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mm/gup.c: remove some BUG_ONs from get_gate_page()

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If we end up without a PGD or PUD entry backing the gate area, don't BUG
-- just fail gracefully.

It's not entirely implausible that this could happen some day on x86.  It
doesn't right now even with an execute-only emulated vsyscall page because
the fixmap shares the PUD, but the core mm code shouldn't rely on that
particular detail to avoid OOPSing.

Link: http://lkml.kernel.org/r/a1d9f4efb75b9d464e59fd6af00104b21c58f6f7.1561610798.git.luto@kernel.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andy Lutomirski 2019-07-11 20:57:43 -07:00 committed by Linus Torvalds
parent aa712399c1
commit b5d1c39f34
1 changed files with 6 additions and 3 deletions
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9
mm/gup.c
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@ -586,11 +586,14 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
pgd = pgd_offset_k(address);
else
pgd = pgd_offset_gate(mm, address);
BUG_ON(pgd_none(*pgd));
if (pgd_none(*pgd))
return -EFAULT;
p4d = p4d_offset(pgd, address);
BUG_ON(p4d_none(*p4d));
if (p4d_none(*p4d))
return -EFAULT;
pud = pud_offset(p4d, address);
BUG_ON(pud_none(*pud));
if (pud_none(*pud))
return -EFAULT;
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return -EFAULT;