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    Subject[PATCH 5.9 263/391] powerpc: Fix random segfault when freeing hugetlb range
    Date
    From: Christophe Leroy <christophe.leroy@csgroup.eu>

    commit 542db12a9c42d1ce70c45091765e02f74c129f43 upstream.

    The following random segfault is observed from time to time with
    map_hugetlb selftest:

    root@localhost:~# ./map_hugetlb 1 19
    524288 kB hugepages
    Mapping 1 Mbytes
    Segmentation fault

    [ 31.219972] map_hugetlb[365]: segfault (11) at 117 nip 77974f8c lr 779a6834 code 1 in ld-2.23.so[77966000+21000]
    [ 31.220192] map_hugetlb[365]: code: 9421ffc0 480318d1 93410028 90010044 9361002c 93810030 93a10034 93c10038
    [ 31.220307] map_hugetlb[365]: code: 93e1003c 93210024 8123007c 81430038 <80e90004> 814a0004 7f443a14 813a0004
    [ 31.221911] BUG: Bad rss-counter state mm:(ptrval) type:MM_FILEPAGES val:33
    [ 31.229362] BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:5

    This fault is due to hugetlb_free_pgd_range() freeing page tables
    that are also used by regular pages.

    As explain in the comment at the beginning of
    hugetlb_free_pgd_range(), the verification done in free_pgd_range()
    on floor and ceiling is not done here, which means
    hugetlb_free_pte_range() can free outside the expected range.

    As the verification cannot be done in hugetlb_free_pgd_range(), it
    must be done in hugetlb_free_pte_range().

    Fixes: b250c8c08c79 ("powerpc/8xx: Manage 512k huge pages as standard pages.")
    Cc: stable@vger.kernel.org
    Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
    Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/f0cb2a5477cd87d1eaadb128042e20aeb2bc2859.1598860677.git.christophe.leroy@csgroup.eu
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/mm/hugetlbpage.c | 18 ++++++++++++++++--
    1 file changed, 16 insertions(+), 2 deletions(-)

    --- a/arch/powerpc/mm/hugetlbpage.c
    +++ b/arch/powerpc/mm/hugetlbpage.c
    @@ -330,10 +330,24 @@ static void free_hugepd_range(struct mmu
    get_hugepd_cache_index(pdshift - shift));
    }

    -static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd, unsigned long addr)
    +static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
    + unsigned long addr, unsigned long end,
    + unsigned long floor, unsigned long ceiling)
    {
    + unsigned long start = addr;
    pgtable_t token = pmd_pgtable(*pmd);

    + start &= PMD_MASK;
    + if (start < floor)
    + return;
    + if (ceiling) {
    + ceiling &= PMD_MASK;
    + if (!ceiling)
    + return;
    + }
    + if (end - 1 > ceiling - 1)
    + return;
    +
    pmd_clear(pmd);
    pte_free_tlb(tlb, token, addr);
    mm_dec_nr_ptes(tlb->mm);
    @@ -363,7 +377,7 @@ static void hugetlb_free_pmd_range(struc
    */
    WARN_ON(!IS_ENABLED(CONFIG_PPC_8xx));

    - hugetlb_free_pte_range(tlb, pmd, addr);
    + hugetlb_free_pte_range(tlb, pmd, addr, end, floor, ceiling);

    continue;
    }

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