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py/objexcept: Prevent infinite recursion when allocating exceptions. 

The aim of this patch is to rewrite the functions that create exception
instances (mp_obj_exception_make_new and mp_obj_new_exception_msg_varg) so
that they do not call any functions that may raise an exception.  Otherwise
it's possible to create infinite recursion with an exception being raised
while trying to create an exception object.

The two main things that are done to accomplish this are:
1. Change mp_obj_new_exception_msg_varg to just format the string, then
   call mp_obj_exception_make_new to actually create the exception object.
2. In mp_obj_exception_make_new and mp_obj_new_exception_msg_varg try to
   allocate all memory first using functions that don't raise exceptions
   If any of the memory allocations fail (return NULL) then degrade
   gracefully by trying other options for memory allocation, eg using the
   emergency exception buffer.
3. Use a custom printer backend to conservatively format strings: if it
   can't allocate memory then it just truncates the string.

As part of this rewrite, raising an exception without a message, like
KeyError(123), will now use the emergency buffer to store the arg and
traceback data if there is no heap memory available.

Memory use with this patch is unchanged.  Code size is increased by:

   bare-arm:  +136
minimal x86:  +124
   unix x64:   +72
unix nanbox:   +96
      stm32:   +88
    esp8266:   +92
     cc3200:   +80
This commit is contained in:
Damien George 2017-09-21 15:24:57 +10:00
parent 347de3e218
commit 96fd80db13
4 changed files with 181 additions and 94 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

