This avoids pointless races in which another CPU or task might see a
partially populated global pgd entry. These races should normally
be harmless, but, if another CPU propagates the entry via
vmalloc_fault and then populate_pgd fails (due to memory allocation
failure, for example), this prevents a use-after-free of the pgd
entry.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/mm/pageattr.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 7a1f7bbf4105..6088aa03de63 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1104,8 +1104,6 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
pud = (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_NOTRACK);
if (!pud)
return -1;
-
- set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
}
pgprot_val(pgprot) &= ~pgprot_val(cpa->mask_clr);
@@ -1113,11 +1111,16 @@ static int populate_pgd(struct cpa_data *cpa, unsigned long addr)
ret = populate_pud(cpa, addr, pgd_entry, pgprot);
if (ret < 0) {
- unmap_pgd_range(cpa->pgd, addr,
+ if (pud)
+ free_page((unsigned long)pud);
+ unmap_pud_range(pgd_entry, addr,
addr + (cpa->numpages << PAGE_SHIFT));
return ret;
}
+ if (pud)
+ set_pgd(pgd_entry, __pgd(__pa(pud) | _KERNPG_TABLE));
+
cpa->numpages = ret;
return 0;
}
--
2.7.4
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