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Improve stack overflow recovery

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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.
This commit is contained in:
Justine Tunney 2023-10-04 07:07:43 -07:00
parent 1694edf85c
commit 4631d34d0d
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24 changed files with 590 additions and 274 deletions
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test/libc/thread/stackoverflow2_test.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2023 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/struct/sigaction.h"
#include "libc/calls/struct/sigaltstack.h"
#include "libc/calls/struct/siginfo.h"
#include "libc/dce.h"
#include "libc/intrin/kprintf.h"
#include "libc/limits.h"
#include "libc/mem/gc.internal.h"
#include "libc/mem/mem.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/sysconf.h"
#include "libc/sysv/consts/sa.h"
#include "libc/sysv/consts/sig.h"
#include "libc/sysv/consts/ss.h"
#include "libc/testlib/testlib.h"
#include "libc/thread/thread.h"
/**
* stack overflow recovery technique #2
* longjmp out of signal back into thread
* simple but it can upset kernels / libraries
*/
jmp_buf recover;
volatile bool smashed_stack;
void CrashHandler(int sig, siginfo_t *si, void *ctx) {
struct sigaltstack ss;
ASSERT_SYS(0, 0, sigaltstack(0, &ss));
ASSERT_EQ(SS_ONSTACK, ss.ss_flags);
kprintf("kprintf avoids overflowing %G %p\n", si->si_signo, si->si_addr);
smashed_stack = true;
ASSERT_TRUE(__is_stack_overflow(si, ctx));
longjmp(recover, 123);
}
int StackOverflow(int f(), int n) {
if (n < INT_MAX) {
return f(f, n + 1) - 1;
} else {
return INT_MAX;
}
}
int (*pStackOverflow)(int (*)(), int) = StackOverflow;
void *MyPosixThread(void *arg) {
int jumpcode;
struct sigaction sa, o1, o2;
struct sigaltstack ss;
ss.ss_flags = 0;
ss.ss_size = sysconf(_SC_MINSIGSTKSZ) + 4096;
ss.ss_sp = gc(malloc(ss.ss_size));
ASSERT_SYS(0, 0, sigaltstack(&ss, 0));
sa.sa_flags = SA_SIGINFO | SA_ONSTACK; // <-- important
sigemptyset(&sa.sa_mask);
sa.sa_sigaction = CrashHandler;
sigaction(SIGBUS, &sa, &o1);
sigaction(SIGSEGV, &sa, &o2);
if (!(jumpcode = setjmp(recover))) {
exit(pStackOverflow(pStackOverflow, 0));
}
ASSERT_EQ(123, jumpcode);
sigaction(SIGSEGV, &o2, 0);
sigaction(SIGBUS, &o1, 0);
// here's where longjmp() gets us into trouble
ASSERT_SYS(0, 0, sigaltstack(0, &ss));
if (IsXnu() || IsNetbsd()) {
ASSERT_EQ(SS_ONSTACK, ss.ss_flags); // wut
} else {
ASSERT_EQ(0, ss.ss_flags);
}
return 0;
}
TEST(stackoverflow, standardStack_altStack_thread_longjmp) {
pthread_t th;
struct sigaltstack ss;
for (int i = 0; i < 2; ++i) {
smashed_stack = false;
pthread_create(&th, 0, MyPosixThread, 0);
pthread_join(th, 0);
ASSERT_TRUE(smashed_stack);
// this should be SS_DISABLE but ShowCrashReports() creates an alt stack
ASSERT_SYS(0, 0, sigaltstack(0, &ss));
ASSERT_EQ(0, ss.ss_flags);
}
}