241
py/objexcept.c
View File

@ -38,6 +38,12 @@
#include "py/gc.h"
#include "py/mperrno.h"
// Number of items per traceback entry (file, line, block)
#define TRACEBACK_ENTRY_LEN (3)
// Number of traceback entries to reserve in the emergency exception buffer
#define EMG_TRACEBACK_ALLOC (2 * TRACEBACK_ENTRY_LEN)
// Instance of MemoryError exception - needed by mp_malloc_fail
const mp_obj_exception_t mp_const_MemoryError_obj = {{&mp_type_MemoryError}, 0, 0, NULL, (mp_obj_tuple_t*)&mp_const_empty_tuple_obj};
@ -127,18 +133,51 @@ STATIC void mp_obj_exception_print(const mp_print_t *print, mp_obj_t o_in, mp_pr
mp_obj_t mp_obj_exception_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
mp_arg_check_num(n_args, n_kw, 0, MP_OBJ_FUN_ARGS_MAX, false);
mp_obj_exception_t *o = m_new_obj_var_maybe(mp_obj_exception_t, mp_obj_t, 0);
if (o == NULL) {
// Couldn't allocate heap memory; use local data instead.
o = &MP_STATE_VM(mp_emergency_exception_obj);
// We can't store any args.
o->args = (mp_obj_tuple_t*)&mp_const_empty_tuple_obj;
} else {
o->args = MP_OBJ_TO_PTR(mp_obj_new_tuple(n_args, args));
// Try to allocate memory for the exception, with fallback to emergency exception object
mp_obj_exception_t *o_exc = m_new_obj_maybe(mp_obj_exception_t);
if (o_exc == NULL) {
o_exc = &MP_STATE_VM(mp_emergency_exception_obj);
}
o->base.type = type;
o->traceback_data = NULL;
return MP_OBJ_FROM_PTR(o);
// Populate the exception object
o_exc->base.type = type;
o_exc->traceback_data = NULL;
mp_obj_tuple_t *o_tuple;
if (n_args == 0) {
// No args, can use the empty tuple straightaway
o_tuple = (mp_obj_tuple_t*)&mp_const_empty_tuple_obj;
} else {
// Try to allocate memory for the tuple containing the args
o_tuple = m_new_obj_var_maybe(mp_obj_tuple_t, mp_obj_t, n_args);
#if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
// If we are called by mp_obj_new_exception_msg_varg then it will have
// reserved room (after the traceback data) for a tuple with 1 element.
// Otherwise we are free to use the whole buffer after the traceback data.
if (o_tuple == NULL && mp_emergency_exception_buf_size >=
EMG_TRACEBACK_ALLOC * sizeof(size_t) + sizeof(mp_obj_tuple_t) + n_args * sizeof(mp_obj_t)) {
o_tuple = (mp_obj_tuple_t*)
((uint8_t*)MP_STATE_VM(mp_emergency_exception_buf) + EMG_TRACEBACK_ALLOC * sizeof(size_t));
}
#endif
if (o_tuple == NULL) {
// No memory for a tuple, fallback to an empty tuple
o_tuple = (mp_obj_tuple_t*)&mp_const_empty_tuple_obj;
} else {
// Have memory for a tuple so populate it
o_tuple->base.type = &mp_type_tuple;
o_tuple->len = n_args;
memcpy(o_tuple->items, args, n_args * sizeof(mp_obj_t));
}
}
// Store the tuple of args in the exception object
o_exc->args = o_tuple;
return MP_OBJ_FROM_PTR(o_exc);
}
// Get exception "value" - that is, first argument, or None
@ -306,87 +345,95 @@ mp_obj_t mp_obj_new_exception_msg(const mp_obj_type_t *exc_type, const char *msg
return mp_obj_new_exception_msg_varg(exc_type, msg);
}
// The following struct and function implement a simple printer that conservatively
// allocates memory and truncates the output data if no more memory can be obtained.
// It leaves room for a null byte at the end of the buffer.
struct _exc_printer_t {
bool allow_realloc;
size_t alloc;
size_t len;
byte *buf;
};
STATIC void exc_add_strn(void *data, const char *str, size_t len) {
struct _exc_printer_t *pr = data;
if (pr->len + len >= pr->alloc) {
// Not enough room for data plus a null byte so try to grow the buffer
if (pr->allow_realloc) {
size_t new_alloc = pr->alloc + len + 16;
byte *new_buf = m_renew_maybe(byte, pr->buf, pr->alloc, new_alloc, true);
if (new_buf == NULL) {
pr->allow_realloc = false;
len = pr->alloc - pr->len - 1;
} else {
pr->alloc = new_alloc;
pr->buf = new_buf;
}
} else {
len = pr->alloc - pr->len - 1;
}
}
memcpy(pr->buf + pr->len, str, len);
pr->len += len;
}
mp_obj_t mp_obj_new_exception_msg_varg(const mp_obj_type_t *exc_type, const char *fmt, ...) {
// check that the given type is an exception type
assert(fmt != NULL);
// Check that the given type is an exception type
assert(exc_type->make_new == mp_obj_exception_make_new);
// make exception object
mp_obj_exception_t *o = m_new_obj_var_maybe(mp_obj_exception_t, mp_obj_t, 0);
if (o == NULL) {
// Couldn't allocate heap memory; use local data instead.
// Unfortunately, we won't be able to format the string...
o = &MP_STATE_VM(mp_emergency_exception_obj);
o->base.type = exc_type;
o->traceback_data = NULL;
o->args = (mp_obj_tuple_t*)&mp_const_empty_tuple_obj;
// Try to allocate memory for the message
mp_obj_str_t *o_str = m_new_obj_maybe(mp_obj_str_t);
size_t o_str_alloc = strlen(fmt) + 1;
byte *o_str_buf = m_new_maybe(byte, o_str_alloc);
bool used_emg_buf = false;
#if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
// If the user has provided a buffer, then we try to create a tuple
// of length 1, which has a string object and the string data.
// If memory allocation failed and there is an emergency buffer then try to use
// that buffer to store the string object and its data (at least 16 bytes for
// the string data), reserving room at the start for the traceback and 1-tuple.
if ((o_str == NULL || o_str_buf == NULL)
&& mp_emergency_exception_buf_size >= EMG_TRACEBACK_ALLOC * sizeof(size_t)
