Commit b5d1c39f authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Linus Torvalds

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

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.orgSigned-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aa712399
...@@ -586,11 +586,14 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address, ...@@ -586,11 +586,14 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
pgd = pgd_offset_k(address); pgd = pgd_offset_k(address);
else else
pgd = pgd_offset_gate(mm, address); pgd = pgd_offset_gate(mm, address);
BUG_ON(pgd_none(*pgd)); if (pgd_none(*pgd))
return -EFAULT;
p4d = p4d_offset(pgd, address); p4d = p4d_offset(pgd, address);
BUG_ON(p4d_none(*p4d)); if (p4d_none(*p4d))
return -EFAULT;
pud = pud_offset(p4d, address); pud = pud_offset(p4d, address);
BUG_ON(pud_none(*pud)); if (pud_none(*pud))
return -EFAULT;
pmd = pmd_offset(pud, address); pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd)) if (!pmd_present(*pmd))
return -EFAULT; return -EFAULT;
......
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