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Fix divide-by-zero panic when ASLR is enabled and superpages disabled

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When locating the anonymous memory region for a vm_map with ASLR
enabled, we try to keep the slid base address aligned on a superpage
boundary to minimize pagetable fragmentation and maximize the potential
usage of superpage mappings.  We can't (portably) do this if superpages
have been disabled by loader tunable and pagesizes[1] is 0, and it
would be less beneficial in that case anyway.

PR:		253511
Reported by:	johannes@jo-t.de
MFC after:	1 week
Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D28678
This commit is contained in:
Jason A. Harmening 2021-02-14 18:47:22 -08:00
parent 85d6747a69
commit 41032835dc
1 changed files with 3 additions and 2 deletions
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5
sys/kern/imgact_elf.c
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@ -1287,7 +1287,8 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
maxv1 = maxv / 2 + addr / 2;
MPASS(maxv1 >= addr); /* No overflow */
map->anon_loc = __CONCAT(rnd_, __elfN(base))(map, addr, maxv1,
MAXPAGESIZES > 1 ? pagesizes[1] : pagesizes[0]);
(MAXPAGESIZES > 1 && pagesizes[1] != 0) ?
pagesizes[1] : pagesizes[0]);
} else {
map->anon_loc = addr;
}
@ -1297,7 +1298,7 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
if (interp != NULL) {
VOP_UNLOCK(imgp->vp);
if ((map->flags & MAP_ASLR) != 0) {
/* Assume that interpeter fits into 1/4 of AS */
/* Assume that interpreter fits into 1/4 of AS */
maxv1 = maxv / 2 + addr / 2;
MPASS(maxv1 >= addr); /* No overflow */
addr = __CONCAT(rnd_, __elfN(base))(map, addr,