mm/memory.c: fix potential pte_unmap_unlock pte error

[ Upstream commit 90a3e375d324b2255b83e3dd29e99e2b05d82aaf ]

Since commit 42e4089c7890 ("x86/speculation/l1tf: Disallow non privileged
high MMIO PROT_NONE mappings"), when the first pfn modify is not allowed,
we would break the loop with pte unchanged.  Then the wrong pte - 1 would
be passed to pte_unmap_unlock.

Andi said:

 "While the fix is correct, I'm not sure if it actually is a real bug.
  Is there any architecture that would do something else than unlocking
  the underlying page? If it's just the underlying page then it should
  be always the same page, so no bug"

Link: https://lkml.kernel.org/r/20210109080118.20885-1-linmiaohe@huawei.com
Fixes: 42e4089c789 ("x86/speculation/l1tf: Disallow non privileged high MMIO PROT_NONE mappings")
Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/mm/memory.c b/mm/memory.c
index caefa5526b20c04397213dab8e4a6a4908ae45b9..5c2511831723e51aac9ab74c9e4fd21005cc68fa 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1984,11 +1984,11 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
                        unsigned long addr, unsigned long end,
                        unsigned long pfn, pgprot_t prot)
 {
-       pte_t *pte;
+       pte_t *pte, *mapped_pte;
        spinlock_t *ptl;
        int err = 0;
 
-       pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
+       mapped_pte = pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
        if (!pte)
                return -ENOMEM;
        arch_enter_lazy_mmu_mode();
@@ -2002,7 +2002,7 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
                pfn++;
        } while (pte++, addr += PAGE_SIZE, addr != end);
        arch_leave_lazy_mmu_mode();
-       pte_unmap_unlock(pte - 1, ptl);
+       pte_unmap_unlock(mapped_pte, ptl);
        return err;
 }