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zero direct map pages before populating

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Zero the DM PTE/PDE pages before use. Fixes a bug on machines with more than
512GB RAM; those pages might contain previous data/junk and panic during
pmap_randomize.

Tested on various amd64 laptops, an openbsd amd64 vmm VM and an EPYC server
with 1TB RAM.

Fix supplied by Chris Cunningham, thanks!
This commit is contained in:
mlarkin
2026-04-06 18:27:33 +00:00
parent da10deba81
commit e1bb9b8c6d
1 changed files with 4 additions and 1 deletions
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5
sys/arch/amd64/amd64/pmap.c
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@@ -1,4 +1,4 @@
/* $OpenBSD: pmap.c,v 1.189 2026/03/09 13:24:13 deraadt Exp $ */
/* $OpenBSD: pmap.c,v 1.190 2026/04/06 18:27:33 mlarkin Exp $ */
/* $NetBSD: pmap.c,v 1.3 2003/05/08 18:13:13 thorpej Exp $ */
/*
@@ -798,6 +798,7 @@ pmap_bootstrap(paddr_t first_avail, paddr_t max_pa)
dmpdp = kpm->pm_pdir[PDIR_SLOT_DIRECT] & pg_frame;
dmpd = first_avail; first_avail += ndmpdp * PAGE_SIZE;
memset((void *)PMAP_DIRECT_MAP(dmpd), 0, ndmpdp * PAGE_SIZE);
for (i = NDML2_ENTRIES; i < NPDPG * ndmpdp; i++) {
paddr_t pdp;
@@ -836,6 +837,7 @@ pmap_bootstrap(paddr_t first_avail, paddr_t max_pa)
/* Next 512GB, new PML4e and L3(512GB) page */
dmpd = first_avail; first_avail += PAGE_SIZE;
pml3 = (pt_entry_t *)PMAP_DIRECT_MAP(dmpd);
memset(pml3, 0, PAGE_SIZE);
kpm->pm_pdir[PDIR_SLOT_DIRECT + curslot] = dmpd |
PG_KW | PG_V | PG_U | PG_M | pg_nx | pg_crypt;
@@ -857,6 +859,7 @@ pmap_bootstrap(paddr_t first_avail, paddr_t max_pa)
for (i = 0; i < p; i++) {
dmpd = first_avail; first_avail += PAGE_SIZE;
pml2 = (pt_entry_t *)PMAP_DIRECT_MAP(dmpd);
memset(pml2, 0, PAGE_SIZE);
pml3[i] = dmpd |
PG_RW | PG_V | PG_U | PG_M | pg_nx |
pg_crypt;