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authorJoerg Roedel <jroedel@suse.de>2020-08-07 10:40:13 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-07 09:20:57 -0700
commit995909a4e22bc7b3ea3a71388cbb62ffebd76e7b (patch)
tree2b72f1c5f8a4759b66537a1536a0515fc527290c /arch
parent9bceb80b3cc483e6763c39a4928402fa82815d3e (diff)
x86/mm/64: Do not dereference non-present PGD entries
The code for preallocate_vmalloc_pages() was written under the assumption that the p4d_offset() and pud_offset() functions will perform present checks before dereferencing the parent entries. This assumption is wrong an leads to a bug in the code which causes the physical address found in the PGD be used as a page-table page, even if the PGD is not present. So the code flow currently is: pgd = pgd_offset_k(addr); p4d = p4d_offset(pgd, addr); if (p4d_none(*p4d)) p4d = p4d_alloc(&init_mm, pgd, addr); This lacks a check for pgd_none() at least, the correct flow would be: pgd = pgd_offset_k(addr); if (pgd_none(*pgd)) p4d = p4d_alloc(&init_mm, pgd, addr); else p4d = p4d_offset(pgd, addr); But this is the same flow that the p4d_alloc() and the pud_alloc() functions use internally, so there is no need to duplicate them. Remove the p?d_none() checks from the function and just call into p4d_alloc() and pud_alloc() to correctly pre-allocate the PGD entries. Reported-and-tested-by: Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Fixes: 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area") Signed-off-by: Joerg Roedel <jroedel@suse.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/mm/init_64.c31
1 files changed, 13 insertions, 18 deletions
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 3f4e29a78f2b..449e071240e1 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1253,28 +1253,23 @@ static void __init preallocate_vmalloc_pages(void)
p4d_t *p4d;
pud_t *pud;
- p4d = p4d_offset(pgd, addr);
- if (p4d_none(*p4d)) {
- /* Can only happen with 5-level paging */
- p4d = p4d_alloc(&init_mm, pgd, addr);
- if (!p4d) {
- lvl = "p4d";
- goto failed;
- }
- }
+ lvl = "p4d";
+ p4d = p4d_alloc(&init_mm, pgd, addr);
+ if (!p4d)
+ goto failed;
+ /*
+ * With 5-level paging the P4D level is not folded. So the PGDs
+ * are now populated and there is no need to walk down to the
+ * PUD level.
+ */
if (pgtable_l5_enabled())
continue;
- pud = pud_offset(p4d, addr);
- if (pud_none(*pud)) {
- /* Ends up here only with 4-level paging */
- pud = pud_alloc(&init_mm, p4d, addr);
- if (!pud) {
- lvl = "pud";
- goto failed;
- }
- }
+ lvl = "pud";
+ pud = pud_alloc(&init_mm, p4d, addr);
+ if (!pud)
+ goto failed;
}
return;