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i#1921 native sig: Account for sigaltstack when placing native frames #4645

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Dec 31, 2020
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i#1921 native sig: Account for sigaltstack when placing native frames #4645

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107 changes: 61 additions & 46 deletions core/unix/signal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -443,6 +443,21 @@ handler_alloc(dcontext_t *dcontext, size_t size)
return global_heap_alloc(size HEAPACCT(ACCT_OTHER));
}

/* Does not return. */
static void
report_unhandleable_signal_and_exit(int sig, const char *sub_message)
{
/* TODO i#1921: Add more info such as the PC and disasm of surrounding instrs. */
char signum_str[8];
snprintf(signum_str, BUFFER_SIZE_ELEMENTS(signum_str), "%d", sig);
NULL_TERMINATE_BUFFER(signum_str);
char tid_str[16];
snprintf(tid_str, BUFFER_SIZE_ELEMENTS(tid_str), TIDFMT, get_sys_thread_id());
NULL_TERMINATE_BUFFER(tid_str);
REPORT_FATAL_ERROR_AND_EXIT(FAILED_TO_HANDLE_SIGNAL, 5, get_application_name(),
get_application_pid(), signum_str, tid_str, sub_message);
}

/**** top-level routines ***********************************************/

static bool
Expand Down Expand Up @@ -2957,11 +2972,39 @@ get_sigstack_frame_ptr(dcontext_t *dcontext, thread_sig_info_t *info, int sig,
if (frame != NULL) {
/* Signal happened natively or while in the cache: grab interrupted xsp. */
sp = (byte *)sc->SC_XSP;
LOG(THREAD, LOG_ASYNCH, 3, "get_sigstack_frame_ptr: using frame's xsp " PFX "\n",
sp);
} else {
/* signal happened while in DR, use stored xsp */
sp = (byte *)get_mcontext(dcontext)->xsp;
LOG(THREAD, LOG_ASYNCH, 3, "get_sigstack_frame_ptr: using app xsp " PFX "\n", sp);
}

if (USE_APP_SIGSTACK(info, sig)) {
/* app has own signal stack which is enabled for this handler */
LOG(THREAD, LOG_ASYNCH, 3, "get_sigstack_frame_ptr: app has own stack " PFX "\n",
info->app_sigstack.ss_sp);
LOG(THREAD, LOG_ASYNCH, 3, "\tcur sp=" PFX " vs app stack " PFX "-" PFX "\n", sp,
info->app_sigstack.ss_sp,
info->app_sigstack.ss_sp + info->app_sigstack.ss_size);
if (sp > (byte *)info->app_sigstack.ss_sp &&
sp - (byte *)info->app_sigstack.ss_sp < info->app_sigstack.ss_size) {
/* we're currently in the alt stack, so use current xsp */
LOG(THREAD, LOG_ASYNCH, 3,
"\tinside alt stack, so using current xsp " PFX "\n", sp);
} else {
/* need to go to top, stack grows down */
sp = info->app_sigstack.ss_sp + info->app_sigstack.ss_size;
LOG(THREAD, LOG_ASYNCH, 3,
"\tnot inside alt stack, so using base xsp " PFX "\n", sp);
}
}