+ sizeof(mp_obj_tuple_t) + sizeof(mp_obj_t) + sizeof(mp_obj_str_t) + 16) {
used_emg_buf = true;
o_str = (mp_obj_str_t*)((uint8_t*)MP_STATE_VM(mp_emergency_exception_buf)
+ EMG_TRACEBACK_ALLOC * sizeof(size_t) + sizeof(mp_obj_tuple_t) + sizeof(mp_obj_t));
o_str_buf = (byte*)&o_str[1];
o_str_alloc = (uint8_t*)MP_STATE_VM(mp_emergency_exception_buf)
+ mp_emergency_exception_buf_size - o_str_buf;
}
#endif
if (mp_emergency_exception_buf_size > (sizeof(mp_obj_tuple_t) + sizeof(mp_obj_str_t) + sizeof(mp_obj_t))) {
mp_obj_tuple_t *tuple = (mp_obj_tuple_t *)MP_STATE_VM(mp_emergency_exception_buf);
mp_obj_str_t *str = (mp_obj_str_t *)&tuple->items[1];
tuple->base.type = &mp_type_tuple;
tuple->len = 1;
tuple->items[0] = MP_OBJ_FROM_PTR(str);
byte *str_data = (byte *)&str[1];
size_t max_len = (byte*)MP_STATE_VM(mp_emergency_exception_buf) + mp_emergency_exception_buf_size
- str_data;
vstr_t vstr;
vstr_init_fixed_buf(&vstr, max_len, (char *)str_data);
if (o_str == NULL) {
// No memory for the string object so create the exception with no args
return mp_obj_exception_make_new(exc_type, 0, 0, NULL);
}
if (o_str_buf == NULL) {
// No memory for the string buffer: assume that the fmt string is in ROM
// and use that data as the data of the string
o_str->len = o_str_alloc - 1; // will be equal to strlen(fmt)
o_str->data = (const byte*)fmt;
} else {
// We have some memory to format the string
struct _exc_printer_t exc_pr = {!used_emg_buf, o_str_alloc, 0, o_str_buf};
mp_print_t print = {&exc_pr, exc_add_strn};
va_list ap;
va_start(ap, fmt);
vstr_vprintf(&vstr, fmt, ap);
mp_vprintf(&print, fmt, ap);
va_end(ap);
str->base.type = &mp_type_str;
str->hash = qstr_compute_hash(str_data, str->len);
str->len = vstr.len;
str->data = str_data;
o->args = tuple;
size_t offset = &str_data[str->len] - (byte*)MP_STATE_VM(mp_emergency_exception_buf);
offset += sizeof(void *) - 1;
offset &= ~(sizeof(void *) - 1);
if ((mp_emergency_exception_buf_size - offset) > (sizeof(o->traceback_data[0]) * 3)) {
// We have room to store some traceback.
o->traceback_data = (size_t*)((byte *)MP_STATE_VM(mp_emergency_exception_buf) + offset);
o->traceback_alloc = ((byte*)MP_STATE_VM(mp_emergency_exception_buf) + mp_emergency_exception_buf_size - (byte *)o->traceback_data) / sizeof(o->traceback_data[0]);
o->traceback_len = 0;
}
}
#endif // MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
} else {
o->base.type = exc_type;
o->traceback_data = NULL;
o->args = MP_OBJ_TO_PTR(mp_obj_new_tuple(1, NULL));
assert(fmt != NULL);
{
if (strchr(fmt, '%') == NULL) {
// no formatting substitutions, avoid allocating vstr.
o->args->items[0] = mp_obj_new_str(fmt, strlen(fmt), false);
} else {
// render exception message and store as .args[0]
va_list ap;
vstr_t vstr;
vstr_init(&vstr, 16);
va_start(ap, fmt);
vstr_vprintf(&vstr, fmt, ap);
va_end(ap);
o->args->items[0] = mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
}
}
exc_pr.buf[exc_pr.len] = '\0';
o_str->len = exc_pr.len;
o_str->data = exc_pr.buf;
}
return MP_OBJ_FROM_PTR(o);
// Create the string object and call mp_obj_exception_make_new to create the exception
o_str->base.type = &mp_type_str;
o_str->hash = qstr_compute_hash(o_str->data, o_str->len);
mp_obj_t arg = MP_OBJ_FROM_PTR(o_str);
return mp_obj_exception_make_new(exc_type, 1, 0, &arg);
}
// return true if the given object is an exception type
@ -443,24 +490,46 @@ void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, size_t line, qs
// if memory allocation fails (eg because gc is locked), just return
if (self->traceback_data == NULL) {
self->traceback_data = m_new_maybe(size_t, 3);
self->traceback_data = m_new_maybe(size_t, TRACEBACK_ENTRY_LEN);
if (self->traceback_data == NULL) {
#if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
if (mp_emergency_exception_buf_size >= EMG_TRACEBACK_ALLOC * sizeof(size_t)) {
// There is room in the emergency buffer for traceback data
size_t *tb = (size_t*)MP_STATE_VM(mp_emergency_exception_buf);
self->traceback_data = tb;
self->traceback_alloc = EMG_TRACEBACK_ALLOC;
} else {
// Can't allocate and no room in emergency buffer
return;
}
self->traceback_alloc = 3;
#else
// Can't allocate
return;
#endif
} else {
// Allocated the traceback data on the heap
self->traceback_alloc = TRACEBACK_ENTRY_LEN;
}
self->traceback_len = 0;
} else if (self->traceback_len + 3 > self->traceback_alloc) {
} else if (self->traceback_len + TRACEBACK_ENTRY_LEN > self->traceback_alloc) {
#if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
if (self->traceback_data == (size_t*)MP_STATE_VM(mp_emergency_exception_buf)) {
// Can't resize the emergency buffer
return;
}
#endif
// be conservative with growing traceback data
size_t *tb_data = m_renew_maybe(size_t, self->traceback_data, self->traceback_alloc, self->traceback_alloc + 3, true);
size_t *tb_data = m_renew_maybe(size_t, self->traceback_data, self->traceback_alloc,
self->traceback_alloc + TRACEBACK_ENTRY_LEN, true);
if (tb_data == NULL) {
return;
}
self->traceback_data = tb_data;
self->traceback_alloc += 3;
self->traceback_alloc += TRACEBACK_ENTRY_LEN;
}
size_t *tb_data = &self->traceback_data[self->traceback_len];
self->traceback_len += 3;
self->traceback_len += TRACEBACK_ENTRY_LEN;
tb_data[0] = file;
tb_data[1] = line;
tb_data[2] = block;

