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/* $OpenBSD: rthread_stack.c,v 1.20 2021/09/17 15:20:21 deraadt Exp $ */
/* PUBLIC DOMAIN: No Rights Reserved. Marco S Hyman <marc@snafu.org> */
#include <sys/types.h>
#include <sys/mman.h>
#include <errno.h>
#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include "rthread.h"
/*
* Follow uthread's example and keep around stacks that have default
* attributes for possible reuse.
*/
static SLIST_HEAD(, stack) def_stacks = SLIST_HEAD_INITIALIZER(head);
static _atomic_lock_t def_stacks_lock = _SPINLOCK_UNLOCKED;
struct stack *
_rthread_alloc_stack(pthread_t thread)
{
struct stack *stack;
u_int32_t rnd;
caddr_t base;
caddr_t guard;
size_t size;
size_t guardsize;
/* if the request uses the defaults, try to reuse one */
if (thread->attr.stack_addr == NULL &&
thread->attr.stack_size == RTHREAD_STACK_SIZE_DEF &&
thread->attr.guard_size == _thread_pagesize) {
_spinlock(&def_stacks_lock);
stack = SLIST_FIRST(&def_stacks);
if (stack != NULL) {
SLIST_REMOVE_HEAD(&def_stacks, link);
_spinunlock(&def_stacks_lock);
return (stack);
}
_spinunlock(&def_stacks_lock);
}
/* allocate the stack struct that we'll return */
stack = malloc(sizeof(*stack));
if (stack == NULL)
return (NULL);
/* Smaller the stack, smaller the random bias */
if (thread->attr.stack_size > _thread_pagesize)
rnd = arc4random() & (_thread_pagesize - 1);
else if (thread->attr.stack_size == _thread_pagesize)
rnd = arc4random() & (_thread_pagesize / 16 - 1);
else
rnd = 0;
rnd &= ~_STACKALIGNBYTES;
/* If a stack address was provided, just fill in the details */
if (thread->attr.stack_addr != NULL) {
stack->base = base = thread->attr.stack_addr;
stack->len = thread->attr.stack_size;
#ifdef MACHINE_STACK_GROWS_UP
stack->sp = base + rnd;
#else
stack->sp = base + thread->attr.stack_size - (_STACKALIGNBYTES+1) - rnd;
#endif
/*
* This impossible guardsize marks this stack as
* application allocated so it won't be freed or
* cached by _rthread_free_stack()
*/
stack->guardsize = 1;
return (stack);
}
/* round up the requested sizes up to full pages */
size = ROUND_TO_PAGE(thread->attr.stack_size);
guardsize = ROUND_TO_PAGE(thread->attr.guard_size);
/* check for overflow */
if (size < thread->attr.stack_size ||
guardsize < thread->attr.guard_size ||
SIZE_MAX - size < guardsize) {
free(stack);
errno = EINVAL;
return (NULL);
}
size += guardsize;
/* actually allocate the real stack */
base = mmap(NULL, size, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANON | MAP_STACK, -1, 0);
if (base == MAP_FAILED) {
free(stack);
return (NULL);
}
#ifdef MACHINE_STACK_GROWS_UP
guard = base + size - guardsize;
stack->sp = base + rnd;
#else
guard = base;
stack->sp = base + size - (_STACKALIGNBYTES+1) - rnd;
#endif
/* memory protect the guard region */
if (guardsize != 0 && mprotect(guard, guardsize, PROT_NONE) == -1) {
munmap(base, size);
free(stack);
return (NULL);
}
stack->base = base;
stack->guardsize = guardsize;
stack->len = size;
return (stack);
}
void
_rthread_free_stack(struct stack *stack)
{
if (stack->len == RTHREAD_STACK_SIZE_DEF + stack->guardsize &&
stack->guardsize == _thread_pagesize) {
_spinlock(&def_stacks_lock);
SLIST_INSERT_HEAD(&def_stacks, stack, link);
_spinunlock(&def_stacks_lock);
} else {
/* unmap the storage unless it was application allocated */
if (stack->guardsize != 1)
munmap(stack->base, stack->len);
free(stack);
}
}
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