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#define __TEST_SIGNALS_UTILS_H__
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#include <assert.h>
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#include <stdio.h>
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#include <string.h>
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#include "test_signals.h"
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int test_init(struct tdescr *td);
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int test_setup(struct tdescr *td);
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void test_cleanup(struct tdescr *td);
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int test_run(struct tdescr *td);
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void test_result(struct tdescr *td);
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static inline bool feats_ok(struct tdescr *td)
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{
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return (td->feats_required & td->feats_supported) == td->feats_required;
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}
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/*
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* Obtaining a valid and full-blown ucontext_t from userspace is tricky:
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* libc getcontext does() not save all the regs and messes with some of
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* them (pstate value in particular is not reliable).
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*
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* Here we use a service signal to grab the ucontext_t from inside a
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* dedicated signal handler, since there, it is populated by Kernel
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* itself in setup_sigframe(). The grabbed context is then stored and
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* made available in td->live_uc.
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*
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* As service-signal is used a SIGTRAP induced by a 'brk' instruction,
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* because here we have to avoid syscalls to trigger the signal since
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* they would cause any SVE sigframe content (if any) to be removed.
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*
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* Anyway this function really serves a dual purpose:
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*
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* 1. grab a valid sigcontext into td->live_uc for result analysis: in
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* such case it returns 1.
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*
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* 2. detect if, somehow, a previously grabbed live_uc context has been
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* used actively with a sigreturn: in such a case the execution would have
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* magically resumed in the middle of this function itself (seen_already==1):
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* in such a case return 0, since in fact we have not just simply grabbed
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* the context.
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*
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* This latter case is useful to detect when a fake_sigreturn test-case has
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* unexpectedly survived without hitting a SEGV.
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*
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* Note that the case of runtime dynamically sized sigframes (like in SVE
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* context) is still NOT addressed: sigframe size is supposed to be fixed
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* at sizeof(ucontext_t).
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*/
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static __always_inline bool get_current_context(struct tdescr *td,
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ucontext_t *dest_uc)
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{
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static volatile bool seen_already;
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assert(td && dest_uc);
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/* it's a genuine invocation..reinit */
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seen_already = 0;
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td->live_uc_valid = 0;
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td->live_sz = sizeof(*dest_uc);
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memset(dest_uc, 0x00, td->live_sz);
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td->live_uc = dest_uc;
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/*
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* Grab ucontext_t triggering a SIGTRAP.
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*
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* Note that:
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* - live_uc_valid is declared volatile sig_atomic_t in
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* struct tdescr since it will be changed inside the
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* sig_copyctx handler
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* - the additional 'memory' clobber is there to avoid possible
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* compiler's assumption on live_uc_valid and the content
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* pointed by dest_uc, which are all changed inside the signal
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* handler
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* - BRK causes a debug exception which is handled by the Kernel
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* and finally causes the SIGTRAP signal to be delivered to this
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* test thread. Since such delivery happens on the ret_to_user()
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* /do_notify_resume() debug exception return-path, we are sure
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* that the registered SIGTRAP handler has been run to completion
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* before the execution path is restored here: as a consequence
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* we can be sure that the volatile sig_atomic_t live_uc_valid
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* carries a meaningful result. Being in a single thread context
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* we'll also be sure that any access to memory modified by the
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* handler (namely ucontext_t) will be visible once returned.
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* - note that since we are using a breakpoint instruction here
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* to cause a SIGTRAP, the ucontext_t grabbed from the signal
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* handler would naturally contain a PC pointing exactly to this
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* BRK line, which means that, on return from the signal handler,
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* or if we place the ucontext_t on the stack to fake a sigreturn,
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* we'll end up in an infinite loop of BRK-SIGTRAP-handler.
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* For this reason we take care to artificially move forward the
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* PC to the next instruction while inside the signal handler.
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*/
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asm volatile ("brk #666"
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: "+m" (*dest_uc)
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:
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: "memory");
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/*
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* If we get here with seen_already==1 it implies the td->live_uc
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* context has been used to get back here....this probably means
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* a test has failed to cause a SEGV...anyway live_uc does not
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* point to a just acquired copy of ucontext_t...so return 0
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*/
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if (seen_already) {
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fprintf(stdout,
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"Unexpected successful sigreturn detected: live_uc is stale !\n");
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return 0;
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}
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seen_already = 1;
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return td->live_uc_valid;
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}
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int fake_sigreturn(void *sigframe, size_t sz, int misalign_bytes);
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#endif
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