16
tests/micropython/emg_exc.py
View File

@ -2,6 +2,11 @@
import micropython
import sys
try:
import uio
except ImportError:
print("SKIP")
raise SystemExit
# some ports need to allocate heap for the emg exc
try:
@ -14,7 +19,16 @@ def f():
try:
raise ValueError(1)
except ValueError as er:
sys.print_exception(er)
exc = er
micropython.heap_unlock()
# print the exception
buf = uio.StringIO()
sys.print_exception(exc, buf)
for l in buf.getvalue().split("\n"):
if l.startswith(" File "):
print(l.split('"')[2])
else:
print(l)
f()

5
tests/micropython/emg_exc.py.exp
View File

@ -1 +1,4 @@
ValueError:
Traceback (most recent call last):
, line 20, in f
ValueError: 1

1
tests/run-tests
View File

@ -345,6 +345,7 @@ def run_tests(pyb, tests, args, base_path="."):
skip_tests.add('misc/rge_sm.py') # requires yield
skip_tests.add('misc/print_exception.py') # because native doesn't have proper traceback info
skip_tests.add('misc/sys_exc_info.py') # sys.exc_info() is not supported for native
skip_tests.add('micropython/emg_exc.py') # because native doesn't have proper traceback info
skip_tests.add('micropython/heapalloc_traceback.py') # because native doesn't have proper traceback info
skip_tests.add('micropython/heapalloc_iter.py') # requires generators
skip_tests.add('micropython/schedule.py') # native code doesn't check pending events