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GH-139653: Only raise an exception (or fatal error) when the stack pointer is about to overflow the stack. (GH-141711)

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Only raises if the stack pointer is both below the limit *and* above the stack base.
This prevents false positives for user-space threads, as the stack pointer will be outside those bounds
if the stack has been swapped.
This commit is contained in:
Mark Shannon 2025-11-19 10:16:24 +00:00 • committed by GitHub
parent 5d1f8f2d03
commit c25a070759
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4 changed files with 38 additions and 10 deletions
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28
Python/ceval.c
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@ -362,9 +362,11 @@ _Py_ReachedRecursionLimitWithMargin(PyThreadState *tstate, int margin_count)
_Py_InitializeRecursionLimits(tstate);
}
#if _Py_STACK_GROWS_DOWN
return here_addr <= _tstate->c_stack_soft_limit + margin_count * _PyOS_STACK_MARGIN_BYTES;
return here_addr <= _tstate->c_stack_soft_limit + margin_count * _PyOS_STACK_MARGIN_BYTES &&
here_addr >= _tstate->c_stack_soft_limit - 2 * _PyOS_STACK_MARGIN_BYTES;
#else
return here_addr > _tstate->c_stack_soft_limit - margin_count * _PyOS_STACK_MARGIN_BYTES;
return here_addr > _tstate->c_stack_soft_limit - margin_count * _PyOS_STACK_MARGIN_BYTES &&
here_addr <= _tstate->c_stack_soft_limit + 2 * _PyOS_STACK_MARGIN_BYTES;
#endif
}
@ -455,7 +457,7 @@ int pthread_attr_destroy(pthread_attr_t *a)
#endif
static void
hardware_stack_limits(uintptr_t *base, uintptr_t *top)
hardware_stack_limits(uintptr_t *base, uintptr_t *top, uintptr_t sp)
{
#ifdef WIN32
ULONG_PTR low, high;
@ -491,10 +493,19 @@ hardware_stack_limits(uintptr_t *base, uintptr_t *top)
return;
}
# endif
uintptr_t here_addr = _Py_get_machine_stack_pointer();
uintptr_t top_addr = _Py_SIZE_ROUND_UP(here_addr, 4096);
// Add some space for caller function then round to minimum page size
// This is a guess at the top of the stack, but should be a reasonably
// good guess if called from _PyThreadState_Attach when creating a thread.
// If the thread is attached deep in a call stack, then the guess will be poor.
#if _Py_STACK_GROWS_DOWN
uintptr_t top_addr = _Py_SIZE_ROUND_UP(sp + 8*sizeof(void*), SYSTEM_PAGE_SIZE);
*top = top_addr;
*base = top_addr - Py_C_STACK_SIZE;
# else
uintptr_t base_addr = _Py_SIZE_ROUND_DOWN(sp - 8*sizeof(void*), SYSTEM_PAGE_SIZE);
*base = base_addr;
*top = base_addr + Py_C_STACK_SIZE;
#endif
#endif
}
@ -543,7 +554,8 @@ void
_Py_InitializeRecursionLimits(PyThreadState *tstate)
{
uintptr_t base, top;
hardware_stack_limits(&base, &top);
uintptr_t here_addr = _Py_get_machine_stack_pointer();
hardware_stack_limits(&base, &top, here_addr);
assert(top != 0);
tstate_set_stack(tstate, base, top);
@ -587,7 +599,7 @@ PyUnstable_ThreadState_ResetStackProtection(PyThreadState *tstate)
/* The function _Py_EnterRecursiveCallTstate() only calls _Py_CheckRecursiveCall()
if the recursion_depth reaches recursion_limit. */
if the stack pointer is between the stack base and c_stack_hard_limit. */
int
_Py_CheckRecursiveCall(PyThreadState *tstate, const char *where)
{
@ -596,10 +608,12 @@ _Py_CheckRecursiveCall(PyThreadState *tstate, const char *where)
assert(_tstate->c_stack_soft_limit != 0);
assert(_tstate->c_stack_hard_limit != 0);
#if _Py_STACK_GROWS_DOWN
assert(here_addr >= _tstate->c_stack_hard_limit - _PyOS_STACK_MARGIN_BYTES);
if (here_addr < _tstate->c_stack_hard_limit) {
/* Overflowing while handling an overflow. Give up. */
int kbytes_used = (int)(_tstate->c_stack_top - here_addr)/1024;
#else
assert(here_addr <= _tstate->c_stack_hard_limit + _PyOS_STACK_MARGIN_BYTES);
if (here_addr > _tstate->c_stack_hard_limit) {
/* Overflowing while handling an overflow. Give up. */
int kbytes_used = (int)(here_addr - _tstate->c_stack_top)/1024;