if (frame != NULL) {
/* Handle DR's frame already being on the app stack. For native delivery we
* could try to re-use this frame, but that doesn't work with plain vs rt.
* Instead we move below and live with the downsides of a potential stack
* overflow and confusing the app over why it's so low: but this is an app
* with no sigaltstack so it should have plenty of room.
* overflow.
*/
size_t frame_sz_max = sizeof(sigframe_rt_t) + REDZONE_SIZE +
IF_LINUX(IF_X86((sc->fpstate == NULL ? 0
Expand All @@ -2975,43 +3018,30 @@ get_sigstack_frame_ptr(dcontext_t *dcontext, thread_sig_info_t *info, int sig,
/* We have to copy the frame below our own stack usage high watermark
* in the rest of the code we'll execute from execute_native_handler().
* Kind of a mess. For now we estimate two pages which should be plenty
* and still not be egregious usage for most app stacks.
* and still not be egregious usage for most app stacks. For the altstack
* we check the size below.
*/
#define EXECUTE_NATIVE_STACK_USAGE (4096 * 2)
if (sp > cur_sp && sp - frame_sz_max - EXECUTE_NATIVE_STACK_USAGE < cur_sp) {
sp = cur_sp - frame_sz_max - EXECUTE_NATIVE_STACK_USAGE;
}
if (USE_APP_SIGSTACK(info, sig)) {
#define APP_ALTSTACK_USAGE (SIGSTKSZ / 2)
if (sp - APP_ALTSTACK_USAGE < (byte *)info->app_sigstack.ss_sp) {
/* There's not enough stack space. The only solution would be to
* re-use DR's frame and limit our own stack usage here, which
* gets complex. We bail.
*/
report_unhandleable_signal_and_exit(
sig, "sigaltstack too small in native thread");
ASSERT_NOT_REACHED();
}
}
LOG(THREAD, LOG_ASYNCH, 3,
"get_sigstack_frame_ptr: moving beyond same-stack frame to %p\n", sp);
} else {
LOG(THREAD, LOG_ASYNCH, 3,
"get_sigstack_frame_ptr: using frame's xsp " PFX "\n", sp);
}
} else {
/* signal happened while in DR, use stored xsp */
sp = (byte *)get_mcontext(dcontext)->xsp;
LOG(THREAD, LOG_ASYNCH, 3, "get_sigstack_frame_ptr: using app xsp " PFX "\n", sp);
}

if (USE_APP_SIGSTACK(info, sig)) {
/* app has own signal stack which is enabled for this handler */
LOG(THREAD, LOG_ASYNCH, 3, "get_sigstack_frame_ptr: app has own stack " PFX "\n",
info->app_sigstack.ss_sp);
LOG(THREAD, LOG_ASYNCH, 3, "\tcur sp=" PFX " vs app stack " PFX "-" PFX "\n", sp,
info->app_sigstack.ss_sp,
info->app_sigstack.ss_sp + info->app_sigstack.ss_size);
if (sp > (byte *)info->app_sigstack.ss_sp &&
sp - (byte *)info->app_sigstack.ss_sp < info->app_sigstack.ss_size) {
/* we're currently in the alt stack, so use current xsp */
LOG(THREAD, LOG_ASYNCH, 3,
"\tinside alt stack, so using current xsp " PFX "\n", sp);
} else {
/* need to go to top, stack grows down */
sp = info->app_sigstack.ss_sp + info->app_sigstack.ss_size;
LOG(THREAD, LOG_ASYNCH, 3,
"\tnot inside alt stack, so using base xsp " PFX "\n", sp);
}
}
/* now get frame pointer: need to go down to first field of frame */
sp -= get_app_frame_size(info, sig);
#if defined(LINUX) && defined(X86)
Expand Down Expand Up @@ -5814,21 +5844,6 @@ execute_handler_from_dispatch(dcontext_t *dcontext, int sig)
return true;
}

/* Does not return. */
static void
report_unhandleable_signal_and_exit(int sig)
{
/* TODO i#1921: Add more info such as the PC and disasm of surrounding instrs. */
char signum_str[8];
snprintf(signum_str, BUFFER_SIZE_ELEMENTS(signum_str), "%d", sig);
NULL_TERMINATE_BUFFER(signum_str);
char tid_str[16];
snprintf(tid_str, BUFFER_SIZE_ELEMENTS(tid_str), TIDFMT, get_sys_thread_id());
NULL_TERMINATE_BUFFER(tid_str);
REPORT_FATAL_ERROR_AND_EXIT(FAILED_TO_HANDLE_SIGNAL, 4, get_application_name(),
get_application_pid(), signum_str, tid_str);
}

