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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 /mm/memory.c
parentmm: move the backup x_devmap() functions to asm-generic/pgtable.h (diff)
downloadlinux-dev-625110b5e9dae9074d8a7e67dd07f821a053eed7.tar.xz
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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 '')
-rw-r--r--mm/memory.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/memory.c b/mm/memory.c
index 62b5cce653f6..c3902201989f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4010,6 +4010,7 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
vmf.pud = pud_alloc(mm, p4d, address);
if (!vmf.pud)
return VM_FAULT_OOM;
+retry_pud:
if (pud_none(*vmf.pud) && __transparent_hugepage_enabled(vma)) {
ret = create_huge_pud(&vmf);
if (!(ret & VM_FAULT_FALLBACK))
@@ -4036,6 +4037,11 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
vmf.pmd = pmd_alloc(mm, vmf.pud, address);
if (!vmf.pmd)
return VM_FAULT_OOM;
+
+ /* Huge pud page fault raced with pmd_alloc? */
+ if (pud_trans_unstable(vmf.pud))
+ goto retry_pud;
+
if (pmd_none(*vmf.pmd) && __transparent_hugepage_enabled(vma)) {
ret = create_huge_pmd(&vmf);
if (!(ret & VM_FAULT_FALLBACK))