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Fix corner case in Linux stack mappings

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We need to make sure no existing mappings exist between the
MAP_GROWSDOWN page and the guard page, since otherwise it's
not going to be able to grow down thus causing difficult to
troubleshoot failures.
This commit is contained in:
Justine Tunney 2022-10-03 13:43:52 -07:00
parent 6ba3b448f3
commit 3b4fcd8575
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GPG key ID: BE714B4575D6E328
9 changed files with 14 additions and 16 deletions
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9
libc/runtime/mmap.c
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@ -361,6 +361,10 @@ static noasan inline void *Mmap(void *addr, size_t size, int prot, int flags,
f |= MAP_STACK_openbsd;
needguard = true;
} else if (IsLinux()) {
// make sure there's no existing stuff existing between our stack
// starting page and the bottom guard page, since that would stop
// our stack page from growing down.
_npassert(!sys_munmap(p, size));
// by default MAP_GROWSDOWN will auto-allocate 10mb of pages. it's
// supposed to stop growing if an adjacent allocation exists, to
// prevent your stacks from overlapping on each other. we're not
@ -376,8 +380,9 @@ static noasan inline void *Mmap(void *addr, size_t size, int prot, int flags,
.addr == MAP_FAILED) {
return MAP_FAILED;
}
sys_mmap(p, PAGESIZE, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
_npassert(sys_mmap(p, PAGESIZE, PROT_NONE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)
.addr == p);
dm.addr = p;
return FinishMemory(p, size, prot, flags, fd, off, f, x, n, dm);
} else {