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https://github.com/jart/cosmopolitan.git
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4631d34d0d
It's now possible to use sigaltstack() to recover from stack overflows on Windows. Several bugs in sigaltstack() have been fixed, for all our supported platforms. There's a newer better example showing how to use this, along with three independent unit tests just to further showcase the various techniques.
105 lines
4.2 KiB
C
105 lines
4.2 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/struct/sigaction.h"
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#include "libc/calls/struct/sigaltstack.h"
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#include "libc/calls/struct/siginfo.h"
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#include "libc/dce.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/limits.h"
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#include "libc/mem/gc.internal.h"
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#include "libc/mem/mem.h"
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#include "libc/runtime/runtime.h"
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#include "libc/runtime/sysconf.h"
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#include "libc/sysv/consts/sa.h"
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#include "libc/sysv/consts/sig.h"
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#include "libc/sysv/consts/ss.h"
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#include "libc/testlib/testlib.h"
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#include "libc/thread/thread.h"
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/**
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* stack overflow recovery technique #2
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* longjmp out of signal back into thread
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* simple but it can upset kernels / libraries
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*/
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jmp_buf recover;
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volatile bool smashed_stack;
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void CrashHandler(int sig, siginfo_t *si, void *ctx) {
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struct sigaltstack ss;
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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ASSERT_EQ(SS_ONSTACK, ss.ss_flags);
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kprintf("kprintf avoids overflowing %G %p\n", si->si_signo, si->si_addr);
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smashed_stack = true;
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ASSERT_TRUE(__is_stack_overflow(si, ctx));
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longjmp(recover, 123);
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}
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int StackOverflow(int f(), int n) {
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if (n < INT_MAX) {
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return f(f, n + 1) - 1;
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} else {
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return INT_MAX;
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}
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}
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int (*pStackOverflow)(int (*)(), int) = StackOverflow;
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void *MyPosixThread(void *arg) {
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int jumpcode;
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struct sigaction sa, o1, o2;
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struct sigaltstack ss;
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ss.ss_flags = 0;
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ss.ss_size = sysconf(_SC_MINSIGSTKSZ) + 4096;
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ss.ss_sp = gc(malloc(ss.ss_size));
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ASSERT_SYS(0, 0, sigaltstack(&ss, 0));
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sa.sa_flags = SA_SIGINFO | SA_ONSTACK; // <-- important
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sigemptyset(&sa.sa_mask);
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sa.sa_sigaction = CrashHandler;
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sigaction(SIGBUS, &sa, &o1);
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sigaction(SIGSEGV, &sa, &o2);
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if (!(jumpcode = setjmp(recover))) {
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exit(pStackOverflow(pStackOverflow, 0));
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}
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ASSERT_EQ(123, jumpcode);
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sigaction(SIGSEGV, &o2, 0);
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sigaction(SIGBUS, &o1, 0);
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// here's where longjmp() gets us into trouble
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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if (IsXnu() || IsNetbsd()) {
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ASSERT_EQ(SS_ONSTACK, ss.ss_flags); // wut
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} else {
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ASSERT_EQ(0, ss.ss_flags);
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}
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return 0;
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}
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TEST(stackoverflow, standardStack_altStack_thread_longjmp) {
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pthread_t th;
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struct sigaltstack ss;
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for (int i = 0; i < 2; ++i) {
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smashed_stack = false;
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pthread_create(&th, 0, MyPosixThread, 0);
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pthread_join(th, 0);
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ASSERT_TRUE(smashed_stack);
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// this should be SS_DISABLE but ShowCrashReports() creates an alt stack
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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ASSERT_EQ(0, ss.ss_flags);
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}
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}
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