/* Sends a signal to a currently-native thread. dcontext can be NULL. */
static void
execute_native_handler(dcontext_t *dcontext, int sig, sigframe_rt_t *our_frame)
Expand All @@ -5848,7 +5863,7 @@ execute_native_handler(dcontext_t *dcontext, int sig, sigframe_rt_t *our_frame)
} else {
if (atomic_read_bool(&multiple_handlers_present)) {
/* See i#1921 comment up top: we don't handle this. */
report_unhandleable_signal_and_exit(sig);
report_unhandleable_signal_and_exit(sig, "multiple native handlers");
ASSERT_NOT_REACHED();
}
info = &synthetic;
Expand Down Expand Up @@ -5909,7 +5924,7 @@ execute_native_handler(dcontext_t *dcontext, int sig, sigframe_rt_t *our_frame)
}
if (default_action[sig] == DEFAULT_IGNORE)
return;
report_unhandleable_signal_and_exit(sig);
report_unhandleable_signal_and_exit(sig, "default action in native thread");
ASSERT_NOT_REACHED();
return;
}
Expand Down
2 changes: 1 addition & 1 deletion core/win32/events.mc
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Original file line number Diff line number Diff line change
Expand Up @@ -632,7 +632,7 @@ Severity = Error
Facility = DRCore
SymbolicName = MSG_FAILED_TO_HANDLE_SIGNAL
Language=English
Application %1!s! (%2!s!). Cannot correctly handle received signal %3!s! in thread %4!s!.
Application %1!s! (%2!s!). Cannot correctly handle received signal %3!s! in thread %4!s!: %5!s!.
.
;#endif

Expand Down
28 changes: 24 additions & 4 deletions suite/tests/api/detach_signal.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,9 @@
# define VPRINT(...) /* nothing */
#endif

/* SIGSTKSZ*2 results in a fatal error from DR on fitting the copied frame. */
#define ALT_STACK_SIZE (SIGSTKSZ * 4)

static volatile bool sideline_exit = false;
static void *sideline_continue;
static void *sideline_ready[NUM_THREADS];
Expand Down Expand Up @@ -103,14 +106,21 @@ sideline_spinner(void *arg)
VPRINT("%d signaling sideline_ready\n", idx);
signal_cond_var(sideline_ready[idx]);

stack_t sigstack;
sigstack.ss_sp = (char *)malloc(ALT_STACK_SIZE);
sigstack.ss_size = ALT_STACK_SIZE;
sigstack.ss_flags = 0;
int res = sigaltstack(&sigstack, NULL);
assert(res == 0);

/* Block some signals to test mask preservation. */
sigset_t mask = {
0, /* Set padding to 0 so we can use memcmp */
};
sigemptyset(&mask);
sigaddset(&mask, SIGUSR1);
sigaddset(&mask, SIGURG);
int res = sigprocmask(SIG_SETMASK, &mask, NULL);
res = sigprocmask(SIG_SETMASK, &mask, NULL);
assert(res == 0);

/* Now sit in a signal-generating loop. */
Expand All @@ -135,6 +145,16 @@ sideline_spinner(void *arg)
assert(res == 0 && memcmp(&mask, &check_mask, sizeof(mask)) == 0);
}

stack_t check_stack;
res = sigaltstack(NULL, &check_stack);
assert(res == 0 && check_stack.ss_sp == sigstack.ss_sp &&
check_stack.ss_size == sigstack.ss_size &&
check_stack.ss_flags == sigstack.ss_flags);
sigstack.ss_flags = SS_DISABLE;
res = sigaltstack(&sigstack, NULL);
assert(res == 0);
free(sigstack.ss_sp);

return THREAD_FUNC_RETURN_ZERO;
}

Expand Down Expand Up @@ -166,10 +186,10 @@ main(void)
res = sigprocmask(SIG_SETMASK, &prior_mask, NULL);
assert(res == 0);

intercept_signal_with_mask(SIGSEGV, (handler_3_t)&handle_signal, false,
&handler_mask);
/* We request an alt stack for some signals but not all to test both types. */
intercept_signal_with_mask(SIGSEGV, (handler_3_t)&handle_signal, true, &handler_mask);
intercept_signal_with_mask(SIGBUS, (handler_3_t)&handle_signal, false, &handler_mask);
intercept_signal_with_mask(SIGURG, (handler_3_t)&handle_signal, false, &handler_mask);
intercept_signal_with_mask(SIGURG, (handler_3_t)&handle_signal, true, &handler_mask);
intercept_signal_with_mask(SIGALRM, (handler_3_t)&handle_signal, false,
&handler_mask);

Expand Down