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diff --git a/lib/libc/gen/posix_spawn.c b/lib/libc/gen/posix_spawn.c
--- a/lib/libc/gen/posix_spawn.c
+++ b/lib/libc/gen/posix_spawn.c
@@ -28,6 +28,7 @@
#include "namespace.h"
#include <sys/param.h>
+#include <sys/mman.h>
#include <sys/procctl.h>
#include <sys/procdesc.h>
#include <sys/queue.h>
@@ -231,19 +232,7 @@
volatile int error;
};
-#define PSPAWN_STACK_ALIGNMENT 16
-#define PSPAWN_STACK_ALIGNBYTES (PSPAWN_STACK_ALIGNMENT - 1)
-#define PSPAWN_STACK_ALIGN(sz) \
- (((sz) + PSPAWN_STACK_ALIGNBYTES) & ~PSPAWN_STACK_ALIGNBYTES)
-
-/*
- * Below we'll assume that _RFORK_THREAD_STACK_SIZE is appropriately aligned for
- * the posix_spawn() case where we do not end up calling execvpe and won't ever
- * try to allocate space on the stack for argv[].
- */
#define _RFORK_THREAD_STACK_SIZE 4096
-_Static_assert((_RFORK_THREAD_STACK_SIZE % PSPAWN_STACK_ALIGNMENT) == 0,
- "Inappropriate stack size alignment");
static int
_posix_spawn_thr(void *data)
@@ -285,11 +274,13 @@
pid_t p;
int pfd;
bool do_pfd;
- char *stack;
- size_t stacksz;
+ char *guard, *stack;
+ size_t stacksz, pagesz;
#if defined(__i386__) || defined(__amd64__)
stacksz = _RFORK_THREAD_STACK_SIZE;
+ pagesz = getpagesize();
+
if (use_env_path) {
size_t cnt;
@@ -304,24 +295,21 @@
for (cnt = 0; argv[cnt] != NULL; ++cnt)
;
stacksz += MAX(3, cnt + 2) * sizeof(char *);
- stacksz = PSPAWN_STACK_ALIGN(stacksz);
}
- /*
- * aligned_alloc is not safe to use here, because we can't guarantee
- * that aligned_alloc and free will be provided by the same
- * implementation. We've actively hit at least one application that
- * will provide its own malloc/free but not aligned_alloc leading to
- * a free by the wrong allocator.
- */
- stack = malloc(stacksz);
- if (stack == NULL)
+ stacksz = round_page(stacksz);
+ guard = mmap(NULL, stacksz + pagesz, 0, MAP_GUARD, -1, 0);
+ if (guard == MAP_FAILED)
return (ENOMEM);
- stacksz = (((uintptr_t)stack + stacksz) & ~PSPAWN_STACK_ALIGNBYTES) -
- (uintptr_t)stack;
+ stack = mmap(guard + pagesz, stacksz, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_FIXED | MAP_ANON, -1, 0);
+ if (stack == MAP_FAILED) {
+ munmap(guard, stacksz + pagesz);
+ return (ENOMEM);
+ }
#else
- stack = NULL;
- stacksz = 0;
+ guard = stack = NULL;
+ pagesz = stacksz = 0;
#endif
psa.path = path;
psa.fa = fa;
@@ -362,7 +350,8 @@
p = rfork_thread(RFSPAWN, stack + stacksz, _posix_spawn_thr,
&psa);
}
- free(stack);
+ if (stack != NULL)
+ munmap(guard, stacksz + pagesz);
/*
* The above block should leave us in a state where we've either

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