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authorThomas Hellstrom <thellstrom@vmware.com>2019-11-30 17:51:32 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-12-01 06:29:19 -0800
commit625110b5e9dae9074d8a7e67dd07f821a053eed7 (patch)
tree0efc9211003e1398c68ba9ca6b91ed3f43bd9af4 /include
parentbf1a12a8095615c9486f5463ca473d2d69ff6952 (diff)
mm/memory.c: fix a huge pud insertion race during faulting
A huge pud page can theoretically be faulted in racing with pmd_alloc() in __handle_mm_fault(). That will lead to pmd_alloc() returning an invalid pmd pointer. Fix this by adding a pud_trans_unstable() function similar to pmd_trans_unstable() and check whether the pud is really stable before using the pmd pointer. Race: Thread 1: Thread 2: Comment create_huge_pud() Fallback - not taken. create_huge_pud() Taken. pmd_alloc() Returns an invalid pointer. This will result in user-visible huge page data corruption. Note that this was caught during a code audit rather than a real experienced problem. It looks to me like the only implementation that currently creates huge pud pagetable entries is dev_dax_huge_fault() which doesn't appear to care much about private (COW) mappings or write-tracking which is, I believe, a prerequisite for create_huge_pud() falling back on thread 1, but not in thread 2. Link: http://lkml.kernel.org/r/20191115115808.21181-2-thomas_os@shipmail.org Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/pgtable.h25
1 files changed, 25 insertions, 0 deletions
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 3127f9028f54..798ea36a0549 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -938,6 +938,31 @@ static inline int pud_trans_huge(pud_t pud)
}
#endif
+/* See pmd_none_or_trans_huge_or_clear_bad for discussion. */
+static inline int pud_none_or_trans_huge_or_dev_or_clear_bad(pud_t *pud)
+{
+ pud_t pudval = READ_ONCE(*pud);
+
+ if (pud_none(pudval) || pud_trans_huge(pudval) || pud_devmap(pudval))
+ return 1;
+ if (unlikely(pud_bad(pudval))) {
+ pud_clear_bad(pud);
+ return 1;
+ }
+ return 0;
+}
+
+/* See pmd_trans_unstable for discussion. */
+static inline int pud_trans_unstable(pud_t *pud)
+{
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
+ defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+ return pud_none_or_trans_huge_or_dev_or_clear_bad(pud);
+#else
+ return 0;
+#endif
+}
+
#ifndef pmd_read_atomic
static inline pmd_t pmd_read_atomic(pmd_t *pmdp)
{