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379cd77078
On Windows, mmap() now chooses addresses transactionally. It reduces the risk of badness when interacting with the WIN32 memory manager. We don't throw darts anymore. There is also no more retry limit, since we recover from mystery maps more gracefully. The subroutine for combining adjacent maps has been rewritten for clarity. The print maps subroutine is better This change goes to great lengths to perfect the stack overflow code. On Windows you can now longjmp() out of a crash signal handler. Guard pages previously weren't being restored properly by the signal handler. That's fixed, so on Windows you can now handle a stack overflow multiple times. Great thought has been put into selecting the perfect SIGSTKSZ constants so you can save sigaltstack() memory. You can now use kprintf() with 512 bytes of stack available. The guard pages beneath the main stack are now recorded in the memory manager. This change fixes getcontext() so it works right with the %rax register.
136 lines
5.1 KiB
C
136 lines
5.1 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et 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/assert.h"
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#include "libc/atomic.h"
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#include "libc/calls/struct/rlimit.h"
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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/calls/struct/ucontext.internal.h"
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#include "libc/calls/ucontext.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.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/stdio/rand.h"
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#include "libc/stdio/stdio.h"
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#include "libc/stdio/sysparam.h"
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#include "libc/sysv/consts/map.h"
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#include "libc/sysv/consts/prot.h"
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#include "libc/sysv/consts/rlimit.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/thread/thread.h"
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/**
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* stack overflow recovery technique #1
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* overflow the gigantic main process stack
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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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atomic_bool g_isdone;
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atomic_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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unassert(!sigaltstack(0, &ss));
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unassert(SS_ONSTACK == ss.ss_flags);
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kprintf("kprintf avoids overflowing %G si_addr=%lx sp=%lx\n", si->si_signo,
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si->si_addr, ((ucontext_t *)ctx)->uc_mcontext.SP);
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smashed_stack = true;
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unassert(__is_stack_overflow(si, ctx));
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longjmp(recover, 123);
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}
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void SetUp(void) {
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// tune down the main process's stack size to a reasonable amount
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// some operating systems, e.g. freebsd, will do things like have
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// 500mb RLIMIT_STACK by default, even on machines with 400mb RAM
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if (!IsWindows() && !IsXnu()) {
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struct rlimit rl;
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getrlimit(RLIMIT_STACK, &rl);
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rl.rlim_cur = MIN(rl.rlim_cur, 2 * 1024 * 1024);
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unassert(!setrlimit(RLIMIT_STACK, &rl));
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}
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// set up the signal handler and alternative stack
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struct sigaction sa;
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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) + 8192;
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ss.ss_sp = _mapanon(ss.ss_size);
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unassert(!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, 0);
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sigaction(SIGSEGV, &sa, 0);
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}
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int StackOverflow(int d) {
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char A[8];
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for (int i = 0; i < sizeof(A); i++)
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A[i] = d + i;
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if (__veil("r", d))
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return StackOverflow(d + 1) + A[d % sizeof(A)];
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return 0;
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}
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void *innocent_thread(void *arg) {
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atomic_long dont_clobber_me_bro = 0;
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while (!g_isdone)
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unassert(!dont_clobber_me_bro);
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return 0;
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}
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int main() {
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// libc/intrin/stack.c is designed so that this thread's stack should
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// be allocated right beneath the main thread's stack. our goal is to
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// make sure overflowing the main stack won't clobber our poor thread
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pthread_t th;
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unassert(!pthread_create(&th, 0, innocent_thread, 0));
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SetUp();
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int jumpcode;
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if (!(jumpcode = setjmp(recover)))
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exit(StackOverflow(1));
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unassert(123 == jumpcode);
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unassert(smashed_stack);
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// join the thread
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g_isdone = true;
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unassert(!pthread_join(th, 0));
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// here's where longjmp() gets us into trouble
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struct sigaltstack ss;
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unassert(!sigaltstack(0, &ss));
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if (IsXnu() || IsNetbsd()) {
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unassert(SS_ONSTACK == ss.ss_flags); // wut
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} else {
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unassert(0 == ss.ss_flags);
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}
